Cook&Chill: the tutorial for development chefs and process technologists

I

ntroduction

The purpose of this chapter is to introduce the head chef of a commercial or social catering operation to innovative technologies for large-scale food production that preserve the original freshness and nutrient composition of raw ingredients and finished products. The various aspects of implementing the innovative Cook&Chill technology make it possible not only to achieve high quality indicators for the finished product and extend its shelf life (up to 22 days) without the use of preservatives but also to provide opportunities for effective management of the product's direct cost, thereby reducing production expenses.

The use of Cook&Chill technology is approved by the sanitary legislation of the EU and the USA. The technology ensures maximum efficiency of the production process, reflected in indicators such as the staff productivity ratio, the turnover ratio of production square meters, the energy saving coefficient, the effective utilization ratio of thermal and refrigeration capacities, among others. Cook&Chill technology can be effectively implemented both in large-scale production facilities and in operations with small production capacity, as integrating it into their technological process will not require significant changes to their production infrastructure, intra-shop logistics, or labor organization systems.

The Cook&Chill technology involves the use of fairly familiar production tools and equipment units, such as vacuum or barrier bags, vacuum packaging machines, convection, combi-steam, or microwave ovens, food boiling kettles of various capacities, and intensive cooling systems of the air blast type (blast chillers) or water immersion type (tumble chillers or turbo-jet chillers). Cook&Chill technology is applied in accordance with the requirements of the HACCP (Hazard Analysis and Critical Control Points) food safety system, which is much stricter and more comprehensive than traditional domestic SanPiN regulations.

The advantages of the Cook&Chill system have long been proven and confirmed by extensive practical experience worldwide. The technology allows for the simultaneous preparation of large quantities of both homogeneous and heterogeneous products, reducing overall cooking time and energy consumption while significantly limiting costs associated with using not-quite-fresh ingredients upon their arrival at the facility and subsequent spoilage.

Cook&Chill also provides a high degree of protection against the subsequent growth of microorganisms (aerobic bacteria, molds, and yeasts) after heat treatment processes at pasteurization temperatures and below.

The use of vacuum bags, non-stick sleeves, and airtight bags based on composite polymer materials not only protects against the penetration of aggressive external environments into the package but also preserves the natural juices and vitamin spectrum of the original product being processed.

 1. Microbiological Hazard. Types and Categories of Pathogenic Organisms in Food

Rapid microbial proliferation poses a significant risk to consumer health. Virtually any product contains certain types of microorganisms. This is related to the raw material sourcing process and product contamination during processing. Microorganisms are present in water, air, on equipment and utensils, and on and within the raw materials themselves. These microorganisms include bacteria, molds, spores, and even viruses, all of which can lead to a deterioration in food quality.

The potential hazard or health benefit of a product fundamentally depends on the quantity and type of microorganisms it contains. The presence of mold or rot acts as a catalyst for accelerating their primary growth rates. However, in some cases, even in the visual absence of product contamination, microorganisms can provoke serious illnesses and physiological disorders. There are many types of harmful microorganisms that can affect food products. The most common and well-known are Salmonella and Staphylococcus, which can cause muscle pain, fever, diarrhea, and other medical complications.

Pathogenic microorganisms are broadly categorized into three groups based on their resistance and adaptability to temperature: psychrophilic, mesophilic, and thermophilic. Their survivability and reproduction rates in varying climatic and temperature conditions define these categories. Psychrophilic microorganisms thrive at temperatures from 10 to 20°C, mesophilic – from 20/25°C to 40/45°C, and thermophilic remain viable at temperatures up to 55/60°C. At their ideal temperature, each category multiplies rapidly and actively. The speed of their reproduction and survival is also influenced by the pH level (acidity) of the product.

For survival, some microorganisms produce "spores," which have greater resistance and can only be destroyed during heat processing if inadequate temperatures or exposure times are applied. Fortunately, modern methods exist today for assessing the microbiological safety of food products to mitigate these hazards, ranging from sourcing consistently fresh ingredients to proper processing under controlled parameters and the evaluation of Critical Control Points (the HACCP methodology).

Summary:

   Psychrophiles thrive at temperatures from 10 to 20 °C.

   Mesophiles thrive at temperatures from 20-25 to 40-45 °C.

   Thermophiles remain viable at temperatures up to 55-65 °C.

The Time Factor

Under ideal conditions, microorganisms can grow and double in quantity every 15-20 minutes.

   After 3 hours, they can reach a quantity of over 200.

   After 6 hours, they can reach a quantity of over 200,000.

   After 9 hours, they can reach a quantity of over 200 million.

   After 12 hours, they can reach a quantity of over 200 billion.

 Stages of Cook&Chill Technology. Equipment Used

Cook&Chill technology consists of several sequential stages: preparation and sanitary processing of products, their vacuum packaging or placement in a polymer sleeve, cooking via various heat treatment methods, intensive (shock) chilling, and finally, regeneration (reheating) after transportation to the point of sale or distribution.

Let's examine each of these stages individually.

Sanitary Processing

The preliminary sanitary processing of food products should occur with minimal contact between human hands and the food. In high-output kitchens, it is recommended to use automated washing and cleaning lines for vegetables, high-power vegetable slicers, and specific modes for deboning, cutting, and trimming meat, utilizing methods like treatment in mild alkaline solutions with massaging. Sanitary processing is required to remove surface microflora from the product before heat treatment and to eliminate potential bacterial load from cross-contamination by personnel. For food served raw to the consumer (vegetables and fruits), such sanitary processing methods are especially effective. For products undergoing further heat treatment, these measures are more preventive in nature.

Vacuum Cooking or Placement in Clipped Sleeves

When pressure is reduced, water boils (forming steam) at a temperature slightly below 100°C. Food contains beneficial but heat-sensitive components, such as certain vitamins and proteins. Vacuum packaging products in polymer bags significantly contributes to preserving all the beneficial properties of the product. During vacuum packaging, oxygen (which may carry contamination) is removed from the package, preventing oxidation reactions (changes in molecular structure) or denaturation (loss of biological value) of many components in the food product.

Consequently, cooking sous vide (under vacuum) allows many of the product's microelements to remain unchanged, both nutritionally (vitamins, proteins, carbohydrates, and fats) and organoleptically (taste and aroma). The vacuum method protects food from organoleptic changes that can occur during traditional heat treatment and exposure to high temperatures, which primarily affect color, smell, taste, weight, and the digestibility of the food product. Furthermore, this practice ensures greater cooking consistency and enhanced hygiene safety during the product's storage period.

Vacuum cooking is applicable to fresh products and semi-finished products placed in packaging that, during the cooking process, prevents the loss of moisture, natural juices, and volatile compounds.

Any food product, depending on its ingredients and molecular structure, undergoes stages of morphological changes based on cooking temperature and duration.

Regardless of the heat treatment method used, cooking temperatures typically range from 65°C to 95°C (at least at geographical altitudes above sea level). Exceptions are methods like vacuum boiling and retort pouch autoclaving.

An important parameter to control whenever possible is the temperature delta—the precision and accuracy of heat transfer. Temperature fluctuations during cooking should not exceed 2°C. Control over and the precision of the cooking temperature regime become primary factors in choosing equipment, which is the foundation of success for any catering enterprise.

The minimum temperature for cooking in a vacuum bag is +70°C, while the maximum is +93/95°C.

Special attention should be paid to the texture and thickness of the product being cooked. Increased product thickness necessitates cooking at lower temperatures; therefore, a product thickness exceeding 5 cm will require an increase in cooking duration. In classical technological literature, a 5 cm thickness limit is recognized as the maximum recommended cut thickness for rapid cooking.

Advantages of Vacuum Bag Cooking:

   Preservation of product aromas and juices.

   Reduction of weight loss by 15-35%.

   Energy savings of 20-28%.

   Prevention of product drying out and dehydration.

   Prevention of lipid oxidation in the product and, consequently, rancidity.

   Longer storage life of the product after vacuum cooking.

   Saving on spice quantities by 3-40%, as the concentration of seasonings and fats is preserved due to the packaging.

   Increased cooking speed while maintaining thermal input efficiency.

Cooking Meat in Vacuum Bags

For cooking red meats (beef, lamb, pork, etc.), cuts such as fillets, thin ribs, and other boneless pieces are used. For white meats, such as chicken or turkey, only breast or tender cuts should be used. This technical requirement is very important because the meat is cooked at low temperatures for relatively short periods; if meat rich in collagen (found in connective and fibrous tissues) is used, there is a risk of the pieces becoming tough after cooking.

Cooking Fish

Cooking fish sous vide or in Modified Atmosphere Packaging (MAP) is particularly beneficial for preserving the product's typical flavor, which is nearly impossible with other heat treatment methods. Moreover, this method is optimal for maintaining aromas and the soft texture of the flesh, avoiding excessive water loss and subsequent loss of nutritional value. Cooking temperatures should be between 70°C and 82-85°C. Using medium temperatures is ideal for preserving the tenderness of lean fish varieties, which do not tolerate high temperatures well. Special attention must be paid to cooking shellfish with shells, as they can open wide during cooking and potentially breach the packaging integrity. In these cases, it is recommended to cook using an inert gas (MAP) inside the package or add a small amount of water to the vacuum bag.

Cooking Products of Plant Origin

Vacuum cooking is ideal for most vegetables. This is due to the preservation of aroma, taste, and color while "softening" the fiber, which represents the main structural component of plants. Cooking vegetables sous vide is recommended at temperatures of 90-92°C for varying durations until their texture becomes soft to the touch.

When cooking vegetables in a vacuum bag or MAP bag, several points should be considered:

   Green vegetables and fruits (spinach, zucchini, etc.) may undergo color changes: they first briefly acquire a more vibrant and intense green color, which may then lose its intensity.

   When cooking vegetables in a vacuum bag, overly ripe vegetables that may quickly become mushy in their own juices should not be used.

 Intensive Blast Chilling in Cook&Chill Technology

Another defining process in Cook&Chill technology is the rapid chilling of products followed by storage.

Rapid chilling is a key aspect of organizing efficient and economical production. In Europe, product chilling processes are regulated by sanitary legislation. Chilling is defined as a process that reduces the temperature at the core of the product from +65°C to +10°C within 2 hours. A product treated this way can be stored in a refrigerator at +2/3°C for up to 6 days and be brought to serving temperature (+65°C and above) within 1 hour before serving.

In the USA, this process is regulated differently. The Cook&Chill process can take place in a tumble chiller system (water immersion cooling using ice) within 1 hour, after which it can be stored at +2 to +4°C for up to 22 days without added preservatives. In this case, the temperature drops from 92°C to 10°C.

It's important to distinguish this from shock freezing. Shock freezing is a process that reduces the temperature at the core of the finished product from +65°C to -18°C within 4 hours. A product treated this way can be stored in a freezer at -20°C for 8-12 months. This technology is not part of the standard Cook&Chill method.

As noted earlier, any product naturally contains a certain amount of bacteria, which, multiplying under favorable conditions, lead to dangerous health effects for the consumer. Fortunately, high temperatures are lethal to most microorganisms, so it is often sufficient to treat the product at an appropriate temperature for a certain time to completely destroy or neutralize them. The goal of any production process is to minimize the chilling time of the finished product to reduce the risk of secondary cross-contamination.

Two main technologies for intensive chilling are used worldwide: blast chilling and tumble/immersion jet chilling. Let's examine each in detail.

Blast Chillers come in two main types: single-cycle chillers, which cool the product to a temperature of 0-2°C, and two-cycle chillers, which can either chill to 0-2°C or freeze to -18°C. The device is equipped with a temperature probe that allows monitoring of the actual product temperature during the chilling cycle. This needle-shaped sensor is inserted into the core of the product to show real-time temperature changes within its thickness, which cools more slowly than the surface.

Blast chilling modes are subdivided into air cooling in "SOFT" and "HARD" modes.

   Air cooling in the "SOFT" cycle quickly lowers the product core temperature to 2-3°C from an air operating temperature of 0-2°C, never dropping below 0°C. This cycle is particularly suitable for small quantities of products with small thickness (i.e., products not exceeding 4-5 cm in diameter) or for "delicate" products like mousses, desserts, certain fish, and plant-based products.

   Air cooling in the "HARD" cycle, in contrast, rapidly reduces the product core temperature to 2-3°C using an operating temperature range from -15°C to 2°C. This cycle allows for temperature reduction over shorter periods. It is used primarily for large quantities of products with significant thickness (more than 5-6 cm) or for products with high fat content, which impedes rapid core cooling. Rapid chilling is mainly performed by single-cycle blast chillers, which set an operating temperature of about -12/-15°C and bring the product to 2-3°C. Using this method, products stored at +4°C can be kept in the refrigerator for several days, up to a maximum of 6-7 days. This shelf life can be almost doubled when using vacuum or MAP packaging.

It is important to note that at very low temperatures (-30/-40°C) and over a short period (< 4 hours), as water transitions from liquid to solid, the product becomes filled with micro-crystals of ice that do not destroy the texture or internal cellular structure of the product. In conventional freezers, freezing periods are typically within 12/15 hours, so freezing occurs more slowly, allowing for the formation of larger ice crystals responsible for product quality degradation. This effect is noticeable during thawing when an abundant release of internal juices from the damaged product structure occurs.

Chilling in blast chillers is carried out in stainless steel GN (Gastronorm) containers. Thanks to the standardization of their sizes (1/1: 53x35 cm or 2/1: 53x65 cm), these gastronorm containers are ideal for both rapid chilling and subsequent use in combi ovens.

Advantages of the Cook&Chill System and Blast Chillers

   Operational Advantage: Ability to store products for up to 5/6 days in a standard refrigerator at a temperature regime of +2°C to +4°C.

   Economic Savings:

       Potential to reduce fixed operational costs by shortening cooking time and labor costs.

       Reduction in the number of cooking cycles (product is heat-treated only once).

       Lower energy consumption.

       Effective use of preserved/pre-prepared components and reduced procurement costs.

   Service Quality:

       Ability to use pre-prepared components in production that cannot be made "à la minute" just before service.

       Possibility to prepare components in advance.

 Thawing. Defrosting.

During the thawing process, product temperature should never exceed +10°C.

A thawed product cannot be refrozen but must be consumed within 24 hours after complete thawing or cooked within 12 hours.

There are four methods for thawing products:

1.  Thawing in a Refrigerator

    This is the recommended system for meat, poultry, and fish. The frozen product, removed from the freezer, is placed in a refrigerator well in advance (6-12 hours before cooking). Thawing always produces water released by the product itself or from frost on the packaging; therefore, a tray to collect water must be placed underneath the product.

2.  Thawing in Water

    Any product can be thawed under running cold water, provided its packaging is sealed and airtight. The time required in this case will be less than 4 hours.

3.  Thawing in a Microwave Oven

    It is also possible to use a microwave oven, but only if the product will be cooked or consumed immediately after thawing.

4.  Thawing in an Industrial Defroster

    The product can be thawed in an industrial microwave, steam, or high-frequency defroster.

Techniques That Must Not Be Used

Thawing must not be performed at room temperature and, especially, in warm water. It is also prohibited to thaw products in water if they are not protected by airtight packaging.

 Regeneration

Cook&Chill technology includes a regeneration (reheating) step before service.

The critical temperature range for bacterial growth is between +10°C and +65°C. Therefore, as prescribed by European regulations, at the moment of service, the core temperature of the product must not be below +65°C.

The use of combi-steam ovens (convection steam ovens) is usually sufficient for regeneration. In the West, regeneration in a regular pot or boiling kettle is also common, where the product is heated in a special multi-layer composite polymer bag, clipped on one or both sides.

A significant advantage of using microwave ovens is the noticeable acceleration of the regeneration process. However, it is important to note that by acting primarily on water molecules, microwaves can soften products, which is not always desirable. Therefore, shortly after microwave treatment, products often benefit from brief finishing in a convection or combi-steam oven.

Low-pressure steam (temperature less than 100°C) is used for regenerating products prepared sous vide. In this case, as with cooking, there is an advantage in enhancing aromas and colors, especially for meat or fish products. Another benefit of this technique is the preservation of nutritional integrity. Starting with individual ingredients cooked sous vide and combined at the moment of regeneration, a wide variety of complex dishes can be assembled.

Tumble chiller technology is not yet widely used in Russia. The company Gastronorm was one of the first in Russia to introduce this technology into the catering industry. The technology is based on packaging products in vacuum bags and special clipped polymer sleeves.

Tumble Chilling System in Cook&Chill Technology

For tumble chilling, special barrier vacuum bags and sleeves made from composite materials of ethylene-vinyl alcohol copolymer, polyamide, and linear polyethylene are used. Such high-quality packaging is not produced in Russia and is imported. The essence of the technology is simple. Pumpable products (non-textural items such as finely-fractionated soups, sauces, stews with small pieces, beverages, etc.) are cooked in an agitator cooker—a specialized boiling kettle with steam injection into various "dead" zones to prevent burning. During cooking, temperature is controlled by a special thermoprobe. Upon reaching doneness, determined by the industrial controller's program, the product is pumped via a pneumatic pump into a multi-layer bag. The product is then placed in an open or closed tumble chiller. The product is treated at pasteurization temperature to reduce bacterial activity and suppress natural enzymes. Subsequent intensive cooling in the tumble chiller occurs up to 14 times faster than in a standard blast chiller. This speed is necessary to prevent some microorganisms from having time to produce spores in the product, which are much more resistant to heat than the aerobic bacteria themselves.

During the packaging and clipping process, a label is applied indicating the product type, weight, batch number, and destination point for transportation. After chilling, the bags are placed in transport trolleys and sent to the central dispatch cold store.

Tumble chilling technology originated from cooled stationary baths where product-filled bags were placed in ice water. Even then, it was noted that this cooling method was incomparably cheaper than blast chilling, despite the costs associated with producing flake ice. The drawbacks of ice bath cooling were the need for a powerful ice generator, a large bath volume, and organizing a closed water circulation system with an external chiller for cooling. The mechanized tumble chiller differed from a simple bath by rotating the bags in its drum, significantly improving heat transfer and accelerating the process. Today, in many US school food service operations (satellite school feeding combines), ice bath cooling technology is still used. Such baths are equipped with lifting mechanisms for unloading baskets of bags. However, this method is now considered less practical and inconvenient for staff.

Western specialists have developed clear criteria for choosing between a blast chiller and a tumble chiller. It is advisable to choose a blast chiller only under the following conditions:

   The dish regeneration time is not longer than its initial cooking time.

   Production of fried products or textural items (cutlets, rolls, etc.).

   Production output is less than 1,500 meals/day.

   Your chilling batch frequency is about once per 90-100 kg of product.

Generally, within the Cook&Chill system, there are two approaches to organizing the process: packaging the product first and then cooking it, or cooking the product first and then packaging it. This choice influences the cooling technology selection.

In the first case, a product like a meat or fish fillet is placed in a horizontal tank and cooked at, for example, +65°C. Rice can also be cooked this way to prevent overcooking. This method is not only more energy-efficient than cooking in a vertical kettle but also safer, as the product is already packaged in gas or vacuum and is not exposed to cross-contamination after extraction. Cooling in this approach is done directly in the tank by circulating ice water from a central chiller. The product temperature after cooling is about +6°C.

According to the second technology, the product is pasteurized in an agitator cooker at +85°C and chilled from four hours to one hour (depending on the tumble chiller's power) in an airtight bag, clipped after pump transfer.

The entire process is controlled by electronics and an integrated HACCP temperature monitoring module. Despite automated control, it is recommended to take temperature samples throughout the process. For this, the thermometer should be calibrated appropriately.

Packaging for the Cook&Chill System

In the USA, there are three standard bag sizes for tumble chilling technology: 1 gallon, 1.5 gallons, and 2 gallons. This is approximately 4, 5, and 7 liters, respectively. Cook&Chill technology involves filling bags manually or using an automatic filling system.

Sometimes, Cook&Chill bags are cooled in a standard washing sink with added ice from a low-power ice generator. Experienced chefs use this technique in fine-dining restaurants to extend the shelf life of sauces and soups.

The system of packaging in multi-layer bags within the Cook&Chill framework has revolutionized not only the restaurant business but also the US school food service system. Since the 1980s, meals for small and remote rural schools have been delivered precisely using the Cook&Chill system. Several portions of a dish can be reheated in a regular pot on a stovetop.

 Equipment for the Cook&Chill System: Low-Output Systems for Corporate Catering and High-Capacity Systems for Food Production Plants

The foundation of any Cook&Chill system is food boiling kettles, which can have up to 15 different agitator variations for various product types. Systems are equipped with additional equipment such as immersion baskets for pasta, loading cranes, steam injection systems, and additional bottom and side mixers.

Pneumatic pump dosing stations ensure product transfer and portioning into polymer sleeves or bags.

After packaging, cooling occurs in a system of compact water immersion baths with a closed water circulation system. Cooling is achieved using an external water chiller. Cooling can also be performed using blast chillers.

More powerful and larger-scale systems are represented by higher-capacity kettles, pump stations, tumble chillers with a cooling capacity of up to 1 ton of product per hour, and low-temperature tanks for cooking textural and large-piece products in vacuum bags.

by Fedor Sokirianskii