An introduction to technological applications of Molecular Gastronomy. Part 1.

Before learning how to cook, we should know what cooking is really.

Of course, technique is important: we have to know how to break an egg, how to roast chickens, how to make mayonnaise sauce, etc. but technique alone does not make a dish. The same for piano playing: if you know how to put your fingers on the keys but if you don't know which song to play, there is no song. Hence, art is first, and technique second.

Is cooking art and technique? No, because well swollen soufflés, with all the fine ingredients in them, thrown at the face of the guests are not "good"; the dish is prepared for someone very particular, and some "love" has to be given. "Love"? The term seems unscientific, but everybody understands what it means: a simple sandwich shared with very good friends can be a delicious meal, but a very well prepared meal shared with enemies is not good. This demonstrates that we eat "love": love given by the cook, and love shared with the other guests. Hence the new question: how to give love, in creating dishes or in organizing meals to be shared between many guests?

Coming back to learning, culinary technique should be learnt in the perspective of giving love, and culinary art should be learnt according to the same idea.

Technique learning

Let's consider technique first. As for other crafts, cooking is applying processes in order to control phenomena. For example, mayonnaise is produced by dispersing oil in the water of egg yolks and vinegar. The oil has to be poured slowly, the whisk has to be moved with enough energy so that dispersion occurs. During the process of mayonnaise making, a lot of physical and chemical phenomena occur: oil is divided into tiny droplets that are covered by some particular molecules from the yolk (proteins, lecithins…), energy is consumed in this oil droplets division and probably also transformed into heat, etc.

Hence a conclusion: in order to learn efficiently how to cook, it is useful to understand the result of the actions (phenomena) and also to study the relationship between what the cook does and the physical and chemical phenomena resulting from what he or she does: "the head should drive the hands".

Chemistry in the kitchen? Physics in the kitchen? This is not new, as even Marie-Antoine Carême, the most famous of all French cooks, wrote on the first page of the first volume of his treatise L'art de la cuisine française, in 1847:

"In the houses of craftsmen, stock is the most nutritive food, in spite of what wrote the Journal Le Gastronome. Women care about the pot, without knowing any chemistry; they only learnt from their mother how to do it. First they put meat in an earth pot, adding the necessary water (two litres of water for three pounds of beef meat); then they put the pot at the corner of the fire and, without knowing it, they make a chemical process. The pot heats slowly, heat of water increasing gradually, and dilating the muscular fibres of beef, so that it dissolves the gelatinous matter that is between them. By this way, with slow heat, scum is floating up slowly; osmazome, which is the tastiest part of meat, dissolving slowly, gives some unction to the liquid, and albumin, which is the scum producing part of muscles, dilates easily, goes up forming light scum. Thus, by the simple process of slow heating, the women obtain a nutritious and tasty stock, as well as a good and tender boiled meat."

Carême was not the first to speak of chemistry in cooking, as Marin also wrote in La suite des dons de Comus: "Cook's science is to dissociate, digest and quintessence meat, to draw from them nutritious and light juices. This kind of chemical analysis is indeed the main part of our art".

These two quotations recognize fairly that there is some relationship between cooking, on one hand, and chemistry and physics on the other hand. However they are wrong, strictly speaking. Indeed, it is not true that cooking is science, because a craft is not a science (i.e. the exploration of the mechanisms of phenomena). Cooks have to produce food, but scientists have to produce knowledge. In particular, chemistry is not grilling steaks, but trying to understand what goes on when steaks are grilled. And it is not true either that cooking is chemical analysis: chemical analysis tries to understand the chemical composition of food, it does not cook food. Making and studying are different jobs.

More generally, craft, technology and science are different activities, with different objectives. However, scientific knowledge is useful, because it remains true that the phenomena involved in the kitchen (browning of the steak during cooking, thickening of the mayonnaise sauce during making, etc.) are chemical and physical transformations. As science is invited in the culinary curriculum, let's first look for the main phenomena that have to be considered. Ten only should probably be taught in all culinary schools:

What we make from culinary ingredients: Bread and other flour water mixtures

General overview

Many dishes prepared in the kitchen are made of a basic mixture of flour and water, known in cookery as dough. Often in cooking this basic dough is mixed with other ingredients such as a raising agents, eggs, sugar, and milk to make a large range of diverse products. These include breads, cakes, pastas and quiches. Each of these products has a different ratio of flour and water, and is mixed with one or several other agents to give all these products their associated textures on cooking.

Product	% water	% flour	Other products
Bread	35	55	Salt, yeast
Cakes	20	25	Butter, eggs, sugar
Pasta	20	75	Eggs
Pastry	15	50	Butter

When the dough is cooked, the starch granules in the flour will swell, the flour proteins will coagulate, and the resulting dough will gradually become hard as the amount of free water is reduced. Details for the preparation and cooking process are given below for making bread; the other introduced types of dough are discussed in the following sections.

Bread is made from mixing flour, water, yeast and a little salt. Yeast is a living organism, made up of only a single cell, which lies "asleep" until it comes into contact with warm water. Once "woken up" with heat and water, the yeast begins to feed on any sugar it can find, releasing CO₂. As it feeds on the sugar, it is provided with energy which allows it to grow. Yeast grows by dividing its cell membrane and all its cell contents evenly in two to form two new cells.

Kneading

When preparing bread, the flour is mixed with the water, salt and yeast to form a dough. The first process of making bread involves kneading this dough until it becomes smooth and stretchy, due to the gluten proteins present in the flour.

The gluten proteins:This initial kneading step helps unwind the gliadin and glutenin proteins by breaking their hydrogen bonds and disulphide bridges, which then line up to form and develop the strong gluten network. Some intramolecular loops that are preserved in the proteins give the dough its elasticity. The strong and elastic dough produced is able both to trap the air bubbles without breaking due to its strength and to allow the bubbles to expand during cooking due to their elasticity. The addition of salt helps the protein network by using its charged ions to favour the attraction of the proteins to each other and therefore the formation of a protein-protein network.

The other proteins:As well as the gluten forming proteins – flour also contains other proteins that play an important role during the kneading step. These include the enzymes, and most specifically the amylases have a particularly important role in bread making. These enzymes use the water present in the dough to attack both the amylose and amylopectin molecules located in the starch granules in the flour at random points in their structure to break them up into molecules of maltose (a simple sugar molecule made of two glucose molecules chemically joined together). These molecules will later be used by the yeast to respire, during a process called fermentation. It is for this reason that flour should always be kept dry, or the enzymes will start to react with the starch in the flour during storage using water vapour from the air, degrading the starch. The amylases work fastest at warmer temperatures, which is why warm water is usually added to the original dough rather than cold.

Salt:The addition of salt promotes the activity of the flour enzymes, the amylases, but decreases activity of the proteases present in flour – which would otherwise hydrolyse the flour proteins and produce a weak dough.

Fermentation

After adequate kneading, the dough is placed in a bowl, which is covered and left for several hours (this is called fermentation). This allows the dough to swell as the yeast respires, producing the gas CO₂. The bubbles do not escape but remain stably incorporated in the dough. The air bubbles are trapped in the strong protein network.

The yeast is not only responsible for the production of gas bubbles during this time, but also the flavours and smells that accompany yeast respiration.

During the fermentation, the yeasts use their own enzymes, the maltases, to degrade the maltose produced by the flours amylases into glucose molecules. It is these glucose molecules directly that are then converted into carbon dioxide (which helps the bread rise), ethanol (which gives bread its taste), and diverse aldehydes, ketones, diacetyl, and other alcohols (which help contribute to the breads flavour).

C6H12O6⟶2CO2(g)+2C2H5OHC6​H12​O6​⟶2CO2​(g)+2C2​H5​OH

This is also how the alcohol in beer and other alcoholic drinks is produced.

Fermentation is most effective at temperatures of 27 °C. Although higher temperatures will make the yeast grow faster and produce more gas, which would increase dough volume, the flavour produced is best at this lower temperature.

Second kneading step

After fermentation, there is a second kneading step. This step is not so much to strengthen the gluten, but the constant folding over of the dough during kneading allows the incorporation of air into the mixture, and ensures that it is distributed evenly.

This second kneading step also helps distribute the yeast cells evenly throughout the dough. After this second kneading step, the dough is again left to rest to allow further yeast respiration. Because the yeast cells have been distributed evenly, the CO₂ produced will be distributed more evenly throughout the dough.

This complex preparation step of kneading and fermenting thus produces a light and airy dough where the even distribution of gases produces a more evenly risen final product after baking.

Cooking

Initial cooking

Once the dough has risen sufficiently, it is placed in a hot oven.

During the initial stages of baking (i.e. the first 10 minutes), the dough will expand greatly in volume – this is known as "oven spring". This is due to a number of contributing factors:

• As dough temperature increases up to about 60 °C, both amylase activity as well as yeast activity increase. Increased amylase activity results in the more rapid conversion of starch to maltose, which further increases the yeasts food supply. Increased yeast activity means that more CO₂ will be produced, further increasing the quantity of gas incorporated in the dough. When temperatures greater than 60 °C are reached, the enzymes are deactivated and yeast cells die. The yeast stops producing CO₂.

• As temperature increases, all the gases – i.e. the CO₂ produced by the yeast as well as the air introduced during kneading – expand.

• Also, some of the free water in the dough, as well as the ethanol produced by the yeast, will evaporate, further expanding the dough.

So the first ten minutes of baking are associated with a high level of gas production and expansion. Due to the relatively elastic nature of the protein network in the dough, these gases will expand without breaking the protein network. However, before cooking, several cuts are normally made on the top surface of the dough with a knife, to further increase the ability of the dough to expand, so that it can expand further as the gases expand, without forming unattractive cracks.

High temperatures strengthen the network that has formed between the proteins during kneading, and the network becomes more and more rigid. Simultaneously, the starch in the starch granules gelatinises, taking up water, and this effect, combined with the level of water evaporation, causes the dough to start to harden.

Further cooking

Crust formation:Temperatures at the breads surface increase faster than inside the bread. This forms a dry and hard crust, which prevents any gases from escaping, maximising swelling of the dough. Therefore bread is often cooked in a very hot oven to initiate the solidification of the crust, which reduces subsequent gas escape and a decrease in bread volume. Dishes such as quiches are also cooked at a high temperature to ensure this impermeable crust on the surface to prevent significant amounts of water vapour from escaping. This is so that sufficient water vapour is still there at the end of cooking to condense, and ensure that the quiche remains tender on cooling.

Texture changes:As the gases, which are unable to escape, continue to expand, the pressure inside the dough increases. This increase in pressure causes some of the protein network to be broken, which allows the gas bubbles to interconnect with each other.

Flavour production:As temperatures at the surface exceed 100 °C, Maillard reactions begin to occur between the reducing sugars and the amines in the crust, producing the noticeable colour and taste of bread. In the presence of milk, these Maillard reactions are even more favourable. Milk contains the sugar lactose, which, unlike maltose, can not be broken down and used as a food source by the yeast, so its inclusion in the original dough provides an increased total sugar concentration available for Maillard reactions, improving the breads brown colour and the taste.

Overcooking:Cooking bread at too high a temperature may cause the protein network to become too rigid, due to strengthening of the network, before the gases have had time to fully expand. When the gases start to expand, they are unable to stretch the protein network (which is too rigid), and the bread remains fairly flat. Equally, under kneaded dough will produce bread with a reduced volume, because less air will be incorporated, so there will be less overall gas expansion during cooking and the bread will remain fairly flat. This dough will rise less during subsequent cooking, even at an ideal temperature.

If, however, the temperature is too low, the gases will swell before the bread has formed its hard outer crust, so the gases will expand and the bread will stay flatter.

After cooking

On cooling, starch that has been released from the starch granules will start to bond to each other, trapping the water present into a gel. This makes the soft centre of the bread become harder, which actually makes it easier to slice the bread. After a few days, starch bonding is so great that water is squeezed out of the network and the bread becomes so hard it is no longer edible. Therefore, stale bread can be softened slightly by heating it, because it allows the starch molecules to become mobile again, releasing trapped water, and softening the dough.

What we make from culinary ingredients: Cakes

Cake composition

Cakes are another sort of dough, in which the flour is mixed with eggs, sugar and butter. This mixture is then cooked to produce a light and fluffy cake, filled with gas. The gas bubbles contained in the cake are not produced by yeast, like in bread, but rather are incorporated into the cake mixture either by using chemical gas producers (like baking powder), or mechanically by beating in air.

The different ways of introducing gas

Chemical methods:Chemical leaveners (e.g. baking powder and soda) are compounds that give off carbon dioxide when placed in hot water. Their primary component is the alkali sodium bicarbonate, which is either mixed with acid already (as in baking powder) or needs the addition of acid to function (as in baking soda). In the presence of water, one of the two acids contained in baking powder will react with the sodium bicarbonate present to produce bubbles of CO₂. (Baking powder thus often contains starch, which acts to prevent early reactions between the bicarbonate and acid molecules, by absorbing moisture and helping keep the powder dry). The second acid present in baking powder reacts with sodium bicarbonate at higher temperatures, to produce more bubbles of CO₂ during the beginning of the baking process. When using baking soda, the sodium bicarbonate will react with acid present in the cake mixture to produce CO₂. Baking powder and baking soda are more efficient raising agents than yeast, and produce CO₂ much faster, however they do not improve the taste and flavour of the dough in the way that inclusion of yeast does.

Mechanical methods:Gas can be incorporated into a cake mixture mechanically by a process called creaming. Creaming involves incorporating air bubbles into the butter by beating the butter with an electric mixer. Then sugar (granulated, not powdered) is sprinkled slowly into the butter. As the sharp sugar crystals cut into the butter structure, tiny pockets are formed between the butter crystals. These pockets fill with air, and as the mixer blades pull more butter over the top, these pockets get sealed in place. Alternatively, air bubbles can be introduced by incorporating a previously aerated mixture, such as whipped cream or whipped eggs, which is carefully introduced into the mixture. Cake mixtures should not be over-mixed during the preparation, as this will cause them to lose CO₂ or the air incorporated by creaming.

Cooking

As the cake is cooked, the CO₂ or the air incorporated during mixing will expand, and the water contained in the mixture will evaporate, and this will cause the dough to rise. These bubbles are held in the mixture by the network that forms around the bubbles as the denatured flour proteins coagulate, and surrounds and holds the air bubbles in place. The supporting network is not as strong as it is in bread, where the flour used has a high protein content and the dough is well kneaded to strengthen the gluten network before cooking. The flour used to make cakes is usually low in proteins, to actually reduce the amount of gluten formed and thus prevent a very tough texture. During cooking, the starch granules provided by the flour will start to take up water and swell, increasing the viscosity of the cake mixture. A thick cake mixture will more stably incorporate introduced bubbles than a liquid mixture. As temperatures increase further, significant evaporation of water from the upper surface of the cake will make the cake hard, and will allow the taste and colour producing Maillard reactions to occur.

Normally, the faster a cake is heated (i.e. the higher the oven temperature), the more the gas cells have a chance to expand before the cake sets, so the result is much more light and tender.

Cooling

When the cake is removed from the oven, it cools – the gas bubbles contract and the vapour condenses. These two effects reduce the internal pressure, and often cause the cake to fall in on itself if its supporting protein network is not yet sufficiently strong (i.e. if the cake was undercooked).

Staling

A cake will stale more slowly than bread – this is because the water that may otherwise be lost as the protein network strengthens and starts to squeeze out water is kept in the structure by the presence of the sugar molecules, to which it bonds.

What should be known about culinary ingredients: Simple carbohydrates – simple sugars

Food contains three major groups of molecules: sugars, proteins, and fats. The sugars are compounds containing carbon, hydrogen and oxygen atoms. Many of them were called carbohydrates because these atoms are bonded together in the ratio: Cₓ(H₂O)ᵧ. Sugars include carbohydrates, but also starches, cellulose and many other compounds found in living organisms.

Structure

If a sugar contains many joined units, they are called polysaccharides; otherwise they are monosaccharides. The most common monosaccharides encountered in the kitchen are glucose, fructose and galactose; but there are many others. Glucose, fructose and galactose all have the same chemical formula (C₆H₁₂O₆) but the arrangement of atoms differs in each case.

Glucose and fructose are found in many fruits and in honey, in a mixture with other sugars, whereas galactose, in contrast, is found more commonly in non-fermented dairy products.

Sweet fruits and vegetables such as carrots and beetroot contain large amounts of these sugars. Fructose is the sweetest of all the sugars, but its sweetness is reduced by about half on heating to 60 °C. Glucose is less sweet than fructose.

However, these sugars are not found in this simple unjoined form in the kitchen very often. More often the single sugar units are joined together to form larger sugar molecules. If a carbohydrate contains two of these sugar units chemically bonded together it is called a disaccharide. When two monosaccharides combine to form a disaccharide, an OH group from one of the sugar units is used to form a link with another. This link is called a glycosidic bond. The most common disaccharides found in the kitchen include:

a) sucrose – this is composed of one glucose unit joined to one fructose unit – this sugar is what we know as table sugar. It is the second sweetest sugar (after fructose), and is usually used to make candy because it has a pleasant taste even at high concentrations and interesting texture properties. (Some of the other sugars have a slightly bitter taste at very high concentrations).b) lactose – this is composed of one glucose unit joined to one galactose unit. It is rarely found in the kitchen in its pure form and is the sugar naturally found in milk. It is much less sweet than sucrose, so is not really used as a sweetener.c) maltose – this is composed of two glucose units attached together, and is the sugar naturally present in barley.

Digestibility

The monosaccharides and disaccharides together make up the group of carbohydrates known as the "simple sugars". They are called "simple" because they are readily broken down and absorbed by the body, due to their simple structure, and therefore give an immediate energy supply.

During digestion, these sugar molecules are broken down by the body's digestive enzymes. Some people do not produce the enzyme lactase that is responsible for digesting lactose, commonly found in milk. These people suffer from the disease lactose intolerance. They cannot digest lactose, or dairy products containing lactose.

Solubility in water

Simple sugars have many groups composed of one hydrogen atom linked to one oxygen atom, this oxygen atom being attached to the molecule. These -OH groups make sugars soluble in water, because they can interact with water molecules. In the absence of water, these groups will be slightly attracted to each other and will cause the sugar particles to line up in a regular pattern. This structure is called a crystal structure. It is because they form these crystals that we are able to see sugars. A single disaccharide is far too small to see with the naked eye, but when millions of disaccharides join up to form a crystal the sugar is visible. These crystals can greatly vary in size – for example in caster sugar, the crystals are fairly large and obvious, but in icing sugar, the crystals are much smaller.

The presence of these OH groups also makes the simple sugars readily soluble in water. In the presence of water, their OH groups will preferentially bind to water molecules than to each other, because these OH groups are more strongly attracted to the water molecules, so the sugar crystal will break up and the sugar units will evenly place themselves throughout the water. The sugar is said to have "dissolved". The solution will thicken as the presence of the sugar molecules reduces the ability of the water molecules to move around each other freely.

Fructose is the most soluble of the simple sugars (it can dissolve in one quarter of its volume of water), whereas glucose is slightly less soluble and therefore produces a less thick solution when dissolved in water. Sucrose is also surprisingly soluble in water – it is actually the second most soluble sugar in water and can dissolve in half its volume of water to produce a thick solution.

After a certain point, no more sugar can dissolve in a sugar solution because there will be no more water molecules available to bond with the added sugar – the sugar will stay in crystal form and will not dissolve. We say that the sugar solution is saturated.

Effect of heat

Standard heating

Unlike the carbohydrates, proteins and fats, the sugars are small and stable molecules that are remarkably resistant to heat. A mixture of a sugar and water can be heated to boiling temperatures without affecting the sugar structure. As the mixture is boiled, water molecules evaporate from the mixture, and gradually the solution will become more and more concentrated in sugar, the sugar molecules will start to bond with themselves to form pure masses or solid crystals. This is how sweets are made.

The boiling temperature of a sugar solution will always be higher than 100 °C. This is because heat is needed to not only break the water-water linkages but also to break the strong sugar-water linkages. So the solution will need to be heated to a slightly higher temperature before the water can become a gas.

Also, the more concentrated the solution is in sugar, the higher the boiling point. Therefore, as the solution is heated, more and more water evaporates, so the solution becomes more and more concentrated in sugar, further increasing in boiling point. A sugar solution with a sugar concentration of 90% will boil at about 125 °C.

Extreme heat – caramelisation

If simple sugars are heated to a sufficiently high temperature (which will happen when all the water has evaporated from a sugar solution), it will eventually start to develop a characteristic "caramel" taste as the sugar molecules themselves start to break down. The monosaccharides are fairly reactive, and when heated to high enough temperatures, atoms within the monosaccharide molecule will start to break away in a fairly violent manner, and the remaining structures will reorganise into new molecules, which themselves may recombine to form new molecules.

These new molecules that are formed are responsible for generating both a large range of flavours and a brown colour, and the process is known as caramelisation. The more the caramel is heated, the browner it will become, and the less sweet it will taste (as the molecules responsible for the sweet taste are gradually broken down). A caramel should be removed as soon as it has developed a desirable brown colour – over cooking a caramel will make it very dark, bitter and extremely thick. Disaccharides are less reactive than monosaccharides (since their reactive group has been used in forming the sugar dimer). Therefore, disaccharides like sucrose caramelise at a higher temperature than the simple sugars because the disaccharide must be first broken down into its component monosaccharides, which are sufficiently reactive to undergo these characteristic reactions which produce the caramels taste and colour, and this requires further heating. Sucrose will caramelise at 170 °C, whereas glucose will caramelise at 150 °C. (Fructose caramelises at the much lower temperature of 105 °C, just above the boiling point of water).

Making a caramel: In the kitchen caramels are most often made with sucrose. When a solution of sucrose and water is heated, some of the sucrose molecules will acquire enough heat to break down into its component glucose and fructose monomers. These monomers may lose some atoms and rearrange to form new molecules, or else may recombine with other molecules to produce different structures, for example the fructose monomers produced may themselves recombine to form fructose dimers, and these new dimers produced by the heat may then react further with glucose, or even again with fructose. Some of these molecules may also break down into smaller and smaller parts. The large number of different molecules produced are responsible for the characteristic smells and taste of the common caramel. When caramels are prepared in the presence of ingredients containing proteins or amino acids (like cream or milk), in addition to caramelisation, the sugars will react with amino acids from the proteins to produce an even greater variety of flavours and colours.

However, table sugar is often replaced by sugar substitutes, like aspartame. When this molecule is heated, some of the aspartame molecules break down into an aspartic acid sugar unit and a phenylalanine unit. These two sugars are not associated with this appreciated "caramel-taste" and furthermore, aspartic acid has a slightly bitter taste.

Effect of acid

When a disaccharide such as sucrose is heated in the presence of acid, it will break down into its component sugars. This is because the glycosidic bond that joins the two sugar units together is broken down. Breaking a disaccharide up in this way is known as inversion, and has uses in the kitchen, especially in making sweets because it reduces the amount of crystallisation.

Monosaccharides, by contrast, are little affected by pH because all the bonds in their structure are very strong covalent bonds, which are not readily broken down in acid, and require very high temperatures before they will start to break down.

Reactivity with proteins

Simple sugar molecules are also able to react with the subunits of proteins (called amino acids). When an amino acid and a simple sugar meet, there is a rearrangement of atoms, and some atoms are released (usually two hydrogen atoms and an oxygen atom, which forms a water molecule). New molecules are formed from what remains. This simple reaction can produce many different new molecules depending on which rearrangement has occurred. Furthermore, these newly formed molecules can either break down to form other new compounds, or react further with each other to produce other new molecules, or even react with other molecules if they are present (such as the fats) in various ways to produce even more molecules.

It is the large combination of all these different molecules that gives cooked food its colour, taste and smell. The final taste perceived on eating a piece of food depends on the profile of all these different molecules produced, and their concentrations. For example, the taste of roast beef contains over 600 of these sorts of molecules.

All these reactions are collectively known as the Maillard reaction. The Maillard reaction occurs most rapidly at temperatures of around 150–250 °C, but if there is a high concentration of sugars and amino acids, then it will occur at lower temperatures. The reaction is thus favoured in dry conditions, and will only really start to occur in cooking when all the water from a food source has evaporated, and temperatures can therefore exceed 100 °C.

Maillard reactions are also affected by pH – in an acidic environment, a totally different combination of molecules are formed to when in an alkaline environment, so the resulting taste will be totally different.

Role in cooking

In cooking, simple sugars have two main roles – firstly they are responsible for the sweet tastes of some foods, and can be used to sweeten other dishes. As well as being used to attribute sweetness directly to a dish, sugar can be added to reduce the perceived bitterness or sourness of a dish, and it has also been shown to enhance our perception of other flavours.

Secondly, since they are major players in the Maillard reactions, they are also generally responsible for the generation of flavour and taste produced by cooking.

What should be known about culinary ingredients: Proteins

What are proteins?

Like other major food groups, proteins are big molecules composed of smaller repeated subunits called amino acid residues. However, unlike the other food group subunits, the protein subunits contain the atom nitrogen as well as the atoms carbon, hydrogen and oxygen. The basic structure of an amino acid is shown below:

text

   R
   |
H₂N—C—COOH
   |
   H

Amino group (H₂N—) Carboxyl group (—COOH)

C = carbon atomH = hydrogen atomO = oxygen atomN = nitrogen atomR = refers to the part of the amino acid that varies between the different amino acids.

There are twenty different amino acids that are commonly found in proteins. Proteins consist of long chains of these amino acids, which are held together by strong bonds, called peptide bonds, like beads on a necklace (in this analogy the beads represent the amino acids, and the string represents the bonds). Because there are so many different amino acids, each of which may be joined to any of the other amino acids, there is a very large number of different proteins that can exist, and each one has slightly different properties depending on its amino acid composition.

Depending on whether the "R" group of an amino acid is charged depends on whether the amino acid is charged, or "hydrophilic", or whether it is non-charged, or "hydrophobic". An example of a hydrophobic and a hydrophilic amino acid is shown below:

Arginine has a polar/charged head, so is hydrophilic.Leucine does not contain any charged groups, so is hydrophobic.

Proteins are mainly found in the kitchen in meat and fish products, as well as eggs; and to a smaller extent in various vegetable seeds.

Protein structure

In food sources, proteins are usually found in the presence of water. Their native form is not in the form of these long straight chains, but rather in the form of highly folded chains (almost like balls of string) that form a 3-dimensional structure that is unique to each protein, and depends on its amino acid sequence. The chain is folded in such a way that all the amino acids that are "hydrophobic" are protected inside the protein, while those that like to be in contact with water are kept on the surface, where they are in contact with the water. The protein is held in this form by a number of forces between their side chains – these include bonds formed between sulphur groups (these are called sulphur bridges, and are among the strongest of all the forces), positive and negative parts of a protein (strong electrostatic forces), and between hydrophobic groups (slightly weaker hydrophobic interactions).

Some forces are also involved in stabilising intramolecular loops.

The hydrophilic groups on the outside of these proteins, because they are charged, help individual protein bundles to stay separate from each other. Raw protein sources are thus often transparent because the gaps between individual protein bundles allows light to pass through. This gives raw egg whites and meat and fish flesh their transparency.

In their highly folded form, proteins trap a considerable amount of water molecules within their highly folded structures. As these proteins start to denature, some water is actually freed from between the proteins and this causes an initial increase in "free water", which in food tends to be perceived as juiciness.

Protein modifications

Denaturation

The weak bonds that hold the protein 3-dimensional structure together can be fairly easily broken – by the addition of heat, acid, salt or mechanical force (e.g. mixing). As these bonds holding the proteins structure together break, the protein unfolds into its long chain, exposing all its previously protected amino acids. This process is called denaturation. Our stomachs more easily digest denatured proteins, so proteins are often expressly denatured (either by cooking with heat, curing with salt, or pickling with acid) before they are consumed. Heat is quicker to denature proteins than acid, salt or mechanical force, which is why cooking meat is a much quicker process than curing or marinating meat.

Uses of denaturation:

Denatured proteins have many useful functions in cooking. Not only are denatured proteins much more digestible than raw proteins (the groups are more accessible to digestion by enzymes), they are also useful in food preparations. Their use in such food preparations tends to be based on the principle that in denatured proteins, unlike in raw proteins, both the hydrophobic and the hydrophilic amino acids are exposed, giving the unwound chain both positive, negative, and neutral parts.

Eggs are the simplest source of proteins to use in these preparations, because they contain just protein and water. Meat and fish and vegetable sources however contain proteins in combination with a large number of other different molecules (starches, fats etc.) so they are used less often for the following functions of denatured proteins:

As emulsifiers:As previously mentioned, a mixture of fat and water will not be stable unless molecules called "tensioactive" molecules are present. These molecules contain a hydrophobic part and a hydrophilic part (or in simpler terms they have one end that is soluble in water, and one end that is soluble in oil). When present in a fat-water mix they tend to surround the fat droplets and insert their hydrophobic parts into them, leaving their hydrophilic parts to contact the water.

Proteins in their natural state only expose their hydrophilic groups, so cannot function as tensioactive molecules. However, as explained above, denatured proteins expose both their hydrophobic and hydrophilic parts, so can then function as tensioactive molecules to stabilise water-fat mixes.

For example, a mixture of vinegar, which is mainly water, and oil, can produce a very stable mixture when egg proteins are present (e.g. in a mayonnaise). The action of whisking will denature the egg proteins, which are then readily available to stabilise the oil droplets in the mixture.

As foaming agents:Air can be introduced into liquids by beating them with a whisk. Not all air-liquid mixes are stable. For example, when pure water is whisked, the air bubbles introduced are not stable – they rapidly rise to the surface, being less dense than water, and subsequently escape.

However when a liquid containing proteins (such as egg whites) is whisked, the air can be stably incorporated. Even though the air bubbles are much less dense than the liquid, they will not escape. This is because as the egg whites are whisked, the proteins contained are disrupted, and will start to denature, exposing their hydrophobic and hydrophilic parts. The proteins can then place themselves at the air-water interface, because their hydrophilic parts stay in contact with the water, while their hydrophobic parts, which do not like to contact water, tend to place themselves in contact with the air.

As thickeners:Blood is full of many proteins, and both blood and egg yolks can be used as thickening agents. Gentle heating will denature the proteins, and they will unroll into their long strands. These strands can then prevent the water molecules present from easily flowing around each other, in a similar way to starch molecules, and the liquid will thicken.

Proteins denature at various different temperatures – thus knowledge and understanding of the denaturation temperatures of various different proteins (i.e. egg proteins, meat proteins) can be very useful in cooking.

Coagulation

If the mixture is heated further after denaturation, the added heat will cause the denatured proteins to move around much more quickly. These unfolded protein chains will be attracted to each other if they contact each other, and will form bonds between their chains at particular hydrophobic or hydrophilic regions where they are attracted to each other.

As protein strands join together, a protein network is formed. This is known as coagulation. This process is also responsible for the loss of transparency of raw meat, fish and eggs on heating them – the network formed will not let the light pass through the strands as easily as when the protein bundles were separated, so transparency is reduced.

This network will trap the water molecules that were originally located between the unravelled protein strands, reducing the fluidity of the mixture, and eventually forming what is known as a "gel".

Uses of coagulation:

Coagulation can be both useful or a real nuisance in the kitchen. A custard becomes lumpy because the egg proteins have been heated to too high a temperature and the denatured proteins have begun to coagulate. However, gnocchi, pasta and other wheat-flour based products only keep their shape thanks to a coagulated protein network.

Thus understanding coagulation, coagulation temperatures of the different proteins, and factors that affect coagulation, can be very useful in the kitchen.

Factors favouring coagulation:

An unwound protein will contain areas along its chain that are charged, and these tend to prevent coagulation. This is because areas that are similarly charged (for example negatively charged areas on two neighbouring denatured protein strands) will tend to repel each other, reducing the chance of subsequent inter-chain bonding and thus network formation. This repulsion can be prevented by adding molecules to the protein mixture that are small and charged (such as the H⁺ in acid and Na⁺ and Cl⁻ ions in salt). These molecules will be attracted to protein regions of opposite charge to themselves, and help them "locate", and eventually bond to, areas on other protein strands from which previously they would be repelled.

The H⁺ ions also have an additional property that favours coagulation – as mentioned above, the presence of acid increases the rate at which proteins denature, which will further increase the rate of coagulation.

Factors disfavouring coagulation:

This can be achieved by adding substances that reduce the movement of the denatured proteins, making their subsequent coagulation difficult. In cooking, these molecules tend to be long uncharged molecules (like, for example, starch molecules).

Syneresis

As more and more bonds are formed between different unwound chains (including the electrostatic forces between positive and negative parts; the hydrophobic interactions between different hydrophobic parts; and the sulphur bridges between sulphur atoms), the network will become stronger and tighter, until eventually it will start to push out the water. This is called syneresis.

The process of syneresis is always undesired in cooking, since it is unattractive and results in foods drying out.

Role in cooking

So in conclusion, the roles of proteins in food and cooking are large and extremely diverse:

• Stabilising (both water-fat mixes and water-air mixes)

• Affecting texture – both water retention (gelling) and water removal (syneresis)

• Affecting taste by its role in the Maillard reactions

The large range of functions provided by this group is due to the large number of different proteins that can exist. The starches, for example, are based on a single subunit – the glucose unit, so the number of possible different structures that can be formed is fairly limited. As a result, the different starches tend to have similar roles.

The proteins however, can be composed of any combination of the basic twenty different amino acids, and this gives rise to an enormous number of different possible amino acid sequence combinations that can exist. Since amino acid sequence affects protein structure, an enormous number of different structures of proteins can exist. Since the structure of a molecule affects its functions, it is of little surprise that the protein group offers the chef such a wide range of different functions.

Some special proteins

Enzymes

Enzymes are a special group of proteins that control chemical reactions. The majority of reactions that control the living world do not occur spontaneously. In order for the substrates involved to react and produce their related products, an enzyme is needed to speed up the reaction. The enzymes themselves remain unchanged, but their presence is essential to allow changes in the reacting molecules. Enzymes contain an active site, into which the reacting molecules can fit. This brings the substances into close contact, favouring their reaction.

Enzymes are responsible for controlling both useful and undesired reactions in food and cooking. Although enzymes are responsible for controlling reactions producing undesirable effects such as the rancidity of foods and the browning of cut fruit and vegetables, they are also indispensable to cooking processes such as the making of bread and beer.

Enzymes are proteins, so their structure is thus affected by heat and pH. Since their structure, especially of their active sites, is essential to their functioning, understanding how pH and heat affect enzyme controlled reactions can be very useful to the chef – both in order to prevent the unwanted reactions, and increase the rate of those desired ones.

Pigments

Pigments are proteins involved in determining colour. Pigments will reflect only certain wavelengths of visible light, and will absorb all other wavelengths. This affects the final colour. For example, chlorophyll, the pigment found in green vegetables, absorbs all wavelengths of visible light except green, which it reflects. This is why green vegetables appear green. Red meat pigments absorb all wavelengths except for red, giving meat its red appearance.

The light absorbing properties of these pigments depends strongly on their structure. Even a very small change in structure may completely affect the light wavelengths that can be absorbed and those that are reflected. Since enzymes are proteins, and thus affected by changes in heat and pH, the colour of many foods will change when subjected to these extreme conditions. Understanding these changes can therefore be very useful in controlling the colour of vegetables and fruits, or even meat, in the presence of pH or heat.

What should be known about culinary ingredients: Fats

Fat structure

Fats are various molecules. One particularly important kind of fats are "triglycerides". Triglycerides contain a molecule of glycerol attached to three fatty acid molecules, as depicted below:

text

      O
      ||
H—C—O—C—R1
      O
      ||
H—C—O—C—R2
      O
      ||
H—C—O—C—R3
      |
      H

Glycerol Fatty acids

The R groups represent long chains of carbon atoms attached together, and the three R groups can either be different or all the same. Any of a large number of R groups can be attached to any of the three glycerol carbon atoms, so there is an amazingly large number of possible triglycerides.

The carbon atoms in the R chains can be attached to each other either with double bonds (C=C), or with single bonds (C–C). This will determine whether a fat is solid or liquid at room temperature.

Classification of fats

Fats that contain no double bonds in any of their R chains are referred to as saturated fats. They are called "saturated" because they contain as many hydrogen atoms as they possibly can. These fats tend to be solids at room temperature, and come from animal sources (for example animal fat and butter).

Unsaturated fats, in contrast, do contain double bonds in their structure. They are unsaturated because they do not contain as many hydrogen atoms as they could. They tend to be liquid at room temperature and normally come from plants and fish. They are usually called "the oils". Unsaturated fats can be further classified according to their number of double bonds:

• Monounsaturated fats contain only one or few double bonds along their R chains, so they can accommodate at least one more hydrogen atom. These types of fats include olive oil and peanut oil.

• Polyunsaturated fats, however, contain many double bonds, so can accommodate many more hydrogen atoms in their structure. These types of fats include sunflower oil and corn oil. Caution needs to be taken with these polyunsaturated fats because they are likely to become rancid at room temperature.

Although both the mono and the polyunsaturated fats are liquid at room temperature, the monounsaturated fats, because of their high proportion of saturated fats, will turn cloudy and start to solidify at refrigeration temperatures because the areas of saturated fats contained in the structure will begin to congeal.

Hydrogenation:Hydrogen atoms can be artificially added to polyunsaturated oils in a process called hydrogenation. This is used to make food products that are more solid and become less rancid at room temperature, such as margarine.

Solubility in water

When liquid fats are added to water, the two liquids will not mix. This is because fats are neutral, so are not attracted to the water molecules. If oil and water are mixed, the oil will rise to the surface and float because it is less dense than the water. In order to make a stable fat/water mix, surfactant molecules (molecules that contain both hydrophobic and hydrophilic parts) are needed. A common example of a surfactant molecule is a detergent molecule, which is used to remove fat stains from clothes – the water insoluble part of the detergent inserts into the grease stain, leaving the water soluble part in the washing water, so the grease stain can be removed into the water.

Effect of heat

Gentle heating

Fats, unlike water, are very susceptible to small changes in heat (water does not change significantly on heating it between 0 °C and 100 °C, although at 0 °C and 100 °C exactly very significant changes occur). Heating up to their boiling point will reduce the fluidity of a fat source, whereas cooling to its freezing point will cause a gradual increase in viscosity. This is because different parts of the fat molecule will melt at different temperatures, so the whole molecule is not as uniform as molecules of water in a water solution, where each molecule will boil at exactly the same temperature.

Boiling

The boiling temperatures of fats are much higher than the boiling temperature of water, and range between 260 °C and 400 °C depending on the fat source. For example, the boiling point of olive oil is about 300 °C.

However, fats will begin to decompose at temperatures well below their boiling points. This will begin at a temperature called their smoking point. For example, the smoking point of olive oil occurs at around 200 °C. A smoking point can be detected by the release of smoke (seen as visible fumes) and discoloration of the oil. The fats will start to decompose.

Several new chemical compounds are formed during this decomposition – mainly oxidised triglycerides (e.g. acrolein), and coloured compounds. The higher the composition of unsaturated fats, the lower the smoking point, so the more toxic compounds (like acrolein) are produced on heating to the same temperature.

Fats being used to fry need to be heated to at least 180 °C. Thus only certain oils are suitable for frying. Oils that are good for frying include refined oils, such as vegetable oils, which work well because their smoke points are above 200 °C. Unrefined oils however, such as extra-virgin olive oil, should not be used for frying because their smoke points are below 180 °C. Equally, frying oil should not be reused more than three times because the smoke point of any oil will decrease with use. Heating oil to too high a temperature is also unadvised because at high temperatures, the fat source may release flammable vapours that cause it to spontaneously ignite.

Role in food

Fats have a very important role in providing flavour. Many molecules responsible for the flavour of foods are hydrophobic and are thus carried in the fat component of the food.

The presence of fats in food also improves the texture and "mouthfeel" properties of foods.

Fats are also used to cook with instead of water. The advantage of using fat as the cooking liquid instead of water is that the temperatures that can be reached are much higher than can be reached when cooking in water, where the maximum temperature reached can only ever be 100 °C, so reactions that need high temperatures to occur, such as the Maillard reactions responsible for the colour and tastes of most fried/sautéed meats, can occur much more rapidly.

Also, the fats are good conductors of heat. This means that using them will reduce the cooking times of foods, and this is why vegetables or pieces of meat to be grilled are often oiled first to improve contact and heat conduction between the frying pan and the meat/vegetable source.

What should be known about culinary ingredients: Complex carbohydrates

Complex carbohydrates are also made up of sugar units, but in complex carbohydrates many more sugar units are joined together, forming longer, more complex chains. This group of carbohydrates is therefore also known as the polysaccharides.

Solubility

In complex carbohydrates, many of the previously available OH groups in the sugar units have been involved in glycosidic bonding, so the complex sugars are much less soluble than the simple sugars. There are fewer free OH groups available (more are involved in glycosidic bonds) to bond with water molecules, so solubility is less.

Digestibility

Due to their more complex structure, these carbohydrates take longer to be digested than simple carbohydrates, and so act more as a long-term energy store. Cellulose, one of the complex carbohydrates, has such a complex structure that it cannot be digested at all, and it actually passes through the entire digestive system unaffected.

Classification

Complex carbohydrates are synthesised by plants, and thus are found in plant sources. Complex carbohydrates include two main groups – the fibres and the starches. The fibres are major compartments of cell walls, and the starches are found located in small granules inside the cells. The two groups have very different properties, despite both being complex carbohydrates, and will therefore be considered as separate groups.

Fibres

The main fibres found in cell walls are cellulose, pectin and hemicelluloses. Each has a slightly different structure, and this affects how they behave with heating and pH.

Culinary role:Plant cell walls have an important role in determining vegetable and fruit texture. Understanding how each of the cell wall components reacts in the presence of heat or pH is thus very useful in understanding and trying to control changes in vegetable and fruit texture on cooking. Pectin acts as the glue to hold the cell wall together, and thus tends to play the most important role in determining fruit and vegetable texture.

CelluloseCellulose is made up of long straight chains of glucose molecules. The absence of side chains allows cellulose molecules to lie closely together and form very rigid structures.

Effect of heat: Unlike the other fibres, cellulose is not chemically broken down by heat or pH.

HemicelluloseHemicellulose is a polymer consisting of several different simple sugars (including glucose, xylose, mannose, rhamnose, arabinose and galactose).

Effect of heat: During cooking the hemicelluloses will break down into their constituent sugars.

PectinPectin is another polysaccharide made up of many molecules of α-Galacturonic acid, a sugar unit that resembles a modified glucose unit.

Effect of heat: In the presence of heat, these large chains are chemically degraded into soluble molecules, which are released from the cell wall, helping the cell wall to break down. In addition to heat, pH plays an important role in pectin degradation.

Effect of pH: In the presence of alkali, the degradation of pectin due to heat is much more pronounced. Alkali causes the ionisation of the COOH groups, to form COO⁻ groups, which will repel each other, favouring their separation and release from the cell wall.

Acid however, strengthens pectin. In an acidic environment, any COO⁻ groups will acquire hydrogen ions, to form neutral COOH groups, and the pectin molecules will remain neutral. This reduces repulsion between pectin molecules, so they will tend to stay associated and be prevented from degrading so readily when heated.

Starches

There are two main sorts of starch molecule found in vegetables: amylose and amylopectin. Both are composed of long chains of glucose molecules, but they differ in how the glucose molecules are linked together.

Amylose exists as a long unbranched chain of glucose molecules, containing usually between 250 and 2000 glucose molecules. It is found coiled in the shape of a helix.

Amylopectin chains however are highly branched, with short side chains of about 30 glucose units attached regularly along the chain. Amylopectin molecules are therefore much larger, and may contain up to two million glucose molecules.

The starch found in food often contains a mixture of these two molecules, but the amylopectin usually accounts for the majority of the starch (between 70 and 85%). The exact ratio of amylose to amylopectin will depend on the food source from which the starch is extracted, and since the amylose and amylopectin molecules behave in slightly different ways, starches derived from different plant origins will behave slightly differently.

Culinary role:The primary culinary role of the starches is as thickening agents. In the presence of water or any liquid, these long starch molecules will evenly disperse themselves throughout the liquid, and will therefore reduce the ease with which the water molecules contained can move around each other. The liquid will therefore flow less easily, and will become thicker. If the appropriate conditions are met, these starch molecules will join together to form an extensive network, which can actually trap the water molecules, making the liquid slightly solidify or gel. This is similar to the way that denatured proteins can be used to retain the water in food systems and help keep food sources more juicy. Over time, the network will become stronger and stronger as more bonds are made and the network gel will start to squeeze out water in a process called syneresis.

Starch is derived from plant tissue, where the starch molecules are organised into small structures called granules, in which the starch granules are very tightly bonded together and this structure can only be disrupted and the starch released in the presence of moist heat. In starch granules, the amylose and amylopectin molecules are held closely together as granules. Microscopes have shown us that these starch granules contain circular layers of amylopectin and amylose molecules held together by hydrogen bonding.

The more amylose present in the starch granules, the more strongly the granule will be held together, and the harder it will be to disrupt. This is because the unbranched amylose molecules can bond together in a much more compact fashion.

Effect of heat and pH:Like all large molecules, the starches are broken down into their constituent units (the glucose molecules) by strong heat and acid.

However, as already mentioned, the starches found in natural food sources are actually located in small compartments known as starch granules inside the plant cells. These granules act to some extent to protect the starch from degradation and damage. However, the starch needs to be released from these granules before it can act as a thickener, and this process requires heat. Once the starch has been released from these granules, it can be broken down by extreme conditions such as heat or acid in the same way as most other biological molecules.

Technological applications of Molecular Gastronomy in a three stars restaurant.

Relations science / culinary art.

Antoine MATHURIN, Audrey TARDIEU, Hervé THISINRA Group of Molecular Gastronomy, Paris

I. Application of Molecular Gastronomy in the kitchen

Many cooks (Pierre Gagnaire, Paris / London / Tokyo; Ferran Adrià, Roses; Heston Blumenthal, London; Emile Jung, Strasbourg; and others...) look ceaselessly for new recipes and for new techniques. Being the science that studies cooking (and more) from a chemical and physical point of view, Molecular Gastronomy produces new knowledge on this activity, and, henceforth, can have educational and technological applications in the kitchen.

In particular scientific knowledge can be applied in the three following fields: culinary tools, culinary ingredients and culinary methods. As a consequence, technological transfer from Molecular Gastronomy to the chefs enriches the culinary practice and leads to new dishes.

A collaboration between the INRA Group of Molecular Gastronomy and Pierre Gagnaire's restaurants (Rue Balzac, Paris; Gaya, Paris; Sketch, London, Pierre Gagnaire in Tokyo, Tokyo) has been established since 1998: ideas from Molecular Gastronomy are given to the kitchen team, on a monthly basis. The results of these works are both produced as dishes in the various restaurants and displayed on Internet both in French and in English (http://www.pierre-gagnaire.com) and are linked to the INICON project. Therefore, the various "Science and cooking" pages of this Internet site should be considered as results of INICON as well.

A closer technological link was established within the European INICON Programme those last 3 years, in order to improve technology transfer from the INRA Group of Molecular Gastronomy and these restaurants.

More exactly, the aim was to put into daily production new techniques proposed by Hervé This to Pierre Gagnaire. The purpose of the studies was to identify the important parameters involved in the "making of a recipe", then to make it (real systems). Eventually, in order to be able to apply the techniques from the laboratory in the restaurant, it was necessary to take into account both all the parameters of the restaurant and team organization, and the experimental conditions of the techniques.

The results obtained are given here in a chronological order. In practice, first the questions from the kitchen team had to be solved (more "important"), and only later it has been possible to study the application of technological ideas. The relative importance of the various particular studies is difficult to assess, because of the rapidly changing environment of this particular restaurant: at Pierre Gagnaire's, the menu is changing very fast, and dishes are almost never the same, day after day.

For the restaurant, the aim of this project was to introduce new techniques and new products (ex: phenolic compounds from grapes, food (dietary) additives, gelling and thickening agent, liquid nitrogen, dry ice) and to elaborate technical index cards, summarizing the results of each experiment.

The process used for each study was the following:

1. Definition of the technical model:a. Model adaptation for the restaurant.b. Presentation of the technique and discussion with the Chef and his team.c. Modification of the technique according to advices of the Chef.d. Validation of the technique and training of the crew.

2. Data compilation (results of experiments, contacts).

3. Sharing of knowledge with the Chef about physical and chemical mechanisms connected to the kitchen.

4. Showing to the team of the restaurant a new approach of the kitchen, its reasoning and its knowledge.

5. Educating the staff in the practice of the transferred techniques.

6. Strengthening the synergies between the Molecular Gastronomy and the art of cooking.

7. Widen the communication and the dialogue between both domains.

III.1. Jellified pearls

III.1.1. Objective:The aim of this study is to give new sensations to the customer by using spheres with a gel (of gelatine or agar-agar, for example) trapping a liquid. When such spheres are chewed, the gelatine skin offers first some mechanical resistance, and then, becomes a tender gel at the same time that the liquid is released.

III.1.2. Introduction:A gel is a liquid phase dispersed in a continuous solid phase. Usually, in food, the dispersed phase is an aqueous solution, and the solid continuous phase has to be constituted with bound proteins. To make "jellified pearls", we use a gel to trap a liquid in it. The gel can be obtained using gelatine or another gelling agent, but gelatine is particular because its melting point is well adapted to eating (around 36 °C, depending on the kind of collagenic tissue that was used to extract gelatine).

H. This had the idea that pearls with a liquid core and a jellified membrane could be obtained through dipping some frozen aqueous solution into a concentrated solution of gelatine. Being cooled by the frozen core, the gelatine solution would gel around it, making a jellified envelope around it. Put in the plate, the aqueous solution would become liquid again and this liquid would be trapped into a jellified pearl.

III.1.3. Balls of ice coated by gelatine at 1.2 %:

III.1.3.1. Material:

• Pacojet.

• Spoon for sherbet or Parisian spoon, diameter 1 cm ± 0.1 cm.

• Dishes: pan, tubs.

• Tap water: we made the hypothesis (to verify) that we shall obtain a good result with tap water, because there are no strong interactions between gelatine and the ions contained in the tap water.

• Gelatine or Agar-agar, supplier Louis François.

• Deep freeze Koma (system 80/20); beach 40 in +40 °C; constant T °C -30 °C.

• Cold room Dagar brand with constant temperature at 2 °C; precision 2 °C.

III.1.3.2. Method:

1. Put some water (beforehand frozen) in the ice-cream maker to obtain a "sherbet".

2. Form balls with the Parisian spoon.

3. Put them in the deep freeze so that the temperature of balls is kept between -15 and -25 °C.

4. Make a solution of gelatine at 1.2 % in weight with sheets of gelatine previously dipped into some water at room temperature.

5. With a chocolate fork (two teeth), plunge the balls of sherbet into the solution of gelatine, and remove them after less than 5 s. The sherbet quickly cools the solution of gelatine in contact and thus, the gelatine sets in gel, making a film around the ball of sherbet.

6. Let flow the excess of gelatine.

7. If the coat of gel is not enough, repeat steps 5 and 6.

8. Put the balls in the fridge, until the sherbet balls are liquid.

III.1.3.3. Results:With these experimental conditions (solution of gelatine in water at 12 g/L at room temperature and cold ice balls) the pearls of gelatine didn't set. The gelatine didn't form a complete skin around the ball.

III.1.3.4. Discussion/Interpretation:The first tests did not succeed: either the concentration in gelatine was too low, or the difference of temperatures between the balls of sherbet and the solution was not important enough.

The experiments were repeated using a higher concentration in gelatine with better results.

III.1.4. Balls of ice at very low temperature, coated by 1.2 % gelatine:

III.1.4.1. Material:The material used is the same as in the first experience.

III.1.4.2. Method:The ice balls are kept in a deep freeze at –25 °C. Also, to form the balls, the solution of gelatine is used at room temperature.

III.1.4.3. Results:All the ice balls are coated with gelatine, but the film is not homogenous. Then, some liquid can pass through the film of gel, which is fragile.

III.1.4.4. Discussion/Interpretation:The technique seems to work, even if the gel doesn't coat all the surface of the ice balls. Also, a film of water is created when the ice ball, in contact with the gel, melts.

To improve this technique, the gelatine concentration can be higher, in order to have a more viscous film, which could stick more easily to the ice surface. Also, some flour can be added on the ice balls before being dipped in the solution of gelatine. This would increase the contact between the gel and the ice and thus the gel would set homogeneously.

III.1.5. Balls of ice, coated by 2.5 % gelatine.

III.1.5.1. Material:The material used is the same as in the first experience, but the gelatine solution is now increased at 2.5 %.

III.1.5.2. Method:One new step is just added to method used above: the step 4') consists in rolling the balls of ice in flour, to form a film on their surface.

III.1.5.3. Results:Balls of gelatine did not set, and the film was still not homogenous. The use of the gelatine doesn't seem to be the right solution. On a visual point of view, the surface is not smooth and non-homogenous; and the flour makes an opaque and irregular coating.

III.1.5.4. Discussion/Interpretation:At room temperature, the solution of gelatine doesn't set in a homogenous way and cooled, it sets too fast and becomes a breakable gel. Agar-agar could be an alternative.

The use of the flour does not improve the results, it gives pearls of insufficient optic.

III.1.6. From a recipe of the restaurant Pierre Gagnaire:

Balls of marzipan (8 mm of diameter) are coated with a solution of "blackcurrant agar". The preparation is the same as before, but here, the inside of the ball (marzipan) is solid at room temperature.

III.1.6.1. Objective:The aim of this experiment is to obtain a smooth appearance, by using a cellophane film to avoid the irregularities of the mould.

III.1.6.2. Material:Recipe of "blackcurrant agar":

• 150 g of frozen blackcurrant (extract the juice and pass it in a conical strainer)

• 500 g of water

• 100 g of sugar

• 13 g of agar, supplied by Louis François

• 50 g of blackcurrant liqueur.

III.1.6.3. Method:

1. Make a syrup with the water, 80 g of sugar, the blackcurrant juice and the blackcurrant liqueur.

2. Put this mixture to the boil.

3. Mix 20 g of sugar with agar-agar, and sprinkle over the syrup, while shaking strongly the solution to avoid lumps.

4. Shake the preparation from 3 to 4 minutes.

5. Roll the marzipan ball in the solution of "blackcurrant agar".

III.1.6.4. Results:Nine balls on ten set correctly.

III.1.6.5. Discussion/Interpretation:The "blackcurrant agar" is stickier and thicker than the former solutions. As it flows slowly on the balls, the contact with the cold source is longer and allows to get a homogenous gel. To have a solid, smooth and homogenous coating, the balls can be dipped several times into the agar solution.

Done with such a gel and ice balls, the thickness is satisfactory, and the heart remains liquid and trapped in the coat of gel. However, air bubbles appear in the liquid inside the jellified film. These air bubbles come from whisking with the Pacojet. Using ice cubes instead of ice made with Pacojet may prevent this bubble formation.

III.1.7. Tests to make balls of ice:

III.1.7.1. Material:

• A tasty juice or a sauce.

• Flour.

• Toothpicks.

• Bowls: tubs.

• Tap water.

• Agar-agar supplied by Louis François.

• Cellophane.

• Deep freeze Koma (system 80/20); beach 40 in +40 °C; constant T °C at –30 °C.

III.1.7.2. Method:

1. Design half sphere shapes with a sherbet spoon on a Cellophane film, put on flour.

2. Flow some water in these prints, and place toothpicks towards the half sphere.

3. Put them in the deep freeze.

4. Make complete spheres once the half spheres are frozen (by rubbing them slightly with the finger to make the ice melt and put them in the deep freeze).

5. Dip them in the blackcurrant agar as in III.1.6.3.

III.1.7.3. Results:Seven balls on ten were set correctly.

III.1.7.4. Discussion/Interpretation:The technique of two ice cubes joined together around one toothpick works, but the moulds are imperfect. Also, it is hard to get a perfect flat surface of the half spheres and thus it is difficult sometimes to stick them together.

The solution of agar-agar (at 1.3%) coats correctly all the balls. The film, thinner, is well appreciated because it is less "doughy" in the mouth. However, the solution of agar sets around the balls with more difficulties. Indeed, the ice cubes show a smoother surface than a sherbet. This implies a smaller contact area between the ice and the agar gel.

There are no air bubbles in the heart of the balls when we let the ice cubes melt. Also, the agar-agar gel can resist to the loss of volume due to ice melting. The shape of the ball remains spherical, which is much appreciated.

According to the Chef, the size is good, and no change is needed.

Finally, this gel is appreciated for its translucent side; it gives an additional aesthetic touch.

An idea of the Chef would be to add a chocolate coating on the film of gel, to bring a crispy touch to the pearl.

III.1.8. Addition of a chocolate coating:

III.1.8.1. Materials:The material used is the same as in III.1.7. with white chocolate, for example.

III.1.8.2. Method:One new step is just added to method used above: at the end, dip the balls into some melted white chocolate.

III.1.8.3. Results:Here, 6 balls on ten were successful. The liquid heart is appreciated because it brings some coolness to the chocolate.

III.1.8.4. Discussion/Interpretation:The main issue of this technique is the manufacture of the ice balls and to get a good size. A test with a salty paste didn't give good results in terms of size.

However, from a technical point of view, these spheres can be done without any gelatine and thus this doesn't make a particular technical progress. Is there any influence of the gel from a taste point of view?

III.1.9. Setting of the technique in the restaurant:

III.1.9.1. Material:The gel:

• 1 l of "water of tomato" (press some tomatoes, get the juice without the pulp and the colored pigments)

• 80 g of agar-agar

• 4 gelatine leaves (Rousselot)

The liquid:

• Juice of tomatoes with aromatic herbs (thyme, rosemary, tarragon, basil, oregano).

• 1 stamp of 3.5 cm of diameter (precision 0.01 mm)

• A pan

• A kitchen marble.

III.1.9.2. Method:

1. Make 1 l of a solution of water of tomato and add 80 g of agar-agar and 4 sheets of gelatine.

2. Make a 2 mm thick film with the former mixture (at 50 °C) of "water of tomato".

3. Place frozen half spheres (2.5 cm in diameter) of tomato juice on the film, and flatten their top.

4. Pour the mixture on the top of the frozen spheres in order to cover them completely.

5. Stamp the obtained dishes out.

III.1.9.3. Results:During this test, we obtained 9 jellified tomato ravioli out of 10. Their shape is regular and smooth; they have a pleasant colour, and their manipulation is easy. The ice cubes are perfectly trapped and the agar-agar gel keeps the round shape while the ice is melting.

III.1.9.4. Discussion/Interpretation:Although easier to use, sometimes the two layers of gel don't stick together and split up while they are used. Is it a problem of gel concentration or a problem of sticking? We tried first to use some gelatine instead, but it neither worked. We tried to mix a solution of gelatine with one of agar-agar but these two solutions didn't mix well together.

III.1.10. Assessment:

III.1.10.1. Evaluation:This last method remains the most effective in terms of use for the restaurant. Indeed, the joint between two films of gel is satisfactory, and the manipulation is still practical during the service. This technique can be realized in two times, where the tomato ice and the gel can be made in advance (concerning thermoreversible gels). Further, the ravioli can be made and stored at low (but positive) temperature in the fridge without any problem.

However, the manufacture of spheres is abandoned for practical and aesthetic reasons. Indeed, it is difficult to get a nice spherical ball of ice.

III.1.10.2. Conclusions:This technique is used in the restaurant, in the Tasting Menu. It is easy to realize in the restaurant kitchen and the customer's opinion is good.

This technology transfer took 5 weeks and one more week was needed to find a dish using it. It is interesting to note that the final result does not correspond to the initial tests because of the technical evolution during the different tests and the Chef's point of view.

III.1.11. Other suggestions openings, ideas, applications of the technology:This technique allows to trap a liquid into a solid phase (gel). It works with any liquid which freezes and which melts at ambient temperature.

However, the technique of trapping a liquid inside a solid is already known in the chocolate or toffee factory. Here, for sweet balls, the interest could be in coating the soft gelatine film with chocolate, to bring a crispy sensation.

In the case of salty balls, another use could be some minced meat inside a gel, like ravioli.

III.2. Fusion of "cheveux d'ange"

III.2.1. Objective:"Cheveux d'ange" (angel hair) are threads obtained by pastry chefs by vitrification of mixtures of glucose, sucrose, water and colouring agent.

The objective of the work was to know how to "melt" (is it fusion or dissolution?) these products by adding some warm solution (in this particular case, some coffee) on them.

III.2.2. Materials and method:

• Some threads of "cheveux d'ange"; 0.4 mm of diameter (precision 0.029 mm).

• Thermocouple MAFTER typifies K, range 50 – 950 °C; precision 1 °C.

• Water.

• A Kofler hot bench, Mettler 10; precision 0.5 °C.

• Stopwatch (precision 1 s).

III.2.2.1. Rate of dissolution at different temperatures:

1. Put to the boil a big volume of water (we chose an important volume so that its temperature is approximately constant during the experiment, because of its thermal inertia), and let it cool slowly.

2. Control the temperature of the liquid with the thermocouple.

3. Dip samples of threads into the cooling water, by step of 5 °C, observe the "melting" and measure the rate of "melting" (in the ranges of temperature where a change of behaviour occurs, we make the measure every 2.5 °C).

III.2.3. Results:III.2.3.1. Measure of the speed of dissolution at different temperatures:(Cf. annexe 3)

We observe that the dissolution of "cheveux d'ange" plunged into water is never immediate; however, stirring the solution helps this dissolution.

The graph shows that the water temperature has an influence on the dissolution: the higher the temperature, the quicker the dissolution.

III.2.3.2. Measure of the melting point of "cheveux d'ange":The melting of "cheveux d'ange" begins at 100 °C and is complete at 120 °C.

III.2.4. Discussion/Interpretation:The melting of "cheveux d'ange" occurs between 100 °C and 120 °C. Indeed, the cheveux d'ange material is not pure. However, it is not the fusion which takes place in this phenomenon but a dissolution of the toffee in solution, because the melting point is superior to the temperatures we used.

The size of the "cheveux d'ange" (their diameter) and the temperature of the solution influence the dissolution kinetics. Also, because the disappearance in solution of "cheveux d'ange" was realized with some tap water, it is probably important to take into account the solution concentration to be able to estimate the speed of dissolution and the efficiency of the solvent at a given temperature. However, a mechanical agitation can largely facilitate the dissolution.

To improve the dissolution, we can increase the time of contact between the solution and the threads; for example make flow our liquid with a smaller outflow. We can also accelerate the process of dissolution by adding a mechanical disturbance to the solution; for example, stirring the solution with a spoon.

III.2.5. Conclusion:When we pour some warm water on "cheveux d'ange", the phenomenon involved is the dissolution. To improve it, there are 3 different ways: higher temperature of the solution, smaller diameter of the "cheveux d'ange", or stirring the mixture.

III.2.6. Other suggestions/ openings, ideas, applications of technology:To get a better dissolution of the "cheveux d'ange", we can also increase the contact with the water, for example by putting them in a big volume of water.

III.3. Red mullet scales

III.3.1. Objective:The aim of this study is to extract flavours and particular tastes of the scales of red mullet, by extracting in oil and in water respectively hydrophobic and hydrophilic molecules. The method is the same as in bisques, realized with shells of lobster and other sea product.

III.3.2. Introduction:Fish scales constitute the external skeleton of fishes or dermic skeleton. They have a role of epithelium, external skeleton, and protection. As any structure of support (chondrichthyans), scales are compact structures through a process of calcification and ossification. Scales possess a superior coat of osteoblasts, which help the calcification of proteins, constituted by fibres of collagens and by microfibrils of actin (produced by the fibroblasts).

These fibroblasts synthesize fibres of collagen as an extension of the cytoskeleton, coats of fibres are planned in the same direction since centromeres towards the suburb, the microfibrils of actin are also set at the same time as these fibres.

A folding of these coats is made with a rotation of the orientation of this protein synthesis, at the rate of an angle of 90° by folding. This intertwining of protein tubes forms a complex labyrinth of collagen and actin; the compaction is pronounced. (These bridges have a length of 0.4·10⁻⁷ m and a width of 0.2·10⁻⁶ m).

A process of calcification takes place by the osteoblasts of the superior coat which put down crystals of calcium along these tubes of protein. These two phenomena are continuous, there is no difference and precise border between the calcified coat and the only protein weft.

In practice, the scales of fishes are mainly constituted by a network of proteins (collagen and actin), covered with calcium. The aim of this experiment is to extract the taste and odorant molecules produced by thermal treatment of the scales. However, the availability of these molecules is unknown.

We tried first to extract hydrophobic molecules by cooking some scales in oil. In a second time, we cooked them in water, to extract the hydrophilic molecules.

III.3.3. First test of cooking scales:

III.3.3.1. Material:

• 100 g of scales of red mullet. (3 kg of red mullet (9 fishes) give 95 g of scales).

• Sunflower oil.

• Water, salt, pepper.

• A copper pan with its lid.

III.3.3.2. Method:

1. Heat 5 mL of oil in the frying pan (without burning it).

2. Roast the red mullet scales for 1 min.

3. Add 50 mL of water, salt, pepper, and cover with the lid (not to lose any molecules which could evaporate).

4. Cook the mixture for 3 hours over a medium heat, with the lid.

III.3.3.3. Results:

• At t + 1 min: before adding some water, the oil doesn't have any taste of red mullet scale. The texture is not crispy but rubbery.

• At t + 10 min: characteristic fat smell and taste of fishes, but no particular flavour of red mullet.

• At t + 20 min, t + 30 min, t + 60 min, t + 180 min: same taste, with unpleasant texture of scales. The juice doesn't have any significant taste.

When some scales were cooked for 6 hours, neither the scales nor the stock had any interesting flavour.

III.3.3.4. Discussion/Interpretation:The quantity of scales may be not important enough, but providing the restaurant in scales becomes then a problem with regard to the numbers of red mullets used.

The cooking time seems to be long enough. After 6 hours, the flavour of red mullet is not strong enough, the stock doesn't have any particularity: just a flavour of fish, not red mullet.

In order to improve the extraction of taste molecules, an identical experiment is realized. This time, the scales are completely covered with water.

III.3.4. Second test:

III.3.4.1. Material:Same material as in III.3.3.1.

III.3.4.2. Method:Here, we roast the scales (100 g) in tasty oil and we boil them in water (½ L) for a long time (about 6 hours) to extract a maximum of flavoured molecules. To test the stock, the floating fat is removed.

III.3.4.3. Results:The broth obtained in this second experiment is tasteless, with no particularities compared to a common fish stock.

Concerning the scales, a tiny red mullet taste is obtained, but no recipe could be done with them.

III.3.4.4. Discussion/Interpretation:No flavour molecules were released even after 6 hours. A hypothesis could be that these flavour molecules can be trapped in the inorganic network. We suggest to break up the calcium by using white vinegar in a marinade.

III.3.5. Marinade with white vinegar:

The goal of this experiment is to facilitate the release of the organic molecules by making a marinade in white vinegar, to weaken the inorganic structure of the scales.

III.3.5.1. Material:

• 100 g of scales of red mullet.

• ½ l of white wine vinegar.

• Groundnut oil.

• Water, salt, pepper.

• A copper pan with its lid.

III.3.5.2. Method:

1. Put the scales of red mullet in the white wine vinegar.

2. Soak it for minimum 48 hours, taste it.

3. Follow the method in III.3.3.2.

III.3.5.3. Results:The stock obtained using this new method didn't have a particular or original flavour. The flavour of red mullet is not strong enough for the Chef. The use of white wine vinegar is not relevant.

III.3.5.4. Discussion/Interpretation:This experiment doesn't seem to allow to extract the flavour molecules from scales. Either these molecules weren't extracted, or they were not concentrated enough to be detected in a broth. Also, the vinegar may have not reacted enough.

Furthermore, this technique requires to remove the scales from the skin and to treat them, which adds a supplementary task to the team of the restaurant. Also, sauces based on fish remains are already employed in restoration and give more decisive and faster results to operate.

III.3.5.5. Evaluation:The scales can't be in a dish because of their rubbery texture and their non-original taste.

The flavour of the stock (100 g of scales in 500 ml of water) is not strong enough. The solution could be a stock made with more scales, but these experiments were done with the quantity of red mullet scales supplied by the red mullets used by the restaurant.

The tests didn't show the presence of particular flavour molecules in the scales. Even the maceration in the vinegar didn't show any result. The methods may be improved by a longer cooking time, higher quantities of scales or water. Also, scales can be crushed into powder, in order to make the extraction easier.

III.3.6. Conclusion:These experiments did not give any useful result for the restaurant. Concerning the flavour molecules from the scales, other tests have to be done, using bigger quantities in order to be able to conclude about their possible extraction.

The scales can't be used as a dish, but they can be an element of the dish, like a stock, decoration. Their purpose would only be to give some flavour to the fish.

III.3.7. Other suggestions openings, ideas, applications of the technology:Serve as decoration with a mixture of water and flour around red mullet.

Scales don't seem to bring a significant taste or smell. However, it can be used with skins and other giblets of the fish in the preparation of sauces.

III.4. Wave guide in gels

III.4.1. Objective:The purpose of this study is to elaborate a wave guide, with gels of various colours, which concentrate the light of a candle, in order to celebrate the "annus mirabilis", 2005, the "year of physics" (one century after Albert Einstein's study of photoelectric effect).

III.4.2. Introduction:

III.4.2.1. Law of Snell-Descartes:The principle of the wave guide is included into the laws of Snell-Descartes (René Descartes, 1596–1650) in geometrical optics. It is inspired by the third law on the principle of the refraction and the critical angle of incidence according to the formula:

n₁ sin(θᵢ) = n₂ sin(θᵣ)

A wave guide concentrates the rays of light in an environment of index n₁, in another environment of index n₂ < n₁.

The rays of light, which come to the environment of index n₁, penetrate into this environment. In contact with the index n₂, a part of the rays is reflected by this environment, and the other part is refracted.

However, when the incidence angle is higher than the critical incidence angle, the rays are totally reflected. We can calculate this critical incidence angle according to the values of the indexes of the different environments. By definition, the critical incidence angle is an angle θᵢ such as θᵣ = π/2 radians, then sin(θᵣ) = 1. We deduct the critical angle of incidence from it:

θᵢ = arcsin( n₂ / n₁ )

Each time that a ray from the environment of index n₁ comes to the border made with the other environment of index n₂, with an incidence angle higher than the critical incidence angle, this ray will be concentrated in the environment of index n₁. We can obtain a wave guide.

Finally, the bigger the index difference between two environments, the weaker the critical incidence angle.

III.4.2.2. Our wave guides:The wave guides we wanted to obtain will have two different index values. We wish to make some parallelepipedal shape with a cylinder inside, playing the role of the second environment. The index of the internal environment (cylinders) must be higher than the one of the parallelepipedal shape.

We wish to realize these two environments in gels. To obtain an index difference, we just have to change the gel concentration: the more concentrated the gel, the higher the index.

In the case of a gel made from 1 % gelatine in water, we estimate that the index would be similar to the one of a solution of distilled water, in the standard conditions of temperature and pressure.

n_gel = n_water = 1.33335 (precision 10⁻⁵).

Calculation of the critical incidence angle:n_gel = n_water = 1.33335; n_air = 1.θᵢ = arcsin(n_gel / n_air) = 48.59°.

III.4.3. First test of a wave guide.

III.4.3.1. Material:

• Stamps in stainless steel with parallelepipedal shape (8 x 4 x 4 cm).

• Water.

• Gelatine leaves supplied by Louis François.

• Agar-agar supplied by Louis François.

• Plastic tubs.

• Cardboard and aluminium foil.

III.4.3.2. Method:Two tests are done, one with some gelatine, one with some agar-agar.

1. Make a cardboard cylindrical stamp (length = 8 cm, diameter = 1.5 cm) and cover it with aluminium.

2. Make a solution of gelatine or agar-agar at 1.2 %.

3. Pour this solution in the parallelepipedal stamp where the cylindrical stamp is placed.

4. Place the mould in the fridge and wait for gel formation.

5. Turn the gel out of the tin.

III.4.3.3. Results:The two different gels set properly at 12 g/L, but with gelatine, it is not easily manipulated as it breaks easily. Thus, the gelatine won't be used anymore.

Also, the stamp is too big to be used in the restaurant. It is necessary to reduce its dimensions and a new test is realized with a smaller stamp (3 x 3 x 7 cm).

The technique however works, as we observe a concentration of the light on the internal cylinder.

III.4.4. Smaller stamps.

III.4.4.1. Material and method:The same method is used as in III.4.3.1. with smaller shapes.

The gels are realized with agar-agar according to various concentrations: 0.5 %, 1 % and 2 % to determine the best texture given by the concentration.

The solution is put in the parallelepipedal stamp and when the gel is set, the guide of waves is done by cutting the cylinder with a specific tool.

III.4.4.2. Results:The solution flows with difficulty into the stamp and some air bubbles remain in the gel.

III.4.4.3. Discussion/Interpretation:The use of the agar-agar and the other similar gelling agents does not give satisfactory results because the solution isn't translucent, which is useless for a wave guide.

Furthermore, the cylinder made this way is too irregular. Finally, the size is still too big to be used in a dish.

The restaurant uses very concentrated gels of gelatine for a cheeseboard: a solution of gelatine made of 50 leaves in 1.5 l of water (the final gelatine concentration of the solution is 200 g/L) is put in a glass (champagne glass). It gives a translucent solid on which some cheese is put. The manufacture of the gelatine is already mastered by the team of the restaurant. New tests are realized on the basis of this preparation.

III.4.5. Realize a gel with a solution of gelatine at 200 g/L:

III.4.5.1. Material and method:

• Stamps in stainless steel with parallelepipedal shape (14 x 14 x 70 mm).

• Water.

• Gelatine supplied by Louis François.

• Food colouring agents.

• Plastic tubs.

• Plastic straw (diameter of 0.7 cm).

• Pour some solution of gelatine in the stamp (vertical) to make a waterproof film at the bottom.

• Put a straw at the bottom of the gelatine film and stick it vertically.

• Fill the stamp with the remaining gelatine.

• Place the mould in the fridge the time to make the gelatine take in gel.

• Turn the gelatine guide out of the mould by means of some warm water poured on the outside of the mould.

III.4.5.2. Results:The gel sets and has a solid consistency. It is translucent and the light penetrates; this is not a "wave guide".

III.4.5.3. Discussion/Interpretation:The gel made with a solution of 200 g/L is very sticky. It has a very firm texture and is translucent, which is appreciated by the Chef.

The technique with a metallic stamp and a solution of gelatine at 20 % is technically used by the team of the restaurant. It is then easy to put into practice.

The gel is difficult to turn out of the mould. The use of hot water helps but weakens by melting the surface of the gel. We obtained better results with a thinner straw (5 mm of diameter), giving a thicker border of gel.

These cylinders can be used in a dish with an edible candle. They have to be well placed, away enough not to melt (at 4 or 5 cm from the candle light). Although, this dish has to be served quite quickly, it can't be prepared in advance (do not exceed 20 min on average).

III.4.6. Gel of lemon with effervescent powder inside.

III.4.6.1. Objective:We would like to get an aesthetic gel (looking like a "wave guide") in which we would pour a mixture of effervescent powder in order to create a candy with a foaming effect.

This experiment is to be put in correlation with the technical index card n°9 on effervescent powder.

III.4.6.2. Material and method:

• 250 g of lemon juice.

• 50 g of gelatine (to get a solution at 200 g/L).

• 50 g of sugar.

• Mixture of effervescent powder (Cf. N°10).

• The tubes of gelatine are made in the same way as in III.4.5.1. We realize sizes of gelatine as in the technology n°5, but this time a juice of lemon is replacing the water.

• In the hole made with the straw, put some effervescent powder.

• Serve immediately.

III.4.6.3. Results:The translucent gel sets and gives a slightly acid and lemony taste. This attempt is appreciated by the Chef.

III.4.6.4. Discussion/Interpretation:The taste of the lemon gelatine is pleasant, slightly acid but not intense enough. Also, the effervescent powder reacts once in contact with the gel (Cf. N°10). The effervescence is visible after 4 seconds, and disappears in foam within 2 min. To the taste point of view, the result is satisfactory but not enough to be the main element of a recipe.

III.4.7. Conclusion:The making of "wave guides" with any tasty aqueous solution is feasible by the restaurant team. They can be used as decoration in a dish.

III.5. Baking bars

III.5.1. Objective:Obtain the best baking and the best texture of fish (bar). This fish was cooked with two different manners: under vacuum (at P = –2 bars) or with steam. We looked for a "perfect" (from the Chef point of view) baking of the fish, with ideal temperature and time of cooking.

III.5.2. Material and method:

III.5.2.1. Material:

• 30 g of fish fillet, taken from the dorsal muscular tissue.

• Steam oven, Convotherm OEB precision 2 °C.

• Thermocouple MAFTER K type from –50 to 950 °C; uncertainty of 1 °C, with a needle.

• Plastic bag 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.

III.5.2.2. Method:

1. Cut 30 g of fish into small portions (for an "amuse-bouche").

2. Put these portions in plastic bags under vacuum. (Intensity 4 of the machine).

3. Put them in the oven and measure the temperature inside the fish with a thermocouple (we put the needle in the heart of the flesh).

The first tests were realized under vacuum. The following tests were realized on a plate, where the fish was on a bed of kelp (10 g ± 1 g) with 6 oysters (size of 2 cm). A lid is added and the thermocouple is put inside the flesh of the fish. All is rolled in foil, to keep the environment waterproof.

The different samples were kept in the fridge to compare them in the same time.

III.5.3. Results:The bar placed in the oven at 60 °C under vacuum is cooked at the end of 16 min (exactly), and it can stay in the oven between 15 and 20 minutes. The Chefs cook the fish at 52 °C (inside) for an oven temperature at 60 °C.

III.5.4. Discussion/Interpretation:The Chef prefers the cooked fish fillets when the temperature is between 62 °C and 65 °C, for 15 to 20 min. Below 62 °C, the flesh is too soft, there is a lack of firmness (moreover, for temperatures below 60 °C, there are safety issues). At temperatures higher than 65 °C, the flesh is too firm and dry, according to the Chef.

Also, we can observe the green colour of the algae, which is interesting. The Chef finds some algae savours in the flesh of the bar, and this was what he tried to obtain on the top of its cooking.

From a technical point of view, this method of cooking the fish is easy at the restaurant because the times of cooking are between 15 and 20 min, which corresponds to the interval of time between a command and the service of the dish. The method of cooking is known for the restaurant team. The technique is easy to implement.

III.5.5. Calculation:

III.5.5.1. Fourier's law, statements:Let us consider a volume of material which is at initial temperature T. One of the surfaces of this volume is suddenly heated at a temperature T + ΔT.

III.6. Green tea jellies

III.6.1. Objective:The aim of this study is to get a clear gel from an infusion of green tea (Sencha Silver). The gel has to be dark but not cloudy, neutral (sugar free) and tasty but not astringent.

III.6.1.1. About tea:From a Chinese origin, tea is today the most consumed drink in the world after water.

The tea plant belongs to the genus Camellia (L.) O. Kuntze, of the order of Guttifères, family of Ternstroemiaceae (Theaceae). Kaempfer made the first description in 1712 under the name of Thea Japonense. The Botanical Congress of Amsterdam in 1935 decided to replace Thea by Camellia. So Camellia Sinensis means literally "Chinese camellia" because, indeed, tea plant is a sort of camellia. The kind Camellia counts a little more than 80 species.

III.6.1.2. Tea composition:When tea was introduced in Europe, it was used as a drug. Today numerous scientific studies try to demonstrate the health benefits of this drink, above all with their anti-oxidizing agents. Green teas can be obtained with any plant material. Indeed, this name concerns only the treatment given to the leaves. These processes offer to the leaf the appropriate organoleptic characteristics. The name "green tea" means that the tea isn't fermented. Thus, the enzymatic activity is stopped and replaced by some thermochemical processes.

There are 3 steps of treatment of the tea leaves.

• Roasting: leaves are heated very quickly at high temperature, to stop fermentation.

• Rolling: leaves are rolled or folded. There are so various forms of leaves (sticks, balls, twists).

• Dessication: leaves are finally dried in a warm air.

Contrary to black tea, fermentation and drying of leaves don't occur in green tea. Thus, without enzymatic activity, the contents in tannins, vitamin C, chlorophyll and organic acids don't change significantly after treatment (composition of a leaf of green tea given in the appendix 7; according to "Food Chemistry").

The quantities of the different tea compounds that are present in the drink are dependent on various factors. The main factors are the solubility of these components, the temperature of the water and the time of infusion. In the case of fermented teas, 38 to 40 % of the dry material is soluble in hot water, which is more significant than in the case of roasted coffee. For all the tea varieties, the intensity of the savours is correlated to both the total quantity of polyphenols and the activity of polyphenol oxidases (stopped in the case of green teas).

III.6.2. Gels from infusions of tea.

III.6.2.1. Material:

• Green tea (Sencha Silver).

• Tap water.

• Gelatine and Agar-agar provided by Louis François.

• Carrageenan Kappa (+locust bean gum), IBERAGAR product Ref S-3847 / 04.

• A plastic bowl of 1 L.

III.6.2.2. Method:

1. Make an infusion with 20 g of tea in 1L of water.

2. Filter the solution, and keep the leaves.

3. Split the solution into 5 bowls of 200 g.

4. Repeat the steps 1 to 3 five times, reusing the same tea leaves.

5. Take 3 samples from 3 successive experiments and add some gelatine to form a gel at 1% and keep them in the fridge. We wish to observe the complex formed between tannins (or more generally phenolic) and proteins of gelatine.

6. Take 3 samples from a same infusion and add some agar-agar to form a gel at 1% and keep them in the fridge. We wish to compare the efficiency of the gelatine to the one of the agar-agar.

7. Make gel with kappa carrageenan (also 1%) with 3 samples.

8. Make one master sample with each gelling agent.

9. The other samples are kept aside and will be used for further experiments.

III.6.2.3. Results:The solutions with gelatine get cloudy and do not set well in gel. Other gelling agents give good results.

III.6.2.4. Discussion/Interpretation:III.6.2.4.1. Concerning gelatine:For each of the successive infusions, we obtain a cloudy liquid, that does not jellify. The third sample, which corresponds to the more infused solution, is cloudier than the two others. This may be due to a bigger quantity of tannin.

However, the master sample with gelatine gives a gel that sets. The tannins of the tea may form a complex with the proteins of the gelatine, and this complex gives this cloudy aspect of the solution and prevents from the gel setting.

A first attempt to filter the solution (Tork Premium multipurpose clothes 530 folded.) is unsuccessful. The following steps would be to allow the solution to settle (48 hours), to separate the complex by sedimentation, and to use the solution to make a gel.

III.6.2.4.2. Concerning agar-agar:With solutions of agar-agar at 1 %, the gel sets. It is dark, rigid and breakable. It doesn't give a significant taste and it has an unpleasant consistency.

III.6.2.4.3. The case of the carrageenan kappa:The gel of carrageenan at 1 % set. It is dark, rigid and elastic. It gives a rubbery consistency and doesn't have a pleasant taste.

III.6.2.5. Conclusion:These kinds of tea jellies can't be used in the restaurant. According to the Chefs, they don't have enough taste. However, they can be used in cake baking by making them sweet, to heighten the taste of the tea.

We suggest making a gel with gelatine by trying to remove the complex, responsible for the non-setting of the gel.

III.6.3. Experiments on gelatine.

III.6.3.1. Objectives:The aim of this study is to estimate the influence of the presence of tannins on the setting of the gelatine solutions made of infusion of green tea.

III.6.3.2. Material:The same material as in III.6.2.1. is used.

III.6.3.3. Method:

1. Keep the solutions for 48 hours in a bowl to allow them to settle.

2. Take the solution of the top (100 g are enough), to avoid the tannins.

3. Add some gelatine to make a solution at 1%.

4. Heat the mixture (to homogenize the solution) and then place the solution in the fridge to let set in gel.

5. Make also a master sample at 1 % of gelatine.

III.6.3.4. Results:Using the tea solutions which are settled, the gel sets and its texture looks like a gel made of a solution at 10 g of gelatine per L. Indeed, the firmness looks like a master sample at 1 % more than a master sample at 1.2 %. However, the taste is not pronounced enough and the color is too clear.

To compare, a solution of tea + gelatine at 10 g/L without being settled. In the case of the witness of infusion of Tea + gelatine 10 g/L not settled, the solution becomes slightly confused during the introduction of the gel. A gel formed but we did not eliminate the tannins of the solution!

III.6.3.5. Discussion/Interpretation:The gel made of a settled solution with 1 % of gelatine and homogenization is less firm than the gel made of the floating part of the solution. However, it has the same other characteristics such as a too clear colour, and a not enough pronounced taste. Also, it seems to have some tannin, settling on the bottom of the bowl, and the gel isn't clear.

A hypothesis could be the formation of a complex between tannins and the gelatine. On the whole, the quantity of introduced gelatine was to be sufficient to trap the totality of phenolics of the solution. To introduce for a second time some gelatine allows then to form a gel. In the case of our infusion stemming from the experiment 1, this one was put settling during 72 hours before introduction of the gelatine. Except, the solution taken for the dosage corresponds to the floating because this solution was not homogenized. It would seem that tannins settled in the heart of the bowl, the gel was then able to form.

Finally, the solutions of tea were infused more than half an hour, which is long enough to extract all the sapid molecules and tannins. However, the gel isn't tasty enough. Has the gel any influence on the liberation of savours?

III.6.4. Assessment:

III.6.4.1. Agar-agar and carrageenan gels:The addition of agar-agar induces to darken the colour of the solution of tea. We can't work with this texture, which gives an unpleasant sensation. Playing on different concentrations of agar in solution does not improve the texture and the taste of the gel.

III.6.4.2. Gelatine gels:The colour of the gel is disturbed by the complex, and the gel setting is difficult. The texture is however ideal.

III.6.5. Conclusion:Tea gels are not useful in kitchen according to the Chefs, because they don't give any satisfactory results in terms of taste, even if technically, the preparation of gels is easy.

The flavour depends on the quantity of phenolics present in the solution, but unfortunately, they are not present in the gels of gelatine. However, a last solution brought by Hervé This on Pierre Gagnaire's site concerning jellies of tea, would be to let infuse the tea for a short time to avoid the release of phenolics and then to make a gel with some gelatine.

III.6.6. Other suggestions openings, ideas, applications of the technology:The gels of tea are technically feasible, but the recipe has to be improved in order to use them in a restaurant. An idea is to use a mix of different gelling agents, to take advantage of their different properties.

Is a tea gel a good approach if the tannins can't be used, when they mainly give the taste of tea? Also, the Chef wanted to use the gels of tea in salty and warm dishes. Are there not more interesting alternatives like the pearls of gelatines? (technique number 1).

III.7. Alginate pearls

III.7.1. Objective:We wish to obtain pearls of gel with a liquid heart. These pearls would have the size of a drop.

III.7.2. Introduction:The protocol for making these pearls is used for more than 20 years by the food industry. One easy culinary version is given at www.enfance-nutrition.org, column cook with additives / alginates. This recipe was proposed by Hervé THIS in 1994 and it was shown during one of the Seminars of Molecular Gastronomy by Rachel Edwards-Stuart.

The recipe:

• 100 ml of pear juice.

• 1 g of alginate of sodium: E 401, supplied by Louis François Inc.

• 2 g of calcium chloride mixed in ½ litre of water.

• CaCl₂ in powder in 1 % of water (calcium lactate was also used with good results).

Preparation of the alginate solution:

1. Weigh 1 g of alginate of sodium.

2. Mix with 1 g of caster sugar to facilitate the dissolution.

3. Two techniques can be used:i. Mix 1 g of sugar (or salt) with 1 g of the alginate.ii. Dissolve the alginate in water 1 g in 30 mL of water, cold or at 50 °C.

4. Add drop by drop the alginate to the juice of pear (about 1 to 2 %) and stir until complete dissolution.

5. Prepare a solution of chloride of calcium at 2 %: 10 g of CaCl₂ into ½ liter of water.

6. Immerse a sieve in the solution of chloride of calcium so that we can get back the balls more easily.

7. Fill a syringe with the juice and put the drops in the solution of chloride of calcium: some pearls get formed.

8. Make set the pearls 10 seconds and then rinse them in clear water, to eat them without any risks. The more pearls stay into the solution of chloride of calcium, the more they harden.

III.7.3. Tests with a juice of melon Gaïa:

III.7.3.1. Material:

• A melon.

• Sodium alginate, additive E 401; supplied by Louis François inc.

• CaCl₂ in granules at 1 % of humidity.

• A tub of water, a sieve.

• A syringe.

• A blender: robot GT 550.

III.7.3.2. Method:

1. Make a puree of melon by mixing the flesh with the Blender, during 1 min at speed 5.

2. Make a solution of 1 % of alginate with the juice.

3. Make a solution of CaCl₂ of 1 %.

4. Make some drops and let them fall into the solution of CaCl₂: some pearls get formed.

5. Make set the pearls 10 seconds and then rinse them in clear water, to eat them without any risks.

III.7.3.3. Results:The film of gel is too thick and the taste is unpleasant. Also, the shape of the pearls looks more like tears than balls.

III.7.3.4. Discussion/Interpretation:Here, the solution is constituted by a puree of melon, which thus has some pulp. A new test is then realized with only a juice of melon.

III.7.4. New test with melon juice:

III.7.4.1. Material and method:Same material and method, where the puree of melon is replaced by a juice of melon.

III.7.4.3. Results:We get a better texture and a better shape of the pearls.

III.7.4.4. Discussion/Interpretation:Such pearls can be used in the restaurant without any problem, with any type of juice, it is however necessary to verify the viscosity of this one to obtain the ideal consistency of the pearls. The pearls have the volume of the drops put into the solution of chloride of calcium and they are easier to form when their height of falling is small.

It is interesting to note that these pearls are not feasible with all solutions: for example, a test with a raspberry juice did not work (acidity and calcium content of the initial solution have to be considered carefully).

III.7.5. Theoretical amount of calcium alginate formed by this technique:The calcium chloride gives an unpleasant taste to the pearls, and the rinsing must be carefully realized to avoid a too important quantity of calcium at the surface of the pearls. A rough idea about the quantity of calcium ingested during the consumption of our pearls can be calculated.

Let be a solution made of 1 % in weight of alginate.

M_alginate = 50 – 100 000 g·mol⁻¹.M_Ca²⁺ = 40 g·mol⁻¹.

Hypothesis: 100 balls of 1 cm of diameter are eaten.

V_100balls = 4/3 · π · r³ · 100 = 52.33 cm³m_alginate = 1/100 · m_water = 0.5233 g = 0.5 gn_alginate = m_alginate / M_alginate

Hyp: 1 Ca for 1 alginate unit, then, n_Ca = n_alginate.m_Ca = n_Ca · M_Ca = n_alginate · M_Ca = m_alginate / M_alginate · M_Ca

m_Ca = (4/3 · π · r³ / 100) · (m / M)

So 0.0002 g < m_Ca < 0.4 g of Ca²⁺ is eaten.

Moreover, calcium chloride can be replaced by calcium lactate, with good results and no bitter taste.

III.7.6. Evaluation:This technique is easy to realize and easy to adapt in a restaurant. Its time of realization is short; although it is necessary to realize them shortly before consuming them. We can preserve them in some water before raising them, to avoid drying them out.

III.7.7. Conclusion:This is a simple technique to make pearls giving a caviar texture with the savours of your choice. This technique is however already present in other gourmet restaurants.

III.7.8. Other suggestions openings, ideas, applications of the technology:This technique is already a "classic".

III.8. How to create a mist

III.8.1. Objective:The aim of this study is to produce an effect of mist in a glass. The mist would be induced by a warm white liquid (eggs, cream) poured into a glass cooled with ice cubes.

III.8.2. Introduction:A recipe from "hotel and restaurant" is made with a fried foie gras with a warm duck stock poured into a glass containing an ice cube. The picture shows a thick white smoke. Is this reproducible?

Recipe, for 4:

• 500 ml of duck stock.

• 2 soft-boiled eggs.

• 100 ml of liquid cream, 1 spoon of vinegar.

• 1 red sweet pepper.

• Salt and pepper.

• 4 slices of livers of foie gras of 50 g each.

"Foie gras de canard poêlé, glaçon au vinaigre de sureau et poivron dans une brume de lait de canard."

The day before, prepare ice cubes. For this, mix the sweet red pepper (remove the skin) with the vinegar and 100 ml of duck stock, season. Freeze the cubes in a deep freeze.15 min before serving, make a duck stock, reduce it in half, add the liquid cream and mix it with the soft-boiled eggs, put it in a sauceboat.Fry the foie gras, 1 minute on each side. Absorb the fat in excess using an absorbent paper. Set the foie gras in a plate close to a frozen glass with one ice cube.In front of your dinner guests, pour the boiling milk of duck on the ice cube. The thermal shock will induce a mist which will get free of the glass.

III.8.3. First test:

We first used some water as the liquid poured in the glass, and an ice cube made from tap water and vinegar.

III.8.3.1. Material:

• Tap water.

• A soupspoon of white and neutral vinegar for 100 mL of water.

• Food colouring agent of various colours.

• A large glass.

III.8.3.2. Method:

1. Make ice cubes using tap water, and some ice cubes using tap water and vinegar (a soupspoon of vinegar for 100 ml of tap water). Add some drops of food colouring agent.

2. Put ice cubes in the deep freeze at very low temperature, and place there also glasses.

3. Heat some water with some drops of a different food colouring agent.

4. Put one ice cube in a frozen glass and then, pour the warm water on the top.

5. Look at the created smoke, its consistency, its colour...

III.8.3.3. Results:The quantity of smoke that we can see is small and the created mist looks more like steam than smoke; it has no colour. Also, the smoke doesn't spread along the glass.

III.8.3.4. Discussion/Interpretation:Some smoke gets free during the first 5 seconds, but it clears very fast. The ice cube melts (in several minutes), without making any smoke.

A new test is made, with the same protocol as given by the recipe.