An introduction to technological applications of Molecular Gastronomy. Part 2

III.8.4. Test with the recipe

III.8.4.1. Material:

• 400 mL of white stock, reduced in half.

• 2 soft-boiled eggs.

• 100 mL of single cream.

• 1 spoon of vinegar.

• 1 red sweet pepper.

• Salt and pepper.

III.8.4.2. Method:The method is identical as the one explained in III.8.2.

III.8.4.3. Results:This test with the use of white stock doesn't give a significant result. There is a simple release of smoke, which looks more like steam than a real mist. The ice cube takes several minutes to melt.

III.8.4.4. Discussion/Interpretation:The air around the glass is cold and the smoke is hot (close to 100 °C). To spread the smoke along the glass, the gas has to be denser than the air.

The difference of ingredients doesn't seem to have any influence on the result.

The intended effects of smoke look like smokes done with liquid nitrogen or dry ice. We suggest realizing similar tests by using some liquid nitrogen and some dry ice to compare visually the obtained results.

III.8.5. Note on the dry ice and the liquid nitrogen:

III.8.5.1. Effects of smoke:Dry ice is one of the most extraordinary known sources of cold. Each kilogram frees 150 frigories (655 kJ). It frees cold three times more than the same volume of water ice, and at a much lower temperature.

The temperature of dry ice is –80 °C and it becomes carbon dioxide. The dry ice is usually and widely used for transport, in laboratories and in food industries. The dry ice is often recommended for the respect for the cold chain.

III.8.5.2. Precautions of use:

• Use gloves and glasses during its manipulation. Do not swallow; risks of burning.

• Do not carry more than 20 kg of dry ice in a car, risk of asphyxiation with the carbon dioxide.

• Do not put some dry ice in a hermetic bowl, risk of explosion.

• Do not store the dry ice in a confined room.

• Keep out of reach of children.

The same properties are obtained with some liquid nitrogen, another substance which produces some "smoke". The liquid nitrogen (–176 °C) is even more dangerous to manipulate (the company Air Liquide disadvises to use it in a gourmet restaurant by concerns of security). The contact with this product can cause burns and can, in high dose, provoke risks of asphyxiation. The same rules of security have to be applied.

III.8.5.3. Two theories on the smoke formation:

• In practice, dry ice loses some carbon dioxide when it warms up. The carbon dioxide is a gas denser than the air; it goes down, compared to the steam and is more visible.

• The very cold gas can cool the ambient air. The water vapour in air can condense and make a natural smoke (similar to a cloud), denser than the air.

III.8.6. Test with some dry ice and liquid nitrogen:

III.8.6.1. Material:

• 400 ml of reduced "fond blanc" in half.

• 2 soft-boiled eggs.

• 100 ml of liquid cream.

• 1 spoon of vinegar.

• 1 red sweet pepper.

• Salt and pepper.

III.8.6.2. Method:The method is identical to the former recipe. The ice cube is however an ice cube of dry ice. In the test with the liquid nitrogen, we pour liquid nitrogen after having poured our warm liquid in the glass, to limit the projections of liquid nitrogen.

III.8.6.3. Results:The tests are decisive with some dry ice (an ice cube of 1 mm³ in 50 ml of water gives a satisfactory smoke for the contents of a glass, as a champagne flute).

With some liquid nitrogen, it gives the same effect as on the picture, with a smoke of the same density. It lasts during the complete fusion of the ice cube (5 min approximately).

III.8.7. Conclusion:The tests in the dry ice and in the liquid nitrogen give the visual characteristics of the clear smoke; these results are identical to those of the picture.

Ice cubes can be cooled at the temperature of the liquid nitrogen and the dry ice. However, the tests realized this way give only a smoke during the first 5 seconds, before behaving as a simple ice cube in a glass.

This "thermal shock" finally does not exist, it is not reproducible without the use of supplementary material such as the dry ice or the liquid nitrogen.

It is necessary to make sure that all the dry ice or all the liquid nitrogen has completely disappeared from the glass to be able to eat it: it is thus necessary to measure the temperature variation of the glass according to the time and the volume of the employed product, as well as the time of evaporation of the product.

III.8.8. Other suggestions openings, ideas, applications of the technology:With the use of dry ice, the temperature of the liquid inside of the glass does not vary or just a bit (1 to 2 degrees measured with a thermocouple). This means that the liquid can be poured at the consumption temperature.

The frozen glass allows to keep a film of ice all around the glass, which adds an aesthetic touch to the phenomenon of released smoke.

Also, the use of an opaque liquid allows to hide the origin of the smoke.

A flavour may be able to let out. However, colouring the smoke seems to be difficult because the colour effect is linked to the density of the gas. It would be necessary to try to colour the liquid nitrogen or the dry ice.

There is an idea to use soup plates with a double bottom to introduce the product, without risking a contact with the food.

III.9. Effervescence with citric acid and sodium hydrogen carbonate

III.9.1. Objective:We wish to obtain an effervescence in a dish, using sodium hydrogen carbonate NaHCO₃ and some acid, like lemon juice or vinegar.

III.9.2. Introduction:Sodium hydrogen carbonate NaHCO₃, in presence of citric acid, induces an effervescence according to this scheme of reaction:

Citric acid + 3 sodium bicarbonate → base from the acid + 3 H₂O + 3 CO₂

This reaction occurs by the contact of the two reagents, mostly in aqueous solution.

As it is shown above, this reaction releases some carbon dioxide, involving effervescence.

III.9.3. First test:

III.9.3.1. Material:

• Sodium bicarbonate (powder at 1 % of humidity), supplied by Louis François Inc.

• Juice of a freshly squeezed lemon.

• Citric acid (at 1 % of humidity), supplied by Thiercelin Inc.

• Tap water.

• Bowls.

• Caster sugar.

III.9.3.2. Method:

1. Prepare 3 different solutions of sodium bicarbonate:a. Some powder,b. A solution of tap water with 1% of sodium bicarbonate,c. A gel made of the former solution with 1% of gelatine.

2. Prepare 3 different solutions of lemon juice:a. The natural juiceb. A gel made of lemon juice and 1% of gelatinec. A gel made of lemon juice and 0.5% of gelatine.

3. Put a teaspoon of one solution of sodium bicarbonate in contact with a teaspoon of one solution of lemon juice in a plate. Then taste the mixture.

III.9.3.3. Results:In the mouth, the reaction of effervescence works after several seconds, but its intensity is not very important.

It has to be noted that the mixture gives an unpleasant sensation before beginning of the reaction between the two reagents (effervescence).

The results are given in the appendix 9.

III.9.3.4. Discussion/Interpretation:Sodium hydrogen carbonate gives an unpleasant taste. It has to be employed with a minimum quantity, whereas the acid would be used in excess.

The effervescence is not hard enough and it takes time to start the effervescence. A solution could be to play with the concentrations of the initial products.

III.9.4. Tests with various concentrations of hydrogen carbonate. Estimation of the effervescence intensity.

III.9.4.1. Materials and method:These new tests were realized with solutions at 5 %, 4 % and 3 % of hydrogen carbonate.

III.9.4.2. Results:The results are given in Appendix 10.The effervescence is higher with a mixture of powder than with solutions or gels.

III.9.4.3. Discussion/Interpretation:Mixtures of two solutions give a similar sensation as a fizzy drink kept in mouth. They don't produce an intense effervescence.

Concerning the use of gels, it is necessary to chew them and the gels give a foamy sensation more than a real effervescence. Indeed, the molecules are less available in a gel than in a solution. Nevertheless, the gel is more pleasant than solutions because it lowers the acidity of the lemon juice and it allows keeping the mixture in mouth much longer than a liquid that is directly swallowed.

During these tests, the solution of hydrogen carbonate made with tap water gave an unpleasant taste. However, for a real dish, the taste of hydrogen carbonate would be hidden by a tasty solution used instead of tap water, even if the bicarbonate could change a bit the initial taste of the solution.

The length of the fizzy sensation and of its initiation is identical if solutions or gels are used. In both cases, the reaction takes too much time to start (3 to 5 s on). A gel prevents the papillae from being in touch with the bubbles and a solution is too quickly swallowed. A significant effervescence could be obtained with a direct absorption of a mixture of powders, the saliva would mix the two reagents.

III.9.5. Use of powders:

III.9.5.1. Material:

• Sodium hydrogen carbonate (powder at 1 % of humidity), supplied by Louis François.

• Citric acid (1 % of humidity), supplied by Thiercelin.

• Caster sugar.

• Bowls.

• Oven, brand MODULAR SALVA. Temperature = 40 °C (Precision of 3 °C).

• Ten raspberries.

III.9.5.2. Method:

1. Weigh separately in a bowl 5 g of sodium hydrogen carbonate, 5 g of citric acid, 10 g of caster sugar.

2. Put these three bowls in the oven for 48 hours.

3. Check if the powders are very dry.

4. Mix the powders.

5. Put some mixture inside a raspberry.

III.9.5.3. Results:The mixture of powder gives a very good effervescence, with a sensation of sparkling wine in mouth. Also, the sugar eases the unpleasant taste of powders.

III.9.5.4. Discussion/Interpretation:The mixture of powders gives a significant and lasting effect in mouth; compared to the other tests with solutions of gels. The use of a raspberry gives a satisfactory result, as this fruit isn't wet and doesn't react with the powder by itself. However, a mixture of powders directly put on the tongue gives an unpleasant sensation as the reaction is too violent.

The drying step is important as the powder can react with the air humidity and be less efficient in mouth. Also, the powders have to be dried separately as the sugar can crystallize.

The best result is given by these percentages (in weight): 25 % of sodium hydrogen carbonate, 25 % of citric acid, 50 % of caster sugar.

Which quantity of powder can we ingest (food security, ADI)?

III.9.6. Conclusion:The effect of effervescence is interesting, it gives some sharpness due to the bubbles and some lightness due to the foam created in mouth. The mix of powders seems to be the better way of making a nice and effective effervescence. However, the direct contact of powder in mouth is unpleasant, it is then necessary to put the mixture inside a dry support.

III.9.7. Other suggestions openings, ideas, applications of the technology:It could be interesting to use a gel or a liquid with a thickening agent to wet and moisten in mouth the mixture of powders, instead of putting powders in solutions or gels.

We can add different powders to the mixture; the only condition would be to keep a dry environment. In the case of the sugar, its hygroscopic properties allow to trap the excess of humidity and prevent from a possible reaction with the air. Another idea is to put the mixture of powders in oil, to avoid any contact with the air.

We can reproduce this type of effervescence in a jelly (see III.4). The main problem with the use of a gel is the too long contact between the molecules of the powders. A solution could be to whisk the gel before, in order to break them up. Also, we could make some gels which are less hard.

With this technique, we can realize decorations, foamy or soft.

III.10. Improvement of the texture of a cream of black rice

III.10.1. Objective:Pierre Gagnaire wished to transform his cream of black rice in order to obtain an innovative light texture. The tests were made with an emulsion and a foam.

III.10.2. Introduction:Certain special kinds of rice are appreciated not only for their flavour but also for their colour, which is determined by their pigment (anthocyanins) contained in the various skins of the seed. Due to these molecules, the colour of rice endosperm can change from white and various translucent nuances to red, purple and black.

In China, the unmanufactured black rice is used as natural colouring agent in pastries, dumplings, porridge, new year's cakes and black wine. It is also considered as very important for nutrition, rich in vitamins B, in calcium and in some oligoelements (in particular manganese).

The Jieguno variety, purple-black coloured, is supposed to strengthen the immune system and to help bone formation. China is now marketing more than 54 modern varieties with a high yield of production, high resistances to pests and a good flavour quality. However, the black rice represents less than 1.3 % of the rice culture of the country.

The researchers consider that the red rice, of which the biggest part is transformed into white rice (usual consumption), possesses a bigger tolerance in the unfavourable environment, such as infertile soils and mountainous zones.

III.10.3. Recipe of the restaurant:

1. Slice thinly onions and fry them in oil.

2. Add some rice and brown it lightly.

3. Pour some white stock, which is the cooking juice.

4. Put the pan in the oven, and let it cook for a long time.

5. Once the rice is cooked and the juice is reduced, mix the mixture in a Blender, to obtain a smooth, homogeneous and creamy texture.

6. Add some fond blanc to obtain the right texture.

III.10.4. A foam of cream of black rice:

III.10.4.1. Objective:Very light foams called "cristaux de vent" were introduced more than 15 years ago by Hervé This (public lecture at the Clarendon Laboratory, Oxford). We tried to make some of these "cristaux de vent" with whipped egg white and some cream of black rice.

III.10.4.2. Material:

• 90 g of egg white (3 egg whites), supplied by Louis François.

• A big pinch of salt (4 to 5 g).

• 100 g of cream of black rice.

• Electric robot brand Kitchen Aid for a container of 25 cm of diameter (10 speeds).

III.10.4.3. Method:

1. Slightly warm (about at 40 °C) the cream of black rice and whisk.

2. Whip the egg white.

3. Add the cream of black rice drop by drop, when the whites start to turn into foam.

4. Stop whisking when the right consistency is obtained.

III.10.4.4. Results:The manufacture of foams was a success. The making of these "cristaux de vent" was technically easy. The results of "cristaux de vent" made with some cream of black rice is given in appendix 11.

III.10.4.5. Discussion/Interpretation:The foam could even be lighter. The added cream seems to make the foam heavy. Also if there are more egg whites, the taste of the cream of black rice is not intense.

The presence of fat in the cream of black rice and the presence of some rice skins can prevent from a good foam setting.

III.10.5. Emulsion with some groundnut oil:

III.10.5.1. Objective:We want to make an emulsion with the cream of black rice and some oil, like a mayonnaise. It would be hand whisk to get big air bubbles in the mixture, in order to highlight the taste of the cream of black rice.

III.10.5.2. Material:

• 30 g of black rice.

• 30 g of white stock.

• One pinch of salt.

• Some groundnut oil.

• Red wine of Haut Médoc wine.

• A stainless steel bowl.

• A hand whisk (stick of 0.7 mm of diameter).

III.10.5.3. Method:

1. 24 hours before the experiment, mix some oil and some wine (same amount). Separate the two phases and keep the used one.

2. Mix the cream of black rice with the white stock.

3. Warm the mixture then let it cool at room temperature.

4. Add one pinch of salt and homogenize.

5. Whisk the mixture while adding some tasty oil, like a mayonnaise.

III.10.5.4. Results:We observed a loss of the colour of the cream of rice which clarifies as we incorporate some oil, tasteful loss of the cream of rice for the benefit of that fragrant oil. The mixture wins in unctuousness, which is similar to that of the mayonnaise. We lose however the sweetness of this cream of black rice. At the level of the taste, this device is not convenient for the Chef because the taste of the cream of black rice is not any more the same.

III.10.5.5. Discussion/Interpretation:The emulsion did not correspond to the expectations of the Chef, but the change of colour is an interesting point to exploit. We may try to do this emulsion with the aim not to lighten the black rice cream.

III.10.6. Conclusion:

III.10.6.1. Evaluation:The experiments give positive results on a technical point of view, but do not answer to the expectations of the Chef on the improvement of the cream of black rice. After these two experiments, the cream of black rice by itself seems to be the best texture for the Chef.

III.10.6.2. Conclusions:It seems that improving a cream of black rice (foam or emulsion) is difficult as this recipe is already complex.

III.10.7. Other suggestions openings, ideas, applications of the technology:The colour given by the black rice can be introduced into a recipe of bread, like cuttlefish ink, for example.

III.11. Duo of warm and cold gels

III.11.1. Objective:The aim of this test is to give a new sensation of "hot and cold" at the same time, by the use of two jellies (or very thick liquids) set side by side in a glass.

III.11.2. Introduction:For the hot gel, it is necessary not to be thermoreversible or to have a high melting point. For the cold gel, it has to bear a high temperature, at least for 5 minutes (time of setting, serving and eating the dish). Alginates, which aren't thermoreversible seem to be appropriate. The gels (hot and cold) were made of milk and 1 % of alginates.

III.11.3. Test with two gels made with milk and alginates:

III.11.3.1. Materials:

• 100 g of half skimmed milk (pasteurised).

• Some caster sugar.

• Sodium alginate (E401 additive E 40), supplied by Louis François.

• Food colouring agents.

• Hand whisk.

• A glass (4 in 5 cm of diameter).

III.11.3.2. Method:

1. Mix 1 g of caster sugar with 1 g of sodium alginate.

2. Simmer the milk.

3. Add the mixture and whisk.

4. The solution thickens rapidly. Whisk for 1 min to remove lumps and smooth the texture of the mixture.

5. Separate the mixture in two parts and colour each part with a different colouring agent.

6. Put the two mixtures in the fridge and let them set.

7. The one will then be left with the refrigerator in 2 °C to lower its temperature to that of the refrigerator.

8. Once set, one will be cooled at 2 °C and the other one will be warmed at 50 °C in a microwave.

9. In a glass, put a piece of greaseproof paper to separate the gels.

10. Pour the cold gel into one of the compartments, then the warm gel in the other one.

11. Remove delicately the greaseproof paper. Eat the two gels together to get the difference of temperature.

III.11.3.3. Results:The gels set without any problem. By the way, it is better to dilute the alginate powder with some water before pouring it into the milk because it sets in gel immediately, due to the presence of calcium ions in the milk.

III.11.3.4. Discussion/Interpretation:Other gelling agents were used to make the cold gel. In contact with the hot gel of alginate, either they had a fast and important syneresis, or they melt instantly. An idea was to use a thickening agent: for example, the gelatine melts between 20 and 30 °C.

A gel of alginate gives very satisfactory results, but it has to be noted that the use of some sodium alginate requires the presence of calcium to set in gel.

III.11.4. Thermal equilibrium.

III.11.4.1. Materials and method:With the same gels as in III.11.3.2., measure the temperature with a thermocouple (MAFTER k beach 50 – 950 °C; uncertainty 1 °C).

III.11.4.2. Results:The gels cool quite slowly and the difference of temperature between a hot and a cold gel in contact is still perceivable after 20 min (there is still a difference of 20 °C).

The temperature was taken near the edge of the glass. But right in the middle of the gel, the temperatures were obviously bigger. It seems that the thermal exchange between the middle of the gel and its borders is bigger than the thermal exchange between the two gels at different temperatures.

III.11.5. Conclusion:This experiment is easy to do, it does not require a particular technique. The gels of alginates are restricted to the use of solutions containing some calcium ions, as dairy products. However, the other gelling agents can be employed to obtain similar effects.

Also, Pierre Gagnaire wished very smooth gels, which behave more like a thick liquid than a solid gel. Here, we could have used a thickening instead of a strong gel. For example, the use of starch can lead to good results, without any new ingredients or techniques. This technology is thus easy to set up in the restaurant.

III.11.6. Other suggestions openings, ideas, applications of the technology:The behaviour of these gels and the other thick sauces could be used to set them on a hot plate, or with hot ingredients.

III.12. Sizing of meat by the transglutaminase enzyme

III.12.1 Objective:Using transglutaminase enzyme can change the consistency of gels. It should be firmer and thus it should give a crunchy sensation in mouth.

The aim of this test is to be able to stick some fragments of meat together, for example in the case of terrines.

III.12.2. Introduction:

III.12.2.1. Properties of the transglutaminase enzyme:Transglutaminase is an intracellular ubiquitous enzyme, which catalyzes covalent links between proteins. This enzyme is a specific catalyst for proteins that are glutamic group donors.

This enzyme catalyses the formation of covalent links between an amino group of a protein and an amino group of a peptide from the glutamine. For example, this enzyme contributes to the coagulation and these links are irreversible.

III.12.2.2. Use in food industries:Transglutaminase enzymes are now produced by industries and they are used in numerous industrial processes, in particular the food alterations of meat-based products (ham for example) and fish-based products (surimi for example). The properties of these texture agents and binder agents allow to use them instead of other gelling agents or polyphosphates.

III.12.2.3. Example of a commercial product:The transglutaminase enzyme is sold as a powder. It can be used either directly as a powder, or in solution. Ajinomoto Inc, represented in Europe by Unipex Inc, is a supplier and a user of a type of this enzyme: Activated (produced by fermentation of Streptoverticillium mobaraense).

It takes place in the processes of food alterations of meat-based products according to the following reactions:

• Acyl transfer

• Polymerisation reaction

• Reaction of amide hydrolysis

Transglutaminase enzymes in food industries have several possible applications: to strengthen the emulsions, the phenomena of gelification, to increase the viscosity, the thermal stability, the linking and water retention properties, etc.

III.12.3. Technology transfers:In practice, these enzymes stick proteins together. In the restaurant, it could be used as a different gelling agent or for strengthening the firmness of a gel, thickening a sauce, or sticking meat or fish tissues together.

Its introduction in kitchen and its manipulation were not realized, but the idea will be exploited further.

III.13. Insulating properties of foams

III.13.1. Objective:The aim of these tests was to give hardness to foam that is soft and to use the insulating and waterproof properties of foams to trap a liquid inside.

III.13.2. Introduction:Foam is an insulating system which allows creating a waterproof coat containing a liquid. We covered the foam with a solid phase (a dough) to bring hardness to the softness of the foam.

Ice-cold balls of broth (or other tasty liquid) were covered by foam (made with egg whites) and all was covered by dough (bread). This preparation was cooked in the oven (until the cooking of the dough). After cooking, proteins of the egg whites hardened and the foam became solid, trapping the liquid inside.

III.13.3. Try with three layers: liquid, foam and solid.

III.13.3.1. Material and method:

• A tasty liquid (here, a white stock).

• Some mousse (here, a mousse of veal).

• Dough (here, dough of standard bread).

• A ventilated oven, brand LAINOX; from 50 to 350 °C (Precision 5 °C).

• A Pacojet.

• Stamps in stainless steel (125 mm of diameter).

• A sherbet spoon.

• Make a sherbet with the fond blanc put in the Pacojet.

• Make balls of ice with the sherbet spoon.

• Realize discs of dough (1 to 2 mm of thickness) with the stamps.

• On each disc of dough, put a spoon of mousse.

• Add a ball of sherbet on the top.

• Cover completely the ball of sherbet with the mousse.

• Close the dough as a pouch.

• Cook in the ventilated oven at 180 °C until the dough is cooked (15 min ± 1 min).

III.13.3.2. Results:On six tries, only one gave an intact product, with the mousse trapping the liquid inside. The mousse was as hard as expected, giving a nice firmness in mouth. The liquid was released by chewing the mousse.

However, the dough was too fine and too dry, and it wasn't crunchy. Also, it didn't set with the mousse, which made its cutting difficult.

III.13.3.3. Discussion/Interpretation:While cooking, the liquid passed through the broken dough because the mousse didn't trap the liquid correctly. Indeed, during their manufacture, the balls of ice melted quickly and made the setting of the mousse difficult. Furthermore, the weight and the hardness of the ice balls with regard to the mousse could have caused a hole in the mousse layer.

According to the Chefs, the use of batter instead of bread dough would give a touch of crispiness. The idea was to cook first the mousse trapping the liquid inside and then to add and cook the batter. Nevertheless, the solid coat in contact with the foam had the interest to avoid the formation of air bubbles between the different layers. Thus, different experiments were realized in terms of cooking.

III.13.4. Cooking first the foam and then the solid coat.

III.13.4.1. Material and method:

• Some foam (here, a foam of veal).

• Some juice (here, we tried with some tap water).

• Sherbet spoon.

• Honeycombed (half spheres from 20 to 25 mm of diameter and 15 mm of depth) mould (in polycarbon), brand Elixix.

• Vapour oven, brand Convotherm OEB, precision 2 °C.

• Freeze the juice, put the ice in the Pacojet.

• Make some spheres of ice (10 mm of diameter) with the sherbet spoon, and store them in the deep freeze.

• Put ½ teaspoon of mousse in each alveolus of the honeycombed mould. Spread it until it reaches the edges of the mould (its thickness would be about 5 mm).

• Put a half of a frozen sphere on the top and cover it with some mousse.

• Cook in the oven between 60 and 80 °C (here the tests were realized at 80 °C during 10 min).

III.13.4.2. Results:This technique gave very satisfactory results. Indeed, the external coats of mousse remained closed for 5 tests on 6. The shape is homogenous and also, the turning out is easy.

The liquid is well trapped inside and the foam, which remains soft, is harder. Foam here performed its role of insulation.

III.13.4.3. Discussion/Interpretation:The second part of foam had to be added quickly as the ice balls can melt very fast, making a film of water, which can prevent from a good setting of the mousse.

III.13.5. Conclusion:Balls of foam with a liquid heart are easy to obtain, the concept is interesting. The cooking of foam is a technique known by the team, only the manufacture can add some novelty. These balls of foam can be realized with any foam containing egg whites and any liquid that can freeze.

III.14. Cooking fish bones

III.14.1. Objective:We wanted to extract particular flavour from the scales of red mullet by extracting hydrophobic and hydrophilic molecules with oil and water respectively. This method was inspired from the technology n°3.

III.14.2. Material:

• 40 g of fish bones (red mullet).

• 10 g of clarified butter.

• ½ l of water, salt, pepper.

• A copper pan with its lid.

• White wine vinegar.

III.14.3. Method:

1. Make a marinade with the fish bones, some white wine vinegar (neutral) during 48 hours.

2. Drain the fish bones and remove the skin.

3. Cook them quickly in the clarified butter and add some.

4. Add water and heat until it boils.

5. Cook for 1 hour then keep hot during 3 hours.

6. Cook again for one hour.

III.14.4. Results:The taste is very acidic due to the vinegar, it tastes like a fish soup. We do not perceive any original taste or particular savour.

III.14.5. Discussion/Interpretation:There are some difficulties for separating the flesh from the fish bones and for removing a significant quantity of fish bones. This takes a long time (1h15 for 40 g of fish bones).

The taste of fish soup can be due to the presence of some flesh on fish bones. The flesh is indeed decomposed by the vinegar, but a certain quantity stays on fish bones.

This experiment does not reveal the particular savours given by some sapid molecule expected to be present on the fish bones. However, this can be due to an excess of fish flesh or a lack of fish bones.

III.14.6. Conclusion:This experiment did not give significant results, we can't know if some sapid molecules are present in fish bones and if they can play a role in kitchen. Nevertheless, the experiment has to be done again with more precision.

III.15. Meat or fish millefeuilles

III.15.1. Objective:H. This proposed to P. Gagnaire to realize a "millefeuilles" with raw meat in order to make like an artificial ham (with many layers of fat and meat). The use of a tasty fat would give taste to the meat, and a special consistency, thus fulfilling a new programme on organization of the food space.

III.15.2. Introduction:We realized a "millefeuilles" from meat with thin sheets of meat intertwined with some tasty fat. The way of slicing it can be done in various directions.

III.15.3. First attempt with the Iberian palette.

III.15.3.1. Material:

• A piece of Iberian ham (circa 150 g).

• A sheet of greaseproof paper (40 cm x 60 cm).

• A rolling pin.

• 30 g of flavourful clarified butter.

• An electric chopper (graduation of 0.5 mm; Precision 0.1 mm).

III.15.3.2. Method:

1. Cut very thin slices of meat (here thickness between 0.4 and 0.5 mm).

2. On a sheet of greaseproof paper, put the thin slices of meat.

3. Brush the sheet of greaseproof paper with some clarified butter.

4. Fold the meat in three in the length.

5. Repeat the steps 3 and 4 as much as possible to obtain as many sheets as possible. To fix the different layers together, it is possible to roll them.

6. Slice the "millefeuilles" and serve.

III.15.3.3. Results:The consistency of the slices looks like the texture of a sausage. From a taste point of view, the taste of the butter is not present enough to reduce the taste of the meat. We wish to give some taste to this butter.

III.15.3.4. Discussion/Interpretation:The texture given by the use of raw meat is too close to the texture of a sausage. It is necessary to use another kind of meat or to add another solid layer.

III.15.4. Trial with a raw fillet of beef, in carpaccio.

III.15.4.1. Material:

• 250 g of beef meat.

• A deep freeze.

• An electric chopper (graduation of 0.5 mm; Precision 0.1 mm).

• A sheet of greaseproof paper (40 cm x 60 cm).

• A rolling pin.

• 30 g of tasty melted butter.

• Confectioner's paintbrush.

III.15.4.2. Method:

1. Put the meat in the deep freeze.

2. Once frozen, cut thin slices of meat (about 0.5 mm).

3. On a sheet of greaseproof paper, put the slices side by side.

4. Brush the sheet of greaseproof paper with some butter.

5. Fold the meat in three in the length.

6. Repeat the steps 4 and 5 as often as possible to increase the "feuilletage".

7. Slice the "millefeuilles" and serve.

III.15.4.3. Results:We realized a "millefeuilles" by folding the meat 4 times, which gave 3⁴ = 243 sheets of butter and meat. The different slices adhere suitably between them. However, we can't see the "feuilletage" clearly, the different sheets don't appear distinctly.

III.15.4.4. Discussion/Interpretation:It was hard to slice this "millefeuilles". Also, it's impossible to re-freeze it because of the risk to develop cryophilic bacteria.

The taste of the different ingredients doesn't become impaired but in terms of texture, the result doesn't give a particular sensation in mouth.

Indeed, the different layers of the "millefeuilles" are not clearly distinguished, it looks more like some minced meat. It may be necessary to cut thicker slices of meat without freezing it, then freeze the "millefeuille" and cut thin slices of it.

Here, the butter was without any particular taste, in order to check if the meat taste wasn't impaired. In a second time, we can use a tasty butter, to add some other taste to the recipe.

If we want to mix different meats, we have to take into account their different texture and tenderness in the realization of the "millefeuilles".

III.15.5. Trial with raw salmon, and some butter cooked with orange, lemon, parsley, basil and coriander.

III.15.5.1. Material:

• 250 g of salmon flesh (from the tail).

• A tasty butter (with orange, lemon, parsley, basil and coriander).

• A deep freeze.

• An electric chopper (graduation of 0.5 mm; precision 0.1 mm).

• A sheet of greaseproof paper (40 cm x 60 cm).

• A rolling pin.

III.15.5.2. Method:

1. Cut thin slices of fish (approximately 2 mm).

2. On a sheet of greaseproof paper, put the slices side by side.

3. Brush all the surface of greaseproof paper with some butter.

4. Fold the fish in three in the length (to fix the different layers together, it is possible to roll them).

5. Repeat the steps 3 and 4 as often as possible to realize the maximum number of sheets.

6. Put the "millefeuilles" in the deep freeze, and cut some thin slices once frozen.

III.15.5.3. Results:The "feuilletage" is well realized and the taste of raw salmon and butter is present. The different layers are visible and they can even be felt in mouth.

III.15.5.4. Discussion/Interpretation:Slices are much thinner than with the previous experiments. The texture is interesting because the different sheets of the "millefeuilles" behave differently in the mouth than a classic piece of meat. Furthermore, the chewing allows the release of fat, which adds another taste to the "feuilletage". The Chef likes this new texture and the fact that a very tasty butter was added.

Also, as it is frozen, the "millefeuilles" can be prepared in advance, which saves time. This technique is easy to introduce in the kitchen, it doesn't add any particular problems.

III.15.6. Formalization according to the formalism of the dispersed systems:Puff pastry is obtained by inclusion of butter (B) in an envelope made by dough (D). The envelope (DσBσD) is stretched and folded up in three on itself, and this is repeated 6 times. This gives this system:

(DσBσD)σ(DσBσD)σ(DσBσD)

Two sheets of dough (D) side by side can be considered as only one sheet (D)σ(D) = D. Thus(DσBσD)σ(DσBσD)σ(DσBσD) = Dσ(BσD)σ3 then Dσ(BσD)σ9, Dσ(BσD)σ27, Dσ(BσD)σ81, Dσ(BσD)σ243, Dσ(BσD)σ729.

As meat can be considered as a dispersion of a liquid (water W) in a solid continuous phase (the network of collagenic tissue S), the formula here would be obtained by using (W/S) instead of D.

For butter, the exact structure is not known, because the localization of water has not been studied, but it could be posited that the formula is B = ((W/O)/S).

Proportions of the various ingredients could be considered, but it is probably not useful here. Hence the final formula for puff pastry is:

(W₁/S₁)σ(((W₂/O)/S₂)σ(W₁/S₁))σ243.

Of course, the number of foldings can change easily.

III.15.7. Conclusion:The texture is interesting and this technique is easy to prepare. It gives a new way of eating meat and fish.

III.15.8. Other suggestions openings, ideas, applications of the technology:

• Play with the thicknesses of the different layers.

• Alternate the types of meat in the various layers.

• Mix meat and fish?

III.16. Jellified foams

III.16.1. Objective:We would like to make foam with a solution of gelatine to give a light and foamy texture to a gel, when the mixture is cool.

III.16.2. Introduction:We know that foam is a dispersion of a gas in a liquid. In a solution containing surfactants (i.e. proteins that lower the surface tension at the interface of two different phases), it takes less energy to make a foam.

When a solution (i.e. water) is whipped, some air comes into it. The longer the whipping, the more numerous and the smaller the bubbles of air. This phenomenon can be explained by the formula:

G + W → G/W

If we consider a solution with surfactants (i.e. gelatine), this solution is indeed a dispersion of liquid into a continuous solid phase (proteins), which can be written as:

W + S → W/S

We wanted here to make a foam with this solution of gelatine. When this solution is whisked, some air comes into it and some bubbles are formed. Once cooled, the gelatine sets and the air is trapped into the gel. We obtain a jellified foam. Its formula is:

1. G + W → G/W

2. G/W → (G/L)/S

What could be the maximum volume of air that can be inserted into this solution of gelatine?

III.16.3. A jellified foam from a stock:

III.16.3.1. Material:

• 500 g of white stock.

• 50 g of gelatine.

• Electric whisk (10 speeds).

• Hand whisk with sticks of 0.7 mm of diameter.

III.16.3.2. Method:

1. Melt the gelatine in the hot white stock and homogenize.

2. Put the mixture in a bowl and use the electric whisk (speed 10). Cool the mixture by putting the bowl in frozen water, the gelatine would get hard.

3. Stop the whisk, when the mixture gives a firm foam and when the gelatine sets in gel. Store it in the fridge or use it directly.

This experiment was done with different concentrations of gelatine. The results and the observations for each gelatine concentration is in Appendix 13.

III.16.3.3. Results:The foam, clearer than the solution, increases in volume. Then, the gelatine starts to set in gel: the foam darkens, the volume of air bubbles decreases and their number increases. When all the liquid is transformed into foam, the preparation is almost ready, but it is necessary to avoid the making of lumps. Put in the fridge (+2 °C), the foam hardens into a gel. In the fridge, the foams finishes to set, and the texture is different than a gelled foam not cooled.

The tests reveal that a concentration in gelatine higher than 6% doesn't give a good result. Indeed, the solution of gelatine sets in the bowl because the mixture is too viscous to be whisked. When the concentration of gelatine is lower, the volume of solution not used to make foam is smaller and also, the size of the bubbles are bigger.

In gels and foams, the taste is sweeter, less strong than the one you can find when you eat the tasty food. The idea is to use a gelled foam in order to moderate a taste that is usually strong. For example, the acidity of a lemon juice or the spicy part of a hot pepper were tested in a gelled foam.

III.16.4. Slightly acid and sweet foam, like a meringue.In a meringue, the sugar (that is hygroscopic) allows to firm up the mixture, and also to decrease the intensity of the acidity. It is what we want to introduce in foam with gelatine.

III.16.4.1. Material:

• 200 g of squeezed lemon juice.

• 5 g of gelatine Rousselot (leaves).

• 5 g of honey.

• 100 g of sugar.

• Electric whisk (10 speeds).

III.16.4.2. Method:The method is the same as previously, where the sugar and the honey are dissolved in the lemon juice.

III.16.4.3. Results:The result is very satisfactory regarding the lightness, the smoothness and the great taste of lemon. Also, the use of sugar sweetens the mixture and helps to get it firm.

III.16.4.4. Discussion/Interpretation:The sugar improves the setting of the foam, its homogeneity and the regularity of bubbles. It gives a shiny and smooth effect.

At t + 72h, the foam sets but starts to fall down; also, big bubbles (diameter > 4 mm) appear. Nevertheless, such preparations are only done before the service, their use several hours later is not possible for the restaurant. To save time, the preparation can be however prepared in advance, kept in the fridge.

Recipe of a lemon gelled foam of the restaurant:

• 2 l of tap water

• 2 kg of caster sugar

• 1 l of fresh squeezed lemon juice

• 70 g of gelatine (3.5 %)

• Make 1 l of syrup with the sugar and the water by reducing the mixture by half.

• Add the lemon juice and the gelatine into the hot syrup, cool in at room temperature and whisk it cold.

The pastry cook masters this technique, thus the transfer of this principle is totally practicable for the team of the restaurant.

Making foam with a cold solution seems practicable, but the final result is not as foamy as expected. Indeed, whisking a cold mixture is less efficient than whisking a hot mixture on ice. In terms of quality, this technique is not really interesting.

This recipe was put online on Pierre Gagnaire's website, in "recipe of August", where Pierre Gagnaire cites my participation (appendix X).

III.16.5. Highly seasoned foam:

III.16.5.1. Objective:We would like to obtain jellified foams that we can cut into different shapes. Here, we try to get salted jellified foam with the taste of hot pepper. As a matter of fact, gelatine and foam lower taste. The idea is to temper a hot and spicy taste, such as hot pepper, by the means of jellified foam.

III.16.5.2. Materials and method:

• 1 dried hot pepper (10 g are infused in 500 g of boiling water).

• 200 g of the hot peppers infusion, filtered in a conical strainer.

• 5 g of gelatine,

• 2 pinches of salt

The protocol is the same as in the previous experiments.

III.16.5.3. Results:With 200 ml of water with 5 g of gelatine (solution at 2.5 % of gelatine), the mixture allows to make about 1.5 l of jellified foam after whisking 25 min (on ice). This foam is not firm enough and some bubbles (their size can reach 4 mm of diameter) can appear when you stop whisking.

III.16.5.4. Calculations: use of the formalism of dispersed systems.

III.16.5.4.1. Bubbles of the jellified foam:Let Vi be the initial volume of the solution that is used to make the foam. Let Vf be the final volume of the foam.

The size of a bubble in foam (made with a fork) is, by hypothesis, equal to 10⁻⁴ to 10⁻⁵ m of diameter.

Let Sb be the surface of a bubble (in foam):Sb = 4 π r²

Let Vb be the average volume of a bubble:Vb = 4/3 π r³

Let Nb be the average number of bubbles in Vf:Nb = 3(Vf – Vi) / (4 π r³)

Numerical application for our example:Vi = 0.2 L = 2·10⁻⁴ m³Vf = 1.56 L = 1.56·10⁻³ m³r = 5·10⁻⁵ mNb ≈ 5.16·10¹²

III.16.5.4.2. The fibres of collagen:The collagen is a protein from cartilaginous and muscular tissues. In muscular tissues, the collagen represents between 20 and 25 % of the total proteins.

The collagen is made of a triple peptidic chain, among which each possesses a helical structure and form a triple helix by hydrogen bondings.

There are two possible arrangements of these three chains, giving a "collagen 1" and a "collagen 2".

M = 30 000L = 280 nm = 2.80·10⁻⁷ mDiameter = from 1.4·10⁻⁹ m to 1.5·10⁻⁹ m

The gelatine is a gel made of water dispersed in a network of collagen, which is a solid continuous phase. Between 60 and 65 °C, the collagen splits up and the triple helix is then destroyed and a big protein network is created. By cooling, the "simple" proteins are connected together and form a protein network, which keeps a continuous structure.

A protein is constituted by amino acid (AA). If we know the amino acid length, we can deduct the length of a protein, in particular, the collagen. Indeed, an amino acid is connected with another one by a peptide link. By neglecting the influence of the radical, we can say that an amino acid has the length of a carbon-carbon link, and of a peptide link: both of a length of the order of 1.5 Å.

The length of an AA, on a polypeptide chain is thus of the order of 5 Å, is l = 5·10⁻¹⁰ m. By estimate, we can assimilate an essential molecule of collagen to a chain constituted of N = L/l amino acids.

Proteins can have various sizes due to the properties of the radicals of each amino acid. We shall thus estimate the two extreme shapes that a polypeptide chain can take; namely a thread for the most developed shape and a cube of linked amino acids for the most compact shape.

If we take this molecule in its most compact shape, it would have a shape of cube of edge equal to n. One of the faces of this cube would cover the surface of our air bubble.

S_min = ((n^(1/3))·l)² = (L/l)^(2/3) · l²

Also, the most free shape would form a network of fibres of collagens, like a square of L² of surface:S_max = 1/2 · L²

The number of molecules of collagen necessary to create a foam bubble is thus:n(c1b) = Sb / S

Let Nc be the number of bubbles which can be made using all the molecules of collagen of the solution:Nc = m_c / (M_c · n(c1b))

With S_min, we can get Nc_min:Nc_min = m_c / (4 M_c π r² L² l^(4/3))

With S_max, we can get Nc_max:Nc_max = m_c / (2 M_c π r² L²)

Finally, if Nc > Nb, then the solution contains enough gelatine to form all the bubbles of foam.

III.16.5.4.3. Calculation:L = 280 nm = 2.8·10⁻⁷ mr = 5·10⁻⁵ mm_c = 2/100 · 200 = 4 gM_c = 3·10⁴ g·mol⁻¹l = 5·10⁻¹⁰ m

Nc_min ≈ 3.4·10²⁷Nc_max ≈ 2.7·10¹⁵

In this example of foam, Nc_max and Nc_min are > Nb, thus the quantity of gelatine introduced into the solution was enough to disperse the totality of the bubbles of our foam in the solution.

The volume of foam is smaller than the theoretical maximum volume, that can be explained by a lack of water or the possible presence of fats, particles, etc.

III.16.5.5. Discussion:The foam sets, but its texture is too light to be able to be suitably cut. The mixture is very unstable and the foam possesses big air bubbles (size reaching 3 to 4 mm of diameter). If the gel of gelatine is put in the fridge, the gel would set and be firm.

In terms of taste, the infusion of a big hot pepper doesn't give a taste strong enough. However, an infusion of 1 big dried hot pepper and 2 small very strong hot peppers (finely chopped) in 500 g of water gives an enough strong taste, in the Chef's opinion.

Also, to get a lighter solution, we try to introduce a minimum quantity of gelatine into the tasty solution.

III.16.6. Sugar in the highly seasoned preparation:

III.16.6.1. Material and method:

• 300 g of infusion of hot peppers,

• 6 g of gelatine

• 100 g of sugar.

Same method as in the lemon foam.

III.16.6.2. Results:The foam sets, its texture is similar to the one of the lemon foam.

III.16.6.3. Discussion/Interpretation:In mouth, you get at first a sweet taste, directly followed by the hot of the pepper: this attack is sudden and intense.

The hot part of the pepper taste is indeed weakened in this gel. However, to the Chef's point of view, the customers can't appreciate this foam, because the first sweet taste does not warn about the spicy and hot taste of the pepper.

Furthermore, the tests made with the electric whisk don't give good results because the quantity of the samples was too small. To improve the whisking of small quantities, we can whisk by hand to use all the mixture.

III.16.7. Making of foams with a hand whisk:

III.16.7.1. Material and method:

• 250 g of infusion of hot pepper.

• 20 g of sugar.

• Gelatine.

The same method is used, but solution is hand whisked. Various concentrations of gelatine are tested (4.5 %; 3.5 %; 2.5 %; and 1.5 %).

III.16.7.2. Results:The table of results and the observations for each concentration of gelatine is in Appendix 14.

III.16.7.3. Discussion/Interpretation:With a hand whisk, the foam is more homogenous.

On ice, the liquid, which becomes foamy, sets in foam: the foam of the top gets homogenous with the liquid and forms thicker and more coloured foam. Once set in foam, it is important to give the desired shape to the foam and to keep it in the fridge.

The tests with a foam at 2 %, 2.5 %, 3.5 % and 4.5 % show that the foam thickness increases and the volume of the air bubbles decreases when the amount of gelatine introduced decreases.

At 1.5 % of gelatine, the foam is formed but doesn't set. For small quantities of solution, the best tool is the hand whisk. Otherwise, the electric whisk can be used.

At 2.5 % of gelatine, the foam is homogeneous and liquid before being cooled in cold storage (+3 °C). The bubbles we want to obtain appear with a diameter of 3 to 4 mm of diameter.

At 3.5 % of gelatine, the foam is homogenous; it sets but is however less foamy i.e. the bubbles are smaller (1 to 2 mm of diameter). The mixture is very firm and not liquid. Once put in the fridge, it becomes firmer and looks more like a gel than a foam.

At 4.5 % of gelatine, the mixture is too viscous and a part of the solution can't be whisked in foam.

III.16.8. Technology Transfer to the menu:

The restaurant applied this method of a gelled foam (G/W)/S in a dish made of an infusion of aromatic plants, which gives a cool and smooth effect to the dish.

III.16.8.1. Recipe of the infusion used in the gelled foam.

• Mint.

• Balm.

• Chive.

• Parsley.

• Coriander.

• Tarragon.

• Salt and pepper.

This infusion is filtered and a solution of gelatine (10 sheets (about 20 g) for 1 liter of water) is added. A parsley puree, which gives a beautiful green colour to the mixture is added and we start to whisk the solution in a mixer. Then, we whisk the mixture with hand, on ice.

III.16.8.2. Meeting with Pierre Gagnaire:According to Pierre Gagnaire, the foam is too thick, and the quantity of air bubbles is not important enough. We tried to whisk again the foam but the air bubbles didn't stay in the solution. We looked after which factor has an impact on the foam texture.

We tried to set foam without adding some chlorophyll. The foam mass was 169 g and its volume was 11 x 8 x 4.8 cm = 422.4 ml. This foam had a good texture, but was not satisfactory in colour. Furthermore, the same solution, whisked by hand gave a better result in terms of texture; lighter and more foamy, as wanted by the Chef.

Also, we tried to set a foam with some chlorophyll (one tablespoon). The foam mass was 170 g and its volume was 11 x 8 x 2.3 cm = 202.4 mL. This foam was heavy and contained eight times less air bubbles than the former.

III.16.8.3. Discussion/Interpretation:

• Is the chlorophyll responsible for heaviness of the foam?

• Of what is constituted this chlorophyll? The chlorophyll is a lipid (oil droplets are observed at the surface).

• Are additional proteins added? (from the white stock?)

• The chlorophyll is important for the colour of the infusion, but its quantity has to be small in order not to make the foam fall down.

• Is the chlorophyll totally needed? Can't we infuse the parsley with the other aromatic herbs? Can we use a green food colouring agent instead?

III.16.9. Conclusion:This technique is now mastered by the team of the restaurant and goes perfectly with the ingredients of the dish from the "Menu fraîcheur".

III.16.10. Other suggestions openings, ideas, applications of the technology:Is it possible to foam such a preparation with a gas spray?

III.17. Leaves of salad flavoured with methyl cellulose

III.17.1. Objective:The aim of this experiment is to make films of methyl cellulose in order to decorate a salad for example or to improve the texture of the strawberry agar-agar.

III.17.2. Introduction:The gels of cellulose set and solidify with a loss of water, thus with a rise of temperature. The films of methyl cellulose were implemented by Rachel Edward-Stuart (the Fat Duck restaurant), during the INICON meeting in June 21st, 2005.

III.17.3. First test

III.17.3.1. Material:

• 100 g of fresh squeezed lemon juice.

• 100 g of tap water.

• 50 g of squeezed orange juice.

• 50 g of caster sugar.

• 1.5 g of methyl cellulose.

III.17.3.2. Method:

1. Mix in hot water (40 °C) the mixture sugar + methyl cellulose.

2. Add the cold juices, without whipping but stirring.

3. Pour a tablespoon of the final mix on a marble.

4. Roll the solution to obtain a film.

III.17.3.3. Results:The films of methyl cellulose do not set, they do not harden after rolling.

III.17.3.4. Discussion/Interpretation:The film of methyl cellulose doesn't set at room temperature, but at a temperature < 10 °C and also, lemon juice may have its importance in this problem.

One week later, the cellulose seems to have formed a thick gel at the bottom of the bowl. Heated, mixed again, then let apart, the mixture is again thickened, two weeks later. However, no film can be realized with this thickener solution. It may be necessary to let the mixture dry in the air much longer, in order to evaporate more water or the concentration has to be increased.

III.17.4. Second test with the methyl cellulose

III.17.4.1. Material:

• 200 g of tap water.

• 2 g of methyl cellulose.

• 8 g of sugar.

III.17.4.2. Method:

1. Mix the sugar and the methyl cellulose.

2. Disperse the mix in flakes on the water and stir slowly with a spoon (without whipping) to incorporate the powder.

III.17.4.3. Results:With this cold technique, there is no problem of dissolution of the cellulose into the cold water. Again, the films do not set. However, the solution of methyl cellulose seems to gel when it is heated.

III.17.5. Third test

III.17.5.1. Material:

• 100 g of tap water.

• 1.5 g of sugar.

• 1.5 g of methyl cellulose.

III.17.5.2. Method:

1. Mix the powder of methyl cellulose with sugar.

2. Heat up 1/3 of the water until the first bubble of boiling.

3. Pour the powder of methyl + sugar in rain while moving.

4. Put it in a mixer or in a blender so as to homogenize the solution.

5. Add 2/3 of the remaining water in the mixture, continue to mix the solution during 30 min.

6. Take 10 g of solution, pour it in a Petri dish.

7. Let the solution at room temperature for 48 hours.

III.17.5.3. Results:After 48 hours of drying, a film forms in the Petri dish. Its thickness is approximately of 0.1 mm.

III.17.5.4. Discussion/Interpretation:Time of drying of the films of methyl cellulose, which were made in the previous protocols was not long enough (one hour compared to 24 hours was insufficient).

The technique works and allows to make semi flexible and very thin films. However, the texture in the mouth has a feeling of drying (like a Host). Also, in terms of the evaporation of the solution has to be considered; therefore very tasty solutions have to be used from the start.

However, these methyl cellulose films can be interesting to realize decorations.

III.17.6. Conclusion:The methyl cellulose films are remarkably interesting elements because they can be very solid even if they are very thin. They can play a role in the structural composition of a dish, as elements of decoration. Their manufacture is very simple, but it takes time to mix the solution and to dry the gel.

III.18. Emulsions

III.18.1. Objective:The Chef wanted to exploit fats from the cooking of fishes, which are very tasty. We wanted to make an emulsion with this fat, without adding the taste of an egg like in a mayonnaise.

III.18.2. Introduction:An emulsion is a dispersion of two non-miscible liquid phases.

In a mayonnaise sauce, for example, the emulsion is made with droplets of oil (dispersed liquid phase) in an egg yolk (continuous liquid phase), that possesses surfactant proteins and lecithins.

III.18.3. Example of emulsion: the butter in Kientzheim sauces:

III.18.3.1. Material:Test of Kientzheim sauces with a whole egg and some clarified butter.

• A whisk with very fine sticks (0.5 mm of diameter).

• A container (20 cm of diameter).

• Cold room (brand Dagar) with constant T °C 2 °C; precision 2 °C.

• Some tasty butter: here an orange-coloured/lemon butter and spices.

• A whole egg.

• Salt.

III.18.3.2. Method:

1. Prepare clarified butter.

2. Break the egg in the container.

3. Add one pinch of salt and homogenize.

4. Pour the clarified butter drop by drop while whipping the egg, like a classic mayonnaise. We have to shake the mixture in a same way and not to add some air into it.

5. The solution whitens gradually as we introduce the butter.

6. When the mixture is set and viscous, cool it in the fridge about one minute. Thus, the mixture will become more firm and we can then add the rest of the clarified butter.

III.18.3.3. Results:This emulsion is less firm than a classic mayonnaise. According to the Chef, the taste of the egg is too strong and the taste of the butter not enough highlighted. Two solutions can be possible: either to get bigger fat droplets (using a fork) or to use an alternative to the egg.

III.18.4. Example of emulsion: the butter in Kientzheim without the taste of the egg yolk:

III.18.4.1. Introduction:If we want to increase the flavour of the fat phase, it is necessary to disperse smaller fat droplets in the other liquid phase: the use of a hand mixer instead of a whisk is useful.

In order to study this phenomenon, we make a traditional mayonnaise and divide the mixture in two parts: one will be whipped with a fork and the other one with a Blender (Robot cuts GT 550). The flavour is modified: with the use of the fork, we get more the butter taste, while with the use of the blender, we get the taste of the egg. Thus, the difference of the fat droplet size (from 10⁻⁴ to 10⁻⁵ m with the fork) modifies the taste of our mayonnaise.

If we want to remove completely the taste of the yolk, we need to use another liquid phase that contains proteins with surfactant properties. H. This proposed many years ago to do this experiment with an egg white (that has almost a neutral taste) and also with a solution of gelatine.

III.18.4.2. Material:

• A whisk with very fine sticks (0.5 mm in diameter).

• A container (20 cm of diameter).

• Cold room (brand Dagar) with constant T °C 2 °C; precision 2 °C.

• Some butter.

• Water.

• Gelatine Rousselot (leaves).

• Egg white.

• Salt.

III.18.4.3. Method:

1. Make some clarified butter.

2. Make a solution of gelatine at 20 %.

3. In a container, put either 20 g of the gelatine solution or 20 g of an egg white.

4. Add one pinch of salt and homogenize.

5. Pour the clarified butter drop by drop while whipping forcefully, like a classic mayonnaise.

6. The solution whitens gradually as we introduce the butter.

7. When the mixture is set and viscous, cool it in the fridge about one minute. Thus, the mixture will become more firm and we can then add the rest of the clarified butter.

III.18.4.4. Results:The Kientzheim with a solution of gelatine (approximately 2 g for 10 g of water), gives a good result.

III.18.4.5. Discussion/Interpretation:In the recipe, we used some clarified butter because the solid phase that we removed may perturb the setting of the emulsion and also the final appearance. The clarified butter gets solid after approximately half an hour and hardens in the fridge.

This recipe of Kientzheim is appreciated by the Chef, for its taste, its lightness and its sweetness. (1.8 g of gelatine in 20 g of water is a solution of approximately 20 % of gelatine). Only the taste of the butter is indeed felt. Other classic mayonnaises (with eggs and oil) are firmer, but with the recipe of Kientzheim the Chef can make an emulsion with cooking fats, which are tasty.

To avoid a taste alteration by the yolk, gelatine or egg white can be used. These ingredients, tasteless, give good results and don't interfere with the taste of the fat, used into the emulsion. The results obtained with some gelatine or with the egg white are similar but the interest of working with egg white is that egg white starts to foam at the beginning of the emulsion. This particularity permits to make the dispersion of the fat phase easier.

III.18.5. Find the quantity of proteins to be incorporated into the aqueous phase to make a success of the emulsion:

III.18.5.1. Material:

• A whisk with very fine sticks (0.7 mm in diameter).

• A container (20 cm of diameter).

• Cold room (brand Dagar) with constant T °C 2 °C; precision 2 °C.

• Some unsalted butter.

• Water.

• Gelatine.

• Salt.

III.18.5.2. Method:

1. The same procedure as previously is used; the experiments were realized with different solutions of gelatine, respectively 10 %, 8 %, 7 %, 6 % and 5 % (w/w).

2. We measured the maximum quantity of butter, which can be incorporated into the solution of gelatine, giving a good setting of the emulsion.

III.18.5.3. Results:With a solution of 10 % of gelatine, the mixture sets, but it congeals when it is put in the fridge. Also some lumps appear when we whip it again. The emulsion, made with this solution possesses the same characteristics as the emulsion with a solution of 20 % of gelatine.With a solution of 5 % of gelatine, the mixture doesn't set. (3 tests)With a solution of 8 % of gelatine, the mixture sets with a good texture, and is very firm. (We can turn the bowl upside down and the mixture doesn't fall).

The table of data of the emulsion with 8 % of gelatine with some clarified butter is in Appendix 15. With a solution of 7%, the mixture sets.

III.18.5.4. Discussion/Interpretation:Once set, this emulsion is very stable, and it is showed that a big quantity of clarified butter can be added. The mixture hardens once put in the fridge (note that it is necessary to use a solution of gelatine, cooled at room temperature and not in the fridge).

The use of gelatine doesn't induce texture changes of the mayonnaise. Indeed, the initial texture of mayonnaise is easily obtained after whisking the mixture back at room temperature.

III.18.6. Conclusion:An emulsion of any fat, done with either an egg white or a solution of gelatine, is much more tasty (in terms of that taste of the fat used) than a traditional mayonnaise, using a yolk. This technique is easy to realize, because the tools and the way of doing it are similar to a classical mayonnaise. Also, it takes about a quarter of an hour to prepare it, and it can be done in advance and stored in the fridge. In the case of the butter, only its structure is modified, but it keeps all its properties, and then, it can be stored as a classic butter.

III.18.7. Other suggestions, openings, ideas, applications of the technology:We can also use a tasty aqueous phase in order to disperse the gelatine, instead of water as used in these experiments.

III.19. Meringues with egg white powder

III.19.1. Objective:Realize a flavoured meringue from a tasty juice or puree, salty or sweet.

III.19.2. Introduction:Replace the contribution of water of the egg whites by a tasty liquid. For that purpose, it is necessary to introduce proteins, which possess the same properties as those of the egg whites. The egg white powder (freeze-dried egg white) used in food industries was then used and completed with a tasty liquid.

III.19.3. Case of sweet meringues:

III.19.3.1. Material:The recipe comes from Hervé This's works about the egg white powder and fruit and vegetable juices.

See Appendix 16: Etude sur la gastronomie moléculaire lors de la formation IUFM au lycée hôtelier d'Orchies.

• 200 g of fruit puree (here a melon puree).

• 300 g of caster sugar.

• 20 g of egg white powder, supplied by Louis François.

• 2 g of cream of tartar, food additive E336, supplied by Louis François.

• Electric robot, brand Kitchen Aid (10 levels of speed).

III.19.3.2. Method:

1. In a container, put the juice to be built up in meringue.

2. Mix the egg white powder with its volume in sugar and the cream of tartar.

3. Start the electric whisk at speed 1, (classic meringue whipping). Pour the powder slightly in the container (the powder is very fine and very volatile) in order to incorporate it into the juice.

4. Once the mixture is homogeneous, (the first bubbles start to be formed and the mixture gets lighter) put the level 5 and make a classic meringue.

5. Add the sugar when the mixture is set, always by sprinkling.

6. Beat the mixture until obtaining a brilliant, smooth and firm mixture. About 12 min.

7. Make meringues by means of a piping bag and arrange them on a buttered plate.

8. Cook 1h30 in a ventilated oven at 100 °C.

III.19.3.3. Results:This technique gives very tasty meringues with the same texture as classic meringues. Meringues made with melon puree have a strong and intense flavour of melon, very pronounced.

This technique allows realizing very tasty meringues with any juice or puree, without fat, which would bring down the foam. Furthermore, the thickness of the juice plays a role on the final texture of the meringue: thicker is the juice, thicker is the meringue.

III.19.4. Salty meringues:

III.19.4.1. Material and method:Recipe of the "snow of tomato"

• 200 g of tomato juice (a coulis of tomatoes with spices, cooked for 2 hours)

• 20 g of egg white powder

• Electric robot, brand Kitchen Aid (10 speeds)

The same method as above is applied to do this recipe of salty meringues.

III.19.4.2. Results:The whisked mixture rises quickly but also falls down rapidly. It is then important to cook these meringues in the oven as soon as they are modelled. The foam is very fragile and it is difficult to give them a nice shape.

These meringues were dried in a steam oven at 40 °C before being completely cooked in the oven. Unfortunately, they weren't cooked enough and they fell down. Their way of cooking has thus to be improved. However, they had a powerful taste of the tomato juice and herbs.

To conclude, the whisked solution needs to be more viscous, in order to get firmer foam. In classical meringues, the viscosity of the egg whites is increased by adding sugar, which is hygroscopic. Another solution could be to increase the tension force at the interface between the liquid (the mixture) and the gas (the air). This would provide smaller air bubbles, implying a firmer texture.

III.19.4.3. Calculations:It is important to know the optimum quantity of egg white powder to add to get the higher foam volume. As a simple model, we can consider the solution as a mixture of water and proteins (ovalbumin is the major protein in the egg white, 58 % of the total proteins).

III.19.4.3.1. Maximal Quantity of foam made with an egg white:We want to find the maximum volume of foam made with an egg white and addition of water.The weight of one egg white is about 30 g. The proteins represent about 10 % (w), which is about 3 g.

M_ovalbumin = M_egg prot = 45 000 and 75 < M_AA on average < 200Hypothesis: M_AA on average = 132.5

The average number of amino acid residues in a protein of ovalbumin is:N = M_ovalbumin / M_AA on average ≈ 340

Ovalbumin is a protein constituted by amino acids (AA). We can calculate the length of the protein, knowing the "length" of one AA. Indeed, an amino acid is connected to another one by a peptide link. By neglecting the influence of the radical, we thus know that an amino acid has the length of a carbon-carbon link, and of a peptide connection: both of a length of the order of 1.5 Å.

The length of an AA, on a polypeptide chain is thus of the order of 5 Å, is l = 5·10⁻¹⁰ m. By estimate, we can assimilate an essential molecule of collagen to a chain constituted of n amino acids:L = N*l = 1.70·10⁻⁷ m

Proteins can have various sizes due to the properties of the radicals of each amino acid. We shall thus estimate the two extreme shapes that a polypeptide chain can take; namely a thread for the most developed shape and a cube of linked amino acids for the most compact shape.

In its most compact shape, such molecule would have a shape of cube whose edge is the cube root of n. The surface of the air bubbles would be covered by such cubes.S_min = (((L/l)^(1/3))·l)² = (L/l)^(2/3) · l²

Also, the most free shape would form a network of fibres of collagens, like a square of L² of surface:S_max = 1/2 · L²

The total surface of bubbles that can be covered by the proteins of gelatine is thus determined by the number of structural units of collagen by the total surface considered:Let S_m be the surface covered with the most compact shape of collagen. Let S_M be the surface covered with the less compact shape of collagen.S_m = n/M · (((L/l)^(1/3))·l)²S_M = n/M · 1/2 · L²

III.19.4.3.2. If we consider that the gas is dispersed in a single bubble:If we consider that only one air bubble is created with the proteins to disperse the maximum quantity of fat, the equation S would be:V_m = 4/3 · π · (m/M · (((L/l)^(1/3))·l)²)^3V_M = 4/3 · π · (m/M · 1/2 · L²)^(3/2)

With m = 3 g and by multiplying by the number of Avogadro:V_m = 6.78·10⁸ m³, which represents a bubble of 100 m of diameter.V_M = 8.17·10¹⁵ m³, which represents a bubble of 100 km of diameter.Note: V_m < V < V_M

III.19.4.3.3. If we consider that the air is dispersed in several bubbles:We can find the created volume by dividing the surface covered by our proteins by the surface of a bubble, we find then the maximum number of formed bubbles. By multiplying by the volume of a bubble, we so find the volume of air dispersed in the foam:

Vb / Sb = 4/3 · rV_m = m/M · (((L/l)^(1/3))·l)² · 4 · r / 3V_M = (2 m L² r) / (3 M)

With m = 3 g and by multiplying by the number of Avogadro:V_m = 8.71 m³V_M = 309.0 m³Note: V_m < V < V_M

III.19.5. Conclusion:This technique allows to heighten the taste of meringues, and to give a flavour to these without the need to add a liquid to the preparation. Indeed, the tasty solution replaces the water found in the egg whites.

These meringues can be perfumed with any taste of an aqueous solution. The use of fat is impossible, because the foam would fall down. In the case of salty meringues, the technique works, and the meringues are tasty. However, this texture has to be improved.

III.19.6. Other suggestions openings, ideas, applications of the technology:We can use this technique in recipes where egg whites are used, such as omelettes, cakes...

III.20. 6X°C eggs

III.20.1. Objectives:Determine the time of cooking of an egg at 65 °C.

III.20.2. Materials:

• An egg, of average size.

• A Steam oven, brand MODULAR SALVA (Precision 3 °C) fixed in 40 °C.

• Thermocouple MAFTER typifies K, range 50 – 950 °C; precision 1 °C, with a needle as a tip of measure.

• Bag of preservation for food under vacuum.

• Machine to put under vacuum brand Multivac / Gastrovac. T °C 0 – 100 °C; a Graduation 0–10; 2 bars of pressure.

• Chronometer with a precision of one second.

III.20.3. Method:

1. The egg is put under vacuum, in a bag of preservation, intensity 4 of the machine.

2. Stay in the steam room.

3. We measure the temperature inside of the egg by means of an electric thermometer, (we use the needle in the heart of the egg, the hole of the shell is made waterproof by a pastille) and we estimate the time of rise of the internal temperature of the egg until it reaches the temperature of the steam room.

III.20.4. Results:The egg, placed in a steam room at 65 °C under vacuum, is cooked after 34 min and 8 s very exactly.

III.20.5. Discussion interpretation:No fluid escaped from the egg, this showed that the egg remained hermetic during the experiment. Comparing to a classical egg at 65 °C, this egg has the same gustative properties (a test panel was realized by the team of the restaurant).

Now, these 65 °C eggs are cooked in the restaurant for two hours (in the same vapour oven). However, the eggs are placed in a stainless steel tub, and they are submerged in water, in order to homogenize the heat distribution.

The time of cooking of this experiment is thus bigger than the time of cooking of a submerged egg in water, but with these data, we are sure that eggs are all cooked correctly.

III.20.6. Evaluation:Reliable method of measuring the cooking time.

III.20.7. Conclusion:For the Chef, this experiment supplies a precise datum of the cooking time of 65 °C eggs for his vapour oven, and this allows to save a lot of time. Indeed, before this experiment, 65 °C eggs were cooked during 2 hours but since the internal temperature of the egg is the one of the oven, this temperature doesn't change significantly. This means that in terms of taste and texture, there are no differences between a 65 °C egg cooked during 35 min or 2 hours.

Concerning transfer from the laboratory to the restaurant:

The technology transfer made reported here had to answer the various constraints of the restaurant, not disrupting its functioning during the application of these techniques.

First of all, the material constraints of the restaurant forced to take into account the room available, the consequences of using the material and the ingredients, without disturbing the real work in the kitchen.

Human constraints meant to work with the staff considering its functioning and the way of working of the Chef. The possible training of the cooking staff to use some techniques has also to be scheduled.

Like every dish in the restaurant, the manufacture of these new dishes can't exceed 15 minutes.

Finally the possible cost of these techniques has to be considered, involving ingredients losses, and investment costs for new products or for new tools.

The Chef and his crew were not really available for common reflections on experiments. However, the bigger issue was the misunderstanding of the restaurant team between a new technology and the taste given by the new recipe. Indeed, the team of the restaurant made the association between the efficiency of a technique and the gustative effect. The adaptation of these techniques to the restaurant varied essentially according to the ability of the Chef to apply the technical principle. Thus, these transfers were limited due to the Chef's unavailability during the period of this internship. However, the Chef also needs time to think about recipe, integrating these new technical "tools" for the realization of new dishes.

What should be known about culinary ingredients: Water

Water structure?Pure water is filled with water molecules which are constantly moving around. Each of these water molecules is composed of two hydrogen atoms and one oxygen atom, organised in a "V" shape as shown below.

Although this molecule is neutral, and is not charged overall, its charge is actually evenly distributed throughout its structure – the oxygen (O) atom carries a weak negative charge, whereas each hydrogen (H) carries a weak positive charge. This makes the water molecules attract one another. In water, which contains many of these molecules, the negative oxygen atom on some water molecules will be attracted to the positive hydrogen atoms on other water molecules (in a similar way to the north and south poles of magnets) and this attraction is called a hydrogen bond.

Water propertiesWhen water is heated, the molecules will start to move around with more energy and speed, so these links will start to break, freeing the water molecules, and some of these water molecules will escape (this is water vapour). At 100 °C, all these links are broken - so water is no longer a liquid and it becomes a gas. In contrast, when water is cooled, the water molecules will have less and less energy to move around, so will form even more bonds with each other. The water molecules will be no longer free to move, so the water will become solid. This is ice.

Water molecules will always move in a direction from where there are more water molecules to where there are less, if it can, by a process known as osmosis. For example, if a strong coffee is added to a glass of water, the large number of water molecules in the water will redistribute themselves evenly in the coffee, and the resulting solution will be an evenly distributed mixture of coffee and water...or a much weaker coffee!

Solubility in water:Molecules are often classified by how they interact with water. Molecules that like to interact with water are called "hydrophilic", or water-loving. These molecules like to interact with water because, like water, they are charged, so are attracted to the water molecules and can form links with them. This is what occurs when a substance "dissolves". For example, when salt is added to water, it will dissolve. Salt is made of Na⁺ ions and Cl⁻ ions held together, and in the presence of water, these ions will separate and be attracted to and form bonds with the water molecules. Because the salt has been split into individual Na⁺ and Cl⁻ ions, it is no longer visible to the naked eye because the separated ions are too small. However, if the mixture is heated to evaporate all the water, only the Na⁺ and Cl⁻ ions will be left, which will then be free to rejoin with each other to form the original salt.

The boiling point of water can be changed if substances are added to it, depending on the relative boiling point of the added substances. For example, water will boil at a slightly higher temperature if salt is present because salt has a much higher boiling point than water. The more salt contained in the water, the higher the boiling point of the solution. However, if alcohol, which has a boiling point lower than that of pure water, is added to water, it will decrease the boiling point of the final mixture.

The freezing point of water is also changed by adding substances to it, however all substances added to water will act to decrease its freezing point. This is because any other substance present will act to get in the way of the water molecules as they try to make bonds with each other to form ice, so temperatures lower than freezing are required to freeze the water.

This explains why salt is often added to ice on the roads to encourage it to melt – it causes the ice to melt at a lower temperature.

Non-solubility in water:Many molecules however do not interact with water. They are called "hydrophobic", or water-hating. These molecules are neutral, and do not interact with water because they are not attracted to the water molecules, so they will not preferentially mix.

For example, oil does not mix with water. This can easily be seen if oil is added to water, the oil (which is less dense) will float to the top and not mix with the water. The hydrophobic oil molecules will "stick together" with special bonds (called hydrophobic interactions), and the hydrophilic water molecules will "stick together" due to the hydrogen bonds.

If the mixture is vigorously shaken, the force of shaking will break the two liquids into smaller droplets, and the tiny droplets of oil will temporarily disperse in the water. However, as soon as this force is stopped, the oil droplets are free to move around and combine, and as the droplets become bigger again the two layers separate out.

In order for a mixture of oil and water to stay stably dispersed, a special sort of molecule needs to be added. These molecules are called tensioactive molecules. They possess a hydrophilic head and a hydrophobic tail, or in simpler terms they have one end of their molecule that is soluble in water, and one end that is soluble in oil. The principle is that these molecules surround the tiny oil droplets by making contact with their hydrophobic parts, leaving their hydrophilic parts to contact the water part and keep the fat droplets very dispersed. Many foods contain such tensioactive molecules which are commonly used to stabilise oil/water mixtures.

Role in food:Water is the most abundant molecule in nature. Most foods contain primarily water (e.g. vegetables contain very high amounts of water, as do meat and fish, and dairy products like milk and eggs). Many of these substances therefore lose mass if they are cooked at high temperatures, because the water contained will evaporate, making the cooked mass less than the raw mass.

In food, water is often perceived as "tenderness". Hard cheese contains much less water than soft cheese, and is therefore less tender. A rare steak (where little liquid has been evaporated during the short cooking time) is much more tender than a well-done steak (where water evaporation is much more significant).

More about culinary ingredients: Meat

Meat compositionMeat contains water (about 75%), proteins (about 20%) and fats (normally only around 3%). In a piece of raw meat, however, the arrangement of these substances is much more highly organised than in for example a raw egg white (which just contains a simple unstructured mixture of proteins and water molecules).

Its contents are essentially organised into three different sorts of tissue.

• The muscle tissue: This is the main tissue, and is composed of many muscle cells, or fibres, containing the muscle proteins actin and myosin. These muscle proteins and fibres are responsible for how an animal moves when it's alive, and how tough the meat is to eat once the animal is dead. As an animal grows and exercises, the muscle tissues strengthen and become thicker – meat from an older animal is tougher than meat from a younger animal.

• The blood: The muscle tissue also contains blood vessels that contain the pigments responsible for the colour of meat. The main pigment (comprising 75% of the total pigment content) is called myoglobin, which contains a central iron atom attached to a large protein. In the presence of oxygen, the iron atom "holds" the oxygen molecule and appears bright red. The more a muscle is used, the more of this pigment it will need, so the redder the muscle will be, so the parts of the animal that use its muscles a large amount (e.g. the legs) will be darker in colour and tougher (contrast chicken breast with leg, and how tender the appropriately named "tenderloin" is).

Not all meat is red. Some animals are made of "white meat", such as chickens and poultry. This is simply because their muscles are arranged in a different way to "red meats", and their myoglobin levels are lower, giving them a lighter colour. This is because poultry, which tend to move in short rapid bursts, have different muscle requirements to a large cow, which must support his body weight all day, and he tends to have muscle of the red sort.

• The connective tissue: The muscle tissue is found surrounded by connective tissue, which acts as a glue to stick the muscles to the bones and also limits the proteins responsible for muscle contraction. The connective tissue is composed of strong fibres made mainly of the proteins collagen and elastin. Collagen is a stiff protein, composed of three long chains twisted round each other like a rope. The presence of large amounts of collagen tissue in a piece of meat makes the meat tough. Equally, the connective tissue thickens and toughens as an animal gets older, increasing meat toughness. Fortunately, the major protein in the connective tissue, collagen, can be partly dissolved on cooking at temperatures over 55 °C to form gelatine, which helps to tenderise the meat. Elastin however does not tenderise on cooking, but actually shrinks and hardens. It therefore needs to be removed from the meat before the meat is cooked, usually by cutting it out with a sharp knife.

• The fat tissue: Between these two tissue types is the fat tissue – the fat tissue is seen as dispersed white patches in the muscle tissue. Young animals tend to have smaller amounts of fat in their meat than older animals. The fat tissue will melt on cooking, lubricating the muscle fibres, making it easier to chew between them. The fat tissue has an important role on the taste, since most of the aromas in meat are hydrophobic, so are dissolved in the fat part.

Meat textureRaw meat is therefore not very tender, especially when taken from older animals, or from muscles that are used often, due to the strong muscle fibres and the tough collagen fibres.

Meat can also to an extent be tenderised by heating – long heating causes breakdown of the tough collagen tissue and the melting of the fat that lubricates the strong muscle fibres. However, heating also causes the meat proteins to denature and coagulate, and long cooking times at high temperature will cause this network to tighten, and the meat to squeeze out some of its juices making the meat dry. Therefore, meat is often tenderised before cooking by ageing or marinating meat because it will reduce the need for long cooking times, which cause strengthening of the protein network, and toughening of the meat.

Tenderising meat: Meat can be naturally tenderised by leaving it to age. After an animal has died, enzymes it naturally contains will start to attack everything that they can. During the first few days, internal proteolytic enzymes in the meat start to partially hydrolyse the muscle fibres, loosening them, and starts to degrade the muscle proteins, softening the meat. After approximately a week, enzymes begin to break down the collagen protein in the connective tissue, which increases the tenderness, and allows the collagen to be more readily converted into gelatine during cooking.

As well as reducing toughness, ageing improves the taste because the amino acids produced by partial protein degradation are more flavoursome than the original proteins. Other of the meats enzymes are involved in improving the taste – fats are converted into aromatic fatty acids by the lipases present. All of these molecules improve the taste of the meat, and additionally provide more substrates for the Maillard reactions that may subsequently occur on cooking the meat to further aromatise and flavour the meat.

These tenderising enzymes act more quickly as temperatures are increased to around 50 °C, so will continue to act as the meat is heated up. However, as temperatures reach over 50 °C, these enzymes are denatured and will no longer be able to act.

Tough meat can also be artificially tenderised in a number of ways:

• Physical – mincing or hammering the meat breaks up tough connective tissue and strong muscle tissue into smaller more digestible pieces. Meat can also be tenderised by slicing the meat into smaller pieces, which makes the collagen fibres and muscle tissue smaller and weaker and easier to break apart. Sometimes slithers of fat are inserted into tough cuts of meat before cooking – this breaks up some muscle fibres and connective tissue as the fat is inserted, as well as increasing the fat content, that reduces perceived toughness.

• Chemical – this is most often carried out through marinades. Marinading a meat before cooking reduces subsequent cooking times.

There are three classes of marinade:

• Acids, like lemon juice, vinegar, wine or tomatoes, helps tenderise meat by starting to denature the proteins, causing them to unwind. Since one of the aims of cooking is to denature the meat proteins (which makes the meat more digestible), marinading first will reduce subsequent cooking times. However, marinades penetrate meat very slowly, so the proteins in the outside of the meat, that are in direct contact with the marinade, may start to coagulate, and as the bonds in the protein network start to strengthen the meat juices may be forced out. This problem can to some extent be prevented by injecting the marinade into the centre of the meat, using a cook's syringe.

• Enzymes: some raw fruits contain protein-splitting enzymes (proteases), which act on raw meat to tenderise it. They work in the same way as natural ageing by breaking down and softening the muscle fibre and connective tissue (collagen), making the meat less tough. Examples of these protein containing fruits include the pineapple, the papaya, the pawpaw, kiwifruits, or figs. All these enzymes work fairly slowly at room temperature, but work very quickly between 60 and 70 °C, so have most effect on tenderising the meat at the beginning of the process of cooking the meat. These enzymes penetrate the meat even slower than marinades, so often the outside of the meat may become overly digested and tender while the inside of the meat remains tough. Again, injecting these enzymes into the centre of the meat avoids this problem.

• Dairy: Dairy products such as buttermilk or yoghurt are only mildly acidic, so do not toughen the outer part of the meat in contact with the marinade in the way that the strongly acidic marinades do. Additionally, it seems that the calcium in dairy products activates enzymes in meat that break down proteins, tenderising the meat like ageing does.

Preserving meat

FreezingFreezing turns the liquid within the cells into frozen crystals. The formation of these sharp angled crystals can break a delicate wall such as a cell membrane pretty easily and quickly. Then as the meat subsequently thaws, the contents of the cell seep out.

The thawed meat is therefore more likely to dry out during cooking, because it has a lower initial water content. This also explains why multiple cycles of freezing and thawing causes much greater moisture losses. Freezing should be carried out as quickly as possible, since when ice crystals form quickly, they remain tiny.

Meat should be well aged before freezing, since meat does not continue to tenderise when frozen.

BriningDuring brining, meat is placed in a very strong salt solution. This has several effects:

• Firstly, the salt will slightly disrupt the muscle tissue. The salt ions locate themselves between the denatured protein strands, and it will therefore form a much looser network on coagulation, so the result of moisture loss due to syneresis is reduced.

• Also, as the salt and any other flavours penetrate the meat cells, the cells will absorb water from the brine, and its mass will increase. This also helps to tenderise the meat because when the meat is cooked and the juices are squeezed out, the meat will appear less dry due to its higher initial water content, and the meat will appear more tender. It is the outer layers that will absorb the most liquid, and it is also these outer layers that would normally tend to dry out most during cooking.

• It helps improve the taste by amplifying all the flavours of the meat.

• It acts as a preservative, by providing conditions unfavourable for bacterial growth.

Salt has the disadvantage of affecting meat colour. Salt will help to oxidise myoglobin, converting it from the bright-red coloured pigment to metmyoglobin, which is slightly brown coloured.

Cooking meatUnlike the other food ingredients, meat is almost always cooked before it is consumed. Meat is cooked for the following reasons:a) to kill bacteria and make the meat safe to eatb) to make the meat more digestible (denatured proteins are more easily digested than folded proteins)c) to improve flavourd) to reduce toughness (however, cooking may also increase toughness, as explained below)

What occurs on cooking?As meat is heated, the muscle proteins start to denature. This starts at a temperature of approximately 40 °C, when the highly heat sensitive muscle proteins, the myosins, start to denature. This can be visualised by the apparent loss of translucency - light can no longer pass through the gaps previously present between the individual highly-folded proteins, and the meat loses some transparency. This initial denaturation is also associated with an increase in juiciness of the meat - some liquid is liberated as the proteins unwind. As temperature increases, the other proteins present will also start to denature and coagulate. At around 60 °C, one of the last proteins denatures – this is the myoglobin, and its denaturation has a much more important effect on the colour of the meat than the texture. The myoglobin denatures to form a compound called hemichrome that is more a brown-grey colour (since it is similar to the colour change on brining meat).

So at the temperature where the meat changes colour from red to brown is to some extent associated with the temperature at which the protein network is the most "juicy", and this can be used as an indicator for the doneness of meat – meat removed from the heat just after the meat goes brown (i.e. when it is at a temperature of about 65 °C) will be tender and juicy.

With continued heat, the networks of meat proteins will start to strengthen, and water will be squeezed out of this network, which will then evaporate, and the meat will shrink. These strong protein networks make the resulting meat difficult to chew, and the meat will appear much dryer. So the longer the meat is heated, the tougher and drier it becomes. Hence a well done steak is much drier and tougher to chew than a steak cooked rare.

Tenderizing the inside without losing juices: Long low temperature cooking:So in order to keep meat moist, juicy and tender it should be cooked at temperatures no hotter than 65 °C (at which temperature strong coagulation occurs), which takes a very long time. However, cooking at this temperature has various drawbacks:

1. Temperatures of approximately 70 °C need to be reached in order for all the bacteria in meat that can cause human disease to be destroyed. Usually, if the piece of meat being cooked is whole, this is less of a problem, because the bacteria will only be located on the surface of the meat, and temperatures are highest on the meats surface during cooking. However, for minced meat, the risk is greater, and dishes based with minced meat should be well cooked to at least 70 °C throughout.

2. As mentioned above, many tough cuts of meat contain large amounts of the tough molecule collagen. The collagen in the elastic tissues will start to dissolve and form gelatine when the meat is cooked to above 70 °C. After collagen breakdown, the muscle fibres are much more easily torn apart while chewing, and the meat will appear tender. Also, the meat needs to be heated for a long time at this temperature in order to dissolve all the collagen.

3. The Maillard reactions responsible for many of the desired flavours and smells of cooked meat do not start to occur until temperatures over 50 °C are reached. The Maillard reaction involves a large number of reactions between the amino acids from denatured proteins with the sugars also present in meat. Molecules are rearranged, and new molecules are formed. These reactions can produce many different new molecules - meat contains about 20 different amino acids, and several different sugars, so the number of possible combinations is immense. The new molecules formed can either break down to form yet more new compounds, or react further with each other to produce other molecules, or even react with other meat components (like the fats) in various ways to produce even more resulting molecules. Amongst the molecules produced are the melanoidins – these are coloured and help contribute to the brown colour of cooked meats. It is the large combination of all these different molecules that gives the cooked meat its brown colour, taste and smell. The final taste perceived with a piece of cooked meat depends on the profile of all the different molecules produced, and their concentrations. For example, the aroma of roast beef contains over 600 component molecules. In general, the Maillard reaction occurs most rapidly at approximately 150–250 °C, but if there is a high concentration of sugars and amino acids, then it will occur at lower temperatures.

4. Temperatures higher than 65 °C are needed to totally melt the fat during cooking that lubricates the muscle fibres, keeping the meat moist.

So meat which is cooked at 65 °C to maximise the juiciness, has associated effects that may not be favourable. The meat will have an elevated bacterial risk, less taste due to reduced Maillard reactions, and less fat lubrication. It will also remain fairly tough after cooking if it had a high original collagen content.

Quick high temperature cookingMeat cooked at very high temperatures will have a lower bacterial risk, more fat lubrication, better collagen breakdown, more taste; but will rapidly become tough and dry if cooking time is long.

A compromise: Often, the best compromise is to cook the meat at a very high temperature, for a very short time (to ensure bacteria are killed and that Maillard reactions can occur), and if it is a large cut of meat to finish the cooking in a very low temperature oven.

Finally, there is not one sole recommended technique for cooking all meats, like for eggs or vegetables, because different cuts of meat differ greatly in their structure and tissue composition, and thus different pieces of meats are suitable to different cooking techniques.

• The old tough cuts: Old, tougher cuts of meat that are high in collagen need to be cooked for long times at temperatures above 70 °C, despite the drying out that might also occur. However, tough cuts tend to come from older animals, and the fat content of meat tends to increase with age. Therefore it is not as serious if these meats are cooked for a long time at higher temperatures because the effect of the melted fat improves perceived juiciness and tenderness, despite the actual meat being dryer.

• The tender young meats: Tender meats however, which contain less tough collagen and strong muscle fibres, do not need to be cooked for long times at low temperatures – indeed, the best way to reduce moisture loss is to cook these pieces at a very high temperature for a very short time – this greatly reduces cooking time and thus the risk of excessive coagulation and moisture loss.

Cooking in a liquid

The benefits: Cooking meat in a liquid is an effective way of evenly transferring heat to all parts of the meat, especially compared to cooking meat over a hot solid which only heats the part of the meat in contact with it. Heat is transferred by the hot liquid molecules moving – this type of heat transfer is known as convection.

If the liquid is kept at a temperature that is well below the boil, the meat will stay fairly tender as the temperatures inside the meat are high enough for the proteins to denature and coagulate, but temperatures, even at the meats surface, are not high enough to cause significant squeezing out of the liquids trapped in the protein network and thus drying out of the meat. Cooking at a lower temperature therefore prevents the meat from being over-cooked. It also prevents any aromatic molecules, which are destroyed at high temperatures, from being destroyed.

This method of cooking in a liquid for a long time is therefore ideal for cuts of meat high in collagen. Over time, the collagen molecules will dissociate from the connective tissue and dissolve into the cooking liquid. In this form it is called gelatine, and has the ability to form a gel on cooling, if sufficiently concentrated in the cooking liquid.

Boiling:During boiling, coagulated proteins that have dissolved off the meat may clump together on the surface of the cooking liquid, where they may form a scum.

The disadvantages: However, cooking in water has two major disadvantages:

• Because the temperature of water never exceeds 100 °C, the desired flavour producing Maillard reactions cannot occur. Boiled meat therefore looks and tastes rather plain. The flavour of boiled meats is determined only by the simple breakdown products of proteins and fats, which are not as flavoursome as the Maillard reaction products.

• Additionally, flavour will be lost as some of these molecules move from the meat to the cooking water by diffusion. Water soluble mineral salts and melted fat may also move into the cooking water. The longer the meat is cooked, the more flavour is transferred from the meat to the cooking liquid, and the more the taste of the meat is reduced. The movement of all these substances into the cooking water can be prevented by flavouring the cooking liquid before the meat to be cooked is added. For example, salt in the cooking water reduces the number of mineral salts that move into the cooking water, allowing the meat to keep more of its taste. Alternatively, in order to not waste all the strong flavours that have moved into the cooking water, the flavoursome cooking liquid is often boiled down and reduced to concentrate the flavours, and then this liquid is then served with the meat. (The meat is usually removed from the liquid before the liquid is reduced to prevent overcooking and drying out the meat that might otherwise occur at boiling temperatures). Alternatively, the meat is allowed to cool in the cooking liquid itself – as meat cools it actually reabsorbs some of its lost liquid. The cooking liquid can accumulate between the fibres of the separated collagen network, and will therefore add back some of the lost taste.

Making stock: Some particularly tough collagen rich pieces of meat will need to be cooked in the liquid for a very long time to dissolve all the collagen, but these long cooking times will tend to remove practically all of the taste from the meat, but the cooking liquid will become very flavoursome. The meat used to make these stocks is usually not intended to be eaten, so the aim in this situation is to actually maximise the amount of flavour that leaves the meat and enters the liquid. In this situation nothing should be added to the cooking liquid like salt, because diffusion of the maximum amount of aromatic molecules is desired.

Braising:This method of cooking meat produces the similar desired textures that boiling does except that it increases the generation of taste.

During braising, the meat or poultry is first browned in hot fat, sometimes with vegetables. This starts the tenderisation process (by increasing the activity of the meats own tenderising enzymes), and favours the Maillard and browning reactions that produce the characteristic aromas of grilled meats.

An aromatic cooking liquid is added to the pot. The liquid is usually flavoured (i.e. not water) and normally contains vegetables and lard. A flavoursome cooking liquid reduces the leak of flavoursome molecules from the meat by diffusion. The aromatic molecules from the vegetables will move into the meat (where they are at a lower concentration) by diffusion, whereas the meats own aromas are less likely to move out of the meat by diffusion, because the meat source (i.e. the ham and bacon) present in the cooking liquid release similar types of molecules into the cooking juice, equalising their concentration.

The meat cooks in relatively low heat (usually in a low temperature oven) for a very long time. The long cooking time allows all the collagen to deform and dissolve, and the low temperature prevents the coagulated protein networks from squeezing out too much water, and prevents heat induced destruction of the flavour molecules. Covering the pot prevents the aromatic components evaporating with the water vapour and flavour from being lost.

Cooking in oil:In frying, the meat is completely immersed in hot oil. This allows an even transfer of heat like is achieved in boiling, eliminating the need to regularly turn the meat sample. However, the temperatures that can be reached on frying are much higher than those reached on boiling – the oil is usually heated to a temperature of 175 °C before the meat is added.

The oil type:Butter is not usually used for frying because it can only be heated to temperatures of 120 °C before it will start to decompose, and this temperature is not high enough for efficient frying.

Equally, the oil used for frying should only be used several times. Oil heated to high temperatures degrades, and produces a strong bitter odour due to a compound called acrolein. If the same oil is heated over and over again, the levels of acrolein become so great that the taste of it in the fried meat can be detected.

The process of frying:As soon as the meat is added to hot oil, water at the surface of the meat rapidly evaporates. Meat to be fried should therefore be dried before it is fried, or the rapid evaporation of surface water may cause dangerous explosions of the hot oil.

As the water evaporates, the surface dries, and the proteins on the surface of the meat rapidly coagulate producing the hard crunch of fried meats. The immediate forming of the crust prevents oil from penetrating the sample, which would make the piece overly greasy. The elevated temperatures reached at the meats surface allow the Maillard reactions to brown the meats surface and produce the desired taste molecules. Because temperatures are high, the meat cooks rapidly, preventing excessive drying out that occurs on long cooking times, especially at high temperatures. Therefore only small pieces of meat should be fried – the inside of the piece of meat will cook before the outer surface begins to carbonise, and the inner parts of the meat begin to dry out.

Batter:Meat is often battered before frying. The result is that it is the batter that forms the oil-impermeable crust, rather than the meats surface directly, which prevents the drying out of the meats surface that is associated with the crust formation. Poking the meat with a fork before battering allows the egg and flour mixture to penetrate the holes, better anchoring the sample to the grilled outer layer.

Batter is usually made of bread crumbs or flour, with egg. The batter will become hard and crusty as the egg proteins coagulate, and the swollen starch granules release some starch that allows the batter to remain stuck to the meat. The presence of breadcrumbs or flour increases the sugars that are present in the food being fried, increasing the rate and diversity of the flavour-producing Maillard reactions.

Cooking in a solid

Grilling and sautéing:When meat is grilled or sautéed, the meat is heated by direct contact with the hot pan. This form of heat transfer is known as conduction (or radiation if the heat source is hot enough to glow, i.e. produce light). Heating meat by direct contact with a very hot solid is not as even a way of transferring heat as immersing the meat in a very hot liquid (i.e. frying or boiling), so the part of the meat in direct contact with the heat will heat up much more quickly than the other parts. In order to ensure a more even heat transfer, the meat should be regularly turned during heating to more evenly transfer the heat.

As soon as a piece of meat is added to a hot pan, the meats surface in contact with the pan will undergo some rapid changes. The proteins will coagulate forming a crust, and the meat will start to sizzle due to the rapid evaporation of water that occurs in the surface in contact with the pan. Once the surface water has evaporated, temperatures at the meats surface can reach high enough that the browning Maillard reactions can occur very quickly and the meats surface quickly browns and develops many of the flavours associated with grilled meat.

However, the disadvantage of such high temperatures is that the meats surface may burn and blacken, and the outer parts of the meat rapidly dry out as the coagulated protein network quickly tightens and squeezes out water, before the inner parts of the meat are cooked.

The impermeable crust:Many people think that when a piece of meat is grilled, the crust that is immediately formed on the surface of the meat due to the water evaporating and the proteins coagulating acts as an "impermeable crust" that keeps all the meat juices trapped inside the meat and prevents them from getting squeezed out by syneresis. However, if this crust really does function to prevent the juices from leaving the meat, once a grilled piece of meat is placed on a plate after cooking, the juices would not be expected to leave the meat source – but they do. The juices that are squeezed out during cooking are not visible in the pan because they rapidly evaporate in the heat. This means sauces to be served with grilled meat should be made slightly thicker than is desired – the juices that leave the grilled meat after cooking may dilute the sauce.

Additionally, examination of the meat surface structure with a microscope shows that in the outer surface of a piece of grilled meat there are gaps that have formed between shrivelled up muscle cells. The outer surface is more similar to a sieve. So since the juices can indeed leave the meat during cooking, attention should be made that the protein network does not coagulate sufficiently strongly to squeeze water out of its structure.

Therefore grilling is usually used for thin and tender cuts like chops and steaks, because the inner temperatures will increase more quickly, so the inner parts of the meat will be cooked before the protein network in the outer surface starts to undergo syneresis that squeezes out internal water.

One of the most effective ways to avoid drying out of the centre is to cook the meat at these high temperatures as briefly as possible on each side, to initiate the Maillard reactions and kill any harmful bacteria, and then reduce the pan temperature by reducing the heat, or even totally removing the meat from the pan and letting the inner parts cook more slowly as the heat penetrates through. Since the inside is therefore subjected to lower temperatures, it is less likely to dry out, and there is no risk of the surface burning because it is no longer in direct contact with the heat.

Preparing meatIf the meat is salted before it is grilled, the juices will start to leave the meat by the process of osmosis, decreasing overall juiciness and tenderness. Equally, these juices that have left will surround the meat, and prevent browning reactions until all the liquid has evaporated.

Juiciness is also reduced by pricking the meat with a fork before grilling. This creates channels which increase the amount of juices that leak out during subsequent grilling.

Adding pepper is not recommended because the pepper will be cooked and burnt, which is not a desirable taste.

Presence of the boneMeat grilled on the bone is usually much tastier. This is due to several factors. Deposits of fat are usually found next to the bone in chops. Thus removing the bone may remove some fat with it, which will remove some of the taste (since fat is a crucial source of flavour). Also, the meat will seem drier because the fat melting during cooking increases the perceived juiciness of the final product.

The bone also in some ways "protects" the meat next to it. Bone is a poor conductor of heat, so meat located right next to it will not cook so fast and will remain juicier.

Spit roasting:Spit roasting is a similar technique that is used for whole animals. As the animal is slowly turned, every part of the outer surface can reach the Maillard temperatures to ensure even browning and flavour production. Because the animal is constantly turned, the heat penetrates the animal much more slowly, compared to if the animal was kept in the same position, and the meat cooks much more gently and is less likely to dry out. Equally the constant turning helps the flavour producing proteins and sugars to evenly disperse themselves throughout the animal, improving flavour distribution.

Sautéing:Sautéing is similar to grilling except that a fat source (butter, oil or both) is first added to the pan. The presence of a fat source further improves the heat penetration and prevents the meat from sticking to the pan. Equally, the presence of the fats may improve the flavour compounds produced by interacting with the Maillard reactions.

Cooking in a gas

Roasting:Placing a joint of meat in a hot oven heats it up due to the movement of the hot air molecules. This is another form of transferring heat by convection, like boiling, and a much more even method of transferring heat to the whole outer surface. The outer surface will reach higher temperatures, and cook faster, while the heat from the outside is slowly transferred to the inside of the meat, cooking it more slowly.

At low temperatures:When meat is cooked at oven temperatures of approximately 100 °C, water evaporation from the meat surface is slow. This means temperatures are limited to 100 °C and Maillard reactions are slow. This means that there is little surface browning and cooking times are longer. The temperatures reached inside the meat will be fairly low (around 60 °C), reducing moisture loss (so the meat is less likely to dry out) and the meat cooks evenly. Leaving a joint to sit after roasting, allows a redistribution of juices from the inner parts, where they are most highly concentrated because this meat was heated to the lowest temperatures, to the exterior parts, so the meat will have a more even juice distribution. Equally, cooking at these low temperatures allow the meats own enzymes, which function very efficiently at these low temperatures, to continue to work to tenderise the meat.

It is difficult to overcook meat at these low temperatures because it will stay at the right "cookedness" for quite a long period of time.

Low temperature roasting is good for big cuts of meat, especially those containing large amounts of collagen, whose degradation is favoured with the long cooking time.

At high temperaturesCooking meat in ovens set at high temperatures allows immediate protein coagulation and water evaporation, which forms the crispy skin, substantial browning and flavour production will take place on the meats surface. Heat will be transferred more quickly to the centre of the piece of meat, which will reach a higher temperature during cooking and may risk drying out. The meat will cook more quickly but therefore be more likely to overcook.

Maillard reactions will be more pronounced in a traditional oven (which has dry air) compared to a steam oven (humid air), yet so will the rate with which the meat dries out.

The oven door should not be opened because the volatile aromatic molecules that are produced during roasting will be released, so more aromatic molecules will diffuse from the meat by diffusion. High temperature roasting is more suited to smaller cuts of meat, which will be cooked before they have enough time to dry out. The oven should preferably be pre-heated. The meat then takes less time to reach the required temperature, so cooking time is further reduced and more juice is preserved.

A compromise?The best compromise is to start the oven at a high temperature to encourage surface browning, and then to finish the cooking at a lower temperature to cook the meat more slowly and prevent undesired texture changes.

Steaming:Steaming is a very efficient and quick way of transferring heat – there is therefore a risk that the meat will dry out very rapidly. It is thus only really suitable for thin tender cuts of meat that will cook quickly at the centre before the outside has dried out too much. Thicker cuts to be steamed are often wrapped in leaves to protect the surface from cooking so quickly.

Pressure cooking:In pressure cookers, water boils at approximately 130 °C. This greatly increases heat transfer, and therefore cooking time, and allows the collagen-gelatine conversion to occur much more rapidly. Cooking times are much shorter, and this easily leads to over-cooking. Meat cooked in a pressure cooker will become very dry, due to very high temperatures, and only really fatty cuts should be used (the fat deposits slightly reduce the perceived dryness).

Cooking using radiations:

Microwave cooking:Cooking meat in a microwave imparts energy to the water molecules of food. As this molecular motion means heat, microwave cooking heats water in food; and the water of the food heats the other molecules of food.

As almost all the energy given to the oven is transferred to the food, this process is very fast... and results sometimes in a large fluid loss and very dry meat.

No Maillard reactions can occur noticeably, so the characteristic flavours and tastes are not generated. The meat should be browned before to get coloration.

SUMMARY:In summary, small tender pieces of meat should be cooked at a high temperature for a short time to maximise browning and flavour producing reactions and to reduce drying out. The risk of overcooking these meats however is fairly large.

Larger pieces of meat, or very tough pieces of meat should be cooked for much longer times at much lower temperatures, to ensure complete collagen breakdown without temperatures being sufficiently high to cause significant drying out of the meat. Such cuts of meat can be first heated to a very high temperature, to kill bacteria and promote Maillard, and then finished off at the low heat. The risk of overcooking these meats is much less.

What we make from culinary ingredients: Ice cream

Ice cream compositionIce cream is composed of three basic elements – 60 % of ice cream is water molecules, 15 % is sugar (both added and the natural sugar lactose that is present in milk and cream), and 15 % is fat (provided by the cream and milk).

Making ice cream

Traditional preparationIce cream is prepared by mixing the milk, cream and sugar in the appropriate ratios, and then freezing the mixture as rapidly as possible. Freezing will cause the water molecules to form crystals. Due to the high sugar content of ice cream, one fifth of the water remains unfrozen even after freezing to –18 °C (it is held too strongly by the sugar molecules). If ice cream did not contain any sugar, all the water molecules would crystallise, and the resulting ice cream would be composed of entirely just water crystals and solid globules of milk fat, which does not give a desired texture to the ice cream. The liquid that remains unfrozen contains all the sugar, milk fat and milk proteins, and this thick liquid coats the ice crystals, making them stick together better.

The importance of freezing quicklyFreezing the mixture quickly ensures that a large number of small crystals are formed. If the mixture is frozen more slowly, fewer larger crystals will form. Ice-cream containing large crystals is undesirable – it has an icy texture and appears to cut the tongue. Small crystals give ice cream its creamy and smooth texture.

The importance of stirringDuring freezing, the mixture is stirred. This has various advantages:a) Stirring incorporates air bubbles which helps disrupt the ice crystal network and makes the final ice cream lighter and easier to bite into.b) Stirring ensures that the mixture is cooled in an even fashion, by ensuring even contact of the mixture with the cool sides of the container in which the ice cream is frozen.c) Stirring also helps break down any large water crystals that form during freezing, ensuring that only small crystals form.

Stirring is usually stopped before the end, to allow any remaining water molecules to crystallise onto already existing crystals – the crystals need to be a certain size to hold the ice cream together.

Storing ice creamIce cream should always be stored in the freezer covered. The fat component of the ice cream will tend to absorb odours from other products in the freezer, and may also go rancid in contact with the freezer air, if the ice cream is left uncovered, which affects its flavour.

Serving ice-creamIce cream is ideally served at 6 °C – at this temperature, about half of the water contained will be in its liquid state. This gives it a desirable texture and makes it easy to eat.

Continuous cycles of freezing and defrosting:Ice-cream should not be refrozen and defrosted continuously. Each time the ice cream is defrosted, some ice crystals will turn back into water. As it is re-frozen, unless the mixture is stirred, the water present will join those crystals that have survived, forming fewer bigger crystals. This gives the ice-cream a less favourable texture.

New ways of making ice cream

The PacojetIce creams and sorbets are now increasingly being made with a Pacojet. This new culinary tool is a machine that has a small blade that turns at about 2000 rpm, and each turn shaves off a layer of the product, and the blade gradually descends. Only one mini cycle is needed to make a portion of ice cream, and this takes less than a minute.

The Pacojet works by simultaneously breaking down ice crystals to create a smooth texture, as well as incorporating air as the blade turns. To make an ice-cream with the Pacojet machine, sugar is not essential, which means that these machines are being used more and more to make savoury ice cream.

Liquid nitrogenLiquids can also be rapidly frozen in liquid nitrogen to make ice cream instantly. Nitrogen is a gas at room temperature, but it can be made to liquefy if it is highly compressed and kept at very low temperatures. When this liquid is released, it is very cold (–196 °C), and will freeze an ice cream mixture instantaneously, with an improved texture due to much smaller ice crystals.

The nitrogen will evaporate rapidly on freezing the ice cream so will leave no residual taste.

Safety advices: Because liquid nitrogen is so cold, much care must be taken when using it, including wearing gloves and safety goggles.

What we make from culinary ingredients: Gnocchi

CompositionGnocchi is another sort of dough that is composed of a mixture of flour and water, to which eggs and a large quantity of pre-cooked and pureed potatoes are added, which increase the dough's overall starch content.

PreparationThe dough formed is well kneaded to denature the flour proteins and allow them to form a network around the flour starch granules and the potato cells. Once the gluten network has sufficiently developed and the dough has become sufficiently strong, it is moulded into small balls and cooked in boiling water.

Cooking

MechanismDuring cooking, the flour starch granules will take up water and swell as they gelatinise, making the gnocchi increase in volume. Gnocchi do not increase in volume as much as dried pasta and rice on cooking, because much of its starch content is provided by the potato cells and the starch granules in these cells have already gelatinised. The gnocchi keep their shape because the egg proteins on the surface of the gnocchi, which are in direct contact with the boiling water, will be heated up very quickly and will coagulate rapidly, keeping the gnocchi together and preventing it from falling apart.

Why do they rise?When gnocchi are placed in cooking water they fall to the bottom, because they are composed mainly of starch, and starch is more dense than water (if flour is placed in water it will fall). As the flour starch starts to gelatinise, more and more water will enter the gnocchi, reducing its density more and more to that of pure water, however its density will always be greater than the density of the cooking water. So why do they float to the surface of the pan? Gnocchi float because tiny bubbles of evaporating water get trapped in the crevices in the gnocchi. When the crevices are filled with these tiny bubbles, they are pushed up to the surface. If a gnocchi that has risen to the surface of the cooking water is removed from the pan, and slowly rolled on a surface to remove the trapped air bubbles, when this gnocchi is put back in the cooking water, it will sink. (This is the same phenomenon as when cauliflower rises during cooking – cauliflower has a very irregular structure in which bubbles of water vapour are easily trapped – when the cauliflower floats, if it is removed and its surface tapped, they will fall when returned to the cooking liquid).

So when gnocchi rises to the surface of the cooking water, it does not necessarily indicate that the gnocchi is cooked, but more indicates that a sufficient amount of water vapour has been trapped in its crevices. This has nothing to do with how well the gnocchi is cooked. A gnocchi will be cooked when internal temperatures have been reached that allow significant levels of egg protein coagulation and flour starch gelatinisation. This occurs at around 70 °C.