Scientific and technical progress modern production Food Industry made big changes in the methods of thermal processing of culinary products of public catering establishments. Along with traditional surface (conductive) methods of cooking, volumetric methods of heat treatment of products are widely used.
Volumetric heating methods are based on the interaction of the product with an electromagnetic field. Electromagnetic energy from the radiation generator, turning into heat, penetrates the mass of the product to a considerable depth and, in a very short period of time, ensures its heating to a ready-made state.
Surface methods of preparing food products according to technological purpose are classified into cooking, frying, frying and baking, hot water and auxiliary. Cooking equipment includes:
digester boilers, the technological medium of which is water or broth at a temperature of 100°C;
autoclaves in which heat treatment is carried out with steam at a temperature of 135 ... 140 ° C;
steam cookers in which the technological process of cooking is carried out with steam at a temperature of 105 ... 107 ° C;
vacuum devices, the working medium of which is heating steam at a temperature of 140 ... 150 ° C.
The group of frying equipment includes:
frying pans in which the frying operation is carried out in a small amount of fat at a temperature of 180 ... 190 ° C;
deep fryers, in which the frying process takes place in fat at a temperature of 160 ... 190 ° C;
ovens (grills, kebab ovens) that carry out the process of cooking food in hot air at a temperature of 150 ... 300 ° C.
Frying and baking equipment includes: ovens, frying and baking cabinets, in which the technological medium is hot air at a temperature of 150 ... 300 ° C;
steam fryers, the working medium of which is a mixture of hot air and superheated steam at a temperature of 150 ... 300 ° C.
Water heating equipment is represented by boilers and water heaters.
Auxiliary equipment includes food warmers, heating cabinets and racks, thermostats, equipment for food transportation.
Volumetric methods of heat treatment of products are carried out: in microwave cabinets of periodic and continuous operation; ultra-high-frequency method provides a high heating rate of products;
IR devices; infrared heating based on the intense absorption of IR radiation by free water found in products;
EC heating devices; electric contact heating is based on the thermal energy released by current for a certain time when it passes through a product that has a certain active (ohmic) electrical resistance;
induction heating installations; induction heating food products, especially with high humidity, occurs when they are placed in an external alternating magnetic field, in which, according to the law electromagnetic induction Eddy currents (Foucault currents) arise, the lines of which are closed in the thickness of the product, electromagnetic energy is dissipated in its volume, causing heating.
The main advantage of microwaves is the speed of heating food products.
However, this heating method also has disadvantages - the absence of a crust on the surface of the product and, as a rule, the natural color of the raw material.
Positive indicators of IR heating are uniform color and thickness of browning.
However, this method has disadvantages:
not all products can be subjected to IR heating;
at high density the flow of infrared radiation may “burn” the product.
EC heating is used both as an independent type of treatment and in combination with other methods. In particular, it is successfully used in the bakery industry for heating the dough mass when baking bread, in the production of sausages, and when blanching meat products.
Induction method heating has not yet become widespread in catering establishments, but it has significant economic opportunities for successful application in future.
Considering that surface and volumetric methods of heat treatment of food products, along with advantages, also have disadvantages, it is advisable to use them in combination in the production of public catering.
2.6 Equipment for mixing food materials. Varieties. Main parameters and factors influencing their values, example of design.
Mixing Equipment designed to connect two or more components that make up the product being manufactured. Mixing equipment is designed for the production of medicines, powders, cookies, dry mixtures and other multi-component products.
In various branches of the food industry, there is a need for mixing liquid products: for mixing two or more liquids, maintaining a certain technological state of emulsions and suspensions, dissolving or uniformly distributing solid products in a liquid, intensifying thermal processes or chemical reactions, obtaining or maintaining a certain temperature or consistency of liquids, etc.
Mixing of food products is carried out in mixers following types: screw, blade, drum, pneumatic ( compressed air) and combined.
Mixing devices are classified (Fig.):
Rice. Classification of mixing machines
By purpose: for mixing, dissolving, tempering, etc.;
According to the location of the device: vertical, horizontal, inclined, special,
According to the nature of processing of the working medium: mixing simultaneously in the entire volume, in part of the volume and film mixing;
According to the nature of the fluid movement in the apparatus: radial, axial, tangential and mixed;
According to the operating principle: mechanical, pneumatic, ejector, circulation and special;
In relation to thermal processes: with a wall heat exchange surface, with an immersed heat exchange surface and without the use of thermal processes.
For fine grinding and mixing of raw meat, a cutter mixer is used. Lumpy viscous and viscoplastic products (flour, meat, minced meat, curd and cheese mass) are mixed with screws, blades in drum and other mixers. Liquid products (milk, cream, sour cream, etc.) are mixed in containers with paddle, propeller and turbine mixers.
Dough mixing machines are divided into batch and continuous machines.
Periodic machines come with kneading containers (bowls) - stationary and replaceable (rollable), and bowls - stationary, with free and forced rotation.
Based on the intensity of the impact of the working body on the dough, dough mixing machines are divided into three groups:
Conventional low-speed (the working process is not accompanied by heating of the dough);
High-speed (the working process is accompanied by heating the dough by 5...7 °C);
Super-fast (kneading is accompanied by heating of the dough by 10...20 ° C and special water cooling of the chamber body is required).
According to the nature of the movement of the kneading organ, machines with circular, rotational, planetary and complex flat and spatial movement of the kneading organ are distinguished.
Continuous dough mixing machines (Fig.) are divided into the following groups:
Rice. Scheme dough mixing machines periodic action with rolling bowls:
a - machines with an inclined axis of the kneading blade and its translational circular motion;
b-machines with an inclined axis of rotation of the kneading blade, made in the form of a pipe with a spatial configuration;
c - machines with a kneading blade, the working end of which makes a curved flat movement along a closed curve;
r-machine with a kneading blade performing curvilinear spatial movement along a closed curve in the form of an ellipse;
d - machines with a spiral-shaped kneading blade rotating around a vertical axis;
e - machines with a four-fingered kneading blade rotating around a vertical axis and one fixed vertical blade;
g - machines with a horizontal cylindrical or flat blade rotating around a vertical axis;
h - machines with a horizontal blade rotating around a vertical axis and an inclined axis of the bowl.
Single-chamber with a horizontal shaft and T-shaped kneading blades, for example the X-12 machine (Fig. a);
Rice. Schemes of batch mixing machines with stationary bowls:
a - machines with horizontal and inclined cylindrical kneading shafts;
b - machines with paired Z-shaped blades rotating in different directions around a horizontal axis;
c - machines with a hinged Z-shaped kneading blade;
d - machines with a polygonal rotor and a screw turn at the bottom of the container.
Single-shaft with a horizontal shaft, on which trapezoidal flat blades are placed at the beginning of the kneading container, and at the end there is a screw auger enclosed in a cylindrical body, for example, a dough mixing machine of the Khrenov system (Fig. b);
Single-shaft with a horizontal shaft, on which a mixing screw is first placed, and then radial cylindrical blades, for example, the FTK-1000 dough mixing machine (Fig. c);
Single-shaft with a horizontal shaft, at the beginning of which a screw is fixed and then a disk diaphragm and a four-blade plasticizer (Fig. d);
Single-shaft with a horizontal axis of rotation, on which a screw drum with an independent drive is placed in a cylindrical mixing chamber, rectangular kneading blades are fixed to the shaft in the conical chamber, and fixed blades are fixed on its walls (Fig. e);
Twin-shaft with horizontal shafts on which T-shaped kneading blades are fixed (Fig. e);
Twin-shaft with horizontal shafts rotating in different directions and belt blades attached to them, for example the Topos dough mixing machine (Fig. g);
Double-chamber, twin-shaft, on the shafts of which helical blades are attached, forming mixing and kneading zones, and the plasticization zone is equipped with two quadrangular sprockets, for example, RZ-KHTO dough mixing machines (Fig. h);
Two-chamber, two-shaft, which have a separate mixing chamber with a drive, and the kneading chamber with an adjustable drive includes two kneading zones: a kneading zone, equipped with screws, and a plasticization zone, the working body of which is fists (Fig. i);
With a three-bladed rotor, for example, a dough mixing machine of the Prokopenko system (Fig. k);
With a vertical cylindrical rotor, for example, a dough mixing machine RZ-KhTN/1 (Fig. l);
With a disk rotor on which annular protrusions are placed, and the annular protrusions of the housing enter into the gaps between them with a small gap (Fig. m).
Rice. Schemes of continuous dough mixing machines
2.7 Equipment for cooling and freezing food materials. Varieties. Main parameters and factors influencing their values, example of design.
Lesson 73-73. Classification thermal equipment by technological purpose, heat source and methods of its transfer.
Thermal equipment for processing products is classified according to heating method, technological purpose, and heat sources.
By heating method equipment is divided into equipment with direct and indirect heating. Direct heating is the transfer of heat through a dividing wall (stove, boiler). Indirect heating is the transfer of heat through an intermediate medium (steam-water jacket of the boiler).
By technological purpose heating equipment is divided into universal (electric stove) and specialized (coffee maker, bakery cabinet).
Depending on the heat source Thermal equipment is divided into electric, gas, fire and steam.
Thermal devices can also be classified according to the principle of operation - continuous and periodic.
According to the degree of automation, heating equipment is divided into non-automated, which is controlled by a service worker, and automated, where control is carried out. safe work and the heat treatment mode is provided with the help of automation devices of the thermal apparatus.
In public catering establishments, heating equipment can be used both non-sectional and sectional modulated.
Non-sectional equipment – this is equipment that varies in size, design and architectural design. This equipment is intended only for individual installation and working with it, without taking into account blocking with other types of equipment. Non-sectional equipment for its installation requires significant production areas, since maintenance of such equipment is carried out from all sides.
Sectional modulated is called equipment that is produced in the form of separate sections from which various production lines can be assembled. It has uniform dimensions in length, width and height.
All heating devices have an alphanumeric indexing, the first letter of which corresponds to the name of the group to which the heating device belongs, for example, boiler - K, stove - P, cabinet - Ш, etc. the second letter corresponds to the name of the type of equipment: digester - P, continuous actions - N, etc. the third letter corresponds to the name of the coolant: electric - E, gas - G, steam - P. The numbers indicate the parameters of heating equipment, for example KPP-160 - a digester boiler, steam, with a capacity of 160 liters.
Heat sources
Fuel and its composition. Fuel is a complex organic compound that can release a significant amount of thermal energy when burned.
By state of aggregation Fuel is divided into solid, liquid and gaseous. TO solid fuel include firewood, peat, coal and oil shale. Liquid - oil and its products - gasoline, kerosene, fuel oil and heating oil. To gaseous – natural and artificial gas.
The composition of the fuel includes combustible (carbon, hydrogen, sulfur) and non-flammable (nitrogen, ash, moisture) elements. Oxygen is a non-flammable element, but supports the combustion process.
Firewood has a low combustion temperature and is considered a local fuel. Peat is a product of incomplete decomposition of organic substances of plant origin with excess moisture and very little air access.
Coal is a high-calorific fuel, has a high carbon content, low moisture content and a small amount of volatile substances.
Oil shale is a layered rock used as a low-calorie fuel; It is recommended to use them after processing or near mining sites.
The main type of liquid fuel used at P.O.P. is heating oil. Natural combustible and artificial gases are used as gaseous fuels, which are superior in quality to all other types. The advantages of gas are high efficiency, the ability to use automation, and the gas will not pollute the atmosphere. Disadvantages - the gas is poisonous, so improper handling of it leads to accidents.
Electrical heating elements. The operation of electrical equipment is based on conversion electrical energy into thermal with the help of a conductor. This uses the property of conductors to heat up when an electric current passes through them.
Currently, only metal conductors made of nichrome or fechral in the form of a spiral are used in electrothermal devices.
According to their design, electric heaters with metal resistance are divided into three main groups: open, closed (with air access) and hermetically sealed (without air access).
Exposed heating elements are nichrome spirals placed in ceramic beads or laid in grooves ceramic panels. They have an increased danger, therefore P.O.P. are practically not used.
Enclosed heating elements consist of heaters placed in an electrical protective shell, which protects them from mechanical damage. They are used in electric stoves and electric frying pans.
Hermetically sealed tubular heaters (TEHs) have been widely used in electrical equipment used in P.O.P.
The heating element is made in the form of a seamless tube made of carbon steel with an anti-corrosion coating. Inside the tube there is a spiral pressed into the insulation. Heating elements have different configurations depending on the location of their installation and the design of the heating equipment.
Heating elements are durable and versatile. They can be immersed in water (boiler, bain-marie, food kettle), in oil and fat (broiler, deep fryer), and also placed in the air (fry chamber, heating cabinets).
Lesson 75-76. Characteristics of the main heating methods. Security automation. Rules for safe operation.
Safety precautions during the operation of thermal equipment depend on the type of energy carrier, its parameters, as well as the technological purpose.
The safety of thermal equipment must be ensured by the design of the devices, the use of all necessary instrumentation, safety and protective devices, strict compliance with the relevant instructions when operating heating equipment.
Heat treatment of products is the main process in the preparation of the vast majority of dishes. It is performed using special equipment called thermal equipment.
Having professional heating equipment in the kitchen is a guarantee successful work food establishments. Moreover, it doesn’t matter whether it’s a roadside cafe or a fashionable restaurant. High-quality units will ensure uninterrupted service and will allow you to bring to life a lot of culinary masterpieces, thereby maintaining the prestige of the establishment at a high level.
When choosing where to go for lunch or dinner, people are guided by a lot of factors, but the key is undoubtedly the quality of cooking. Solid thermal equipment will allow you to process food products without extra effort and preserve all of them beneficial features and unique taste - and as a result, present the client with an appetizing, aromatic dish.
Classification of thermal equipment
All heating equipment offered by modern manufacturers can be classified according to several criteria:
- Depending on the functionality, distinguish universal And specialized devices. The former can perform completely different technological heat treatment processes. The latter cope exclusively with a narrow range of tasks.
- According to the energy source, devices are divided into electric, gas, steam etc. Electrical samples are rightfully considered the most practical and safe - they are the ones that can most often be found in a professional kitchen. The use of gas units remains relevant. All other solid and liquid fuel devices are more suitable for organizing field and off-site kitchens, catering outlets with non-standard requirements or in non-standard conditions.
- According to the method of heating the product, devices with contact And contactless warming up. In “contact” systems, the product comes into contact with the coolant either directly or through a dividing partition. In “non-contact” ones, a thermal jacket “lies” between the coolant and the product.
- Based on the principle of operation, units are distinguished continuous And periodic actions. Continuous devices allow loading and unloading of the product while the mechanisms continue to operate ( electric frying pans, grill, frying surfaces). Periodic devices require a complete stop, and in some cases a drop in temperature, before unloading finished products(combi ovens, deep fryers).
Types of thermal equipment
Thermal equipment for catering establishments is presented on the market in a wide range and is designed both for preparing individual dishes and for performing a whole range of technological operations.
The most popular “representatives” of thermal kitchen units are:
- slabs;
- digester boilers;
- ovens;
- frying surfaces;
- electric frying pans;
- convection and rotary ovens;
- combi steamers;
- food warmers.
Professional slabs- thermal catering equipment intended for preparing main dishes. They may differ in configuration, number of burners, and installation method.
Digestive boilers- units with a reliable protection system. They can significantly reduce cooking time and save staff labor resources.
Fryers cabinets- devices used for baking, frying and heating various dishes.
Fryers surfaces used for frying meat, vegetables, pancakes, omelettes.
Electric frying pans used for preparing fried and stewed dishes from vegetables, fish and meat. Equipped with the ability to tip over.
Convection And rotary ovens are indispensable when it is necessary to bake culinary products.
Combi steamers- universal equipment that can replace several thermal units at once. With its help you can boil and fry, stew and bake, poach and steam, and reheat.
Marmites serve to maintain the temperature of already prepared dishes.
Many catering outlets use electric boilers.
How to choose the right heating equipment for catering establishments?
When choosing heating units for a restaurant, bar or cafe, you need to pay attention to the following points:
- The equipment must be durable, made of of stainless steel, cast iron. Individual elements housings that are not exposed to heat can be made of high-quality plastic.
- It is extremely important that all parts exposed to intense (multi-factor) influence can be replaced without problems.
- The preferred connection type is electricity or gas.
- Calculation of thermal equipment must be made based on the scale of production. The number of devices and all their parameters (power, productivity) must clearly correspond to the needs and capabilities of the establishment.
- Many equipment models boast additional options. Be sure to pay attention to this - some technological bonuses can be very useful.
Why is it better to buy heating equipment from Petrokhladotekhnika?
Petrokhladotekhnika sells heating equipment from leading domestic and foreign manufacturers. Each piece of equipment we sell is different high quality and reliability. Contact the company's managers and you will receive comprehensive information regarding any model of equipment, as well as the most optimal options equipping your enterprise.
We know very well that depending on how competently they are selected kitchen devices, the efficiency and success of the establishment largely depends, so our recommendations are always honest and professional. We value the trust of every client!
Petrokhladotekhnika specialists will not only help with the choice, but will also install heating equipment, and also provide high-level warranty and post-warranty service.
Units for professional kitchens should not only be strong, durable and functional, but also be as affordable as possible. This is precisely the principle that the Petrokhladotekhnika company adheres to: we offer you only reasonable prices!
The variety of methods for heat treatment of products predetermines a wide range of thermal apparatus. They can be classified according to several different criteria.
According to its functional purpose, heating equipment is classified into universal and specialized. Universal heating devices include kitchen stoves, with which you can carry out various techniques heat treatment. Specialized thermal devices are designed to implement individual methods of heat treatment.
According to technological purpose, specialized heating equipment is classified into cooking, frying, frying and baking, water heating, and auxiliary.
Cooking equipment includes digesters, autoclaves, steamers, and sausage cookers.
The group of frying equipment includes frying pans, deep fryers, grills, and kebab ovens.
Frying and baking equipment includes frying and baking cabinets, steam fryers.
Water heating equipment is represented by boilers and water heaters.
Auxiliary equipment includes food warmers, heating cabinets and racks, thermostats, equipment for food transportation.
Depending on the heat source, equipment is classified into electric, steam, gas (solid or liquid fired) thermal apparatus.
But according to the structure of the operating cycle, thermal equipment is divided into periodic and continuous apparatus.
Based on the heating method, a distinction is made between contact heating devices and devices with direct heating of food products.
In contact heating devices, the product is heated by direct contact with the coolant (for example, with steam in steam cookers).
In devices with direct heating, heat is transferred to the products through a dividing wall (for example, boilers and frying pans), in devices with indirect heating through an intermediate coolant. Water, steam, mineral oils, organic and organosilicon liquids are used as an intermediate coolant.
By constructive solution Heat devices are classified into sectional and non-sectional, unmodulated and modulated.
Non-sectional heating devices have different dimensions, design: their parts and assemblies are not unified and they are installed individually, without taking into account interlocking with other devices.
Non-sectional equipment requires significant space for its installation, since its installation and maintenance are carried out from all sides.
Sectional equipment is made in the form of sections in which the main components and parts are unified. The service front for such devices is on the one hand, making it possible to connect individual sections and obtain a block of devices of the required power and performance.
The design of modular devices is based on a single size - a module. In this case, the width (depth) and height are up to work surface All devices are the same, and the length is a multiple of the module. The main parts and components of these devices are as unified as possible.
The domestic industry produces sectional modulated equipment with a module of 200 ± 10 mm. The width of the equipment is 840 mm, and the height to the working surface is 850 ± 10 mm, which corresponds to the basic average anthropometric data.
Sectional modulated equipment has a number of advantages over non-modulated equipment:
The identical width and height of the individual sections allow them to be installed in production lines;
The use of the linear arrangement principle allows saving 12-20% of production space.
Ensures consistency technological process, convenient interrelation of its individual stages;
Unproductive staff space is reduced, which helps to increase labor productivity;
Costs for installation and repair of equipment are reduced;
Reduced costs for laying pipelines, sewer pipes, electrical cable.
To streamline the design and production of devices of new designs, ensure maximum unification of components and parts, and reduce operating costs, all thermal devices have been developed according to GOST standards.
The initial parameters in the standard-size range of heating appliances are: for stoves and frying pans - frying surface area, m 2 ; for boilers - hourly productivity, dm 3 / h; for boilers - capacity of the cooking vessel, dm 3, etc.
Devices operating on electricity, gas, steam, solid and liquid fuels are included in one parametric series, which consists of several types operating on the same type of energy carrier. Devices of the same type can be represented by one or more standard sizes.
In accordance with the GOST classification scheme, the indexation of thermal equipment was adopted, which provides information about the purpose of the thermal apparatus, its energy carrier, size and design features.
Indexing is based on the alphanumeric designation of equipment.
The first letter corresponds to the name of the group to which this device belongs, for example, stoves - I, boilers - K, cabinets - Ш, etc.
The second letter corresponds to the name of the type of equipment, for example: sectional - C, digestive - P, continuous - N.
The third letter corresponds to the name of the energy carrier, for example: steam - P, gas - G, electric - E, solid fuel - T.
A figure distant from letter designation with a hyphen, corresponds to the standard size or main parameter of this equipment: frying surface area, number of burners, number of ovens, boiling water capacity, boiler capacity.
In sectional indexing modular equipment the fourth letter M is introduced - modular KPE-60 - electric digester boiler, with a capacity of 60 dm 3.
KNE-25 - continuous boiler, capacity 25 dm 3 /h, etc.
Control questions:
1. What methods of thermal processing of food products take place in catering establishments?
2. How are volumetric heat treatment methods classified?
3. What is a combined method of cooking food?
4. What determines the duration of the technological process depending on the method of heat treatment?
6. Classification of thermal equipment?
Study on your own:
1. Study the design and operating principle of the “Novy” apparatus for passaging using a combined method.
2. Study the design and operating principle of the apparatus for combined baking of vegetables and fruits.
COOLANTS
Create a uniform temperature field on frying surfaces and in the working volumes of devices can be done in various ways. Easiest to practical implementation indirect heating method, which requires intermediate coolants, i.e. a medium that transfers heat and provides “soft” heating of food products in the apparatus. Classification of coolants that have been used or can be used in heating apparatus for public catering:
Water: steam tables, thermostats
Water steam: autoclaves, boilers, steam ovens
Organic liquids: glycerin, ethylene glycol pans, cabinets, food warmers, boilers, autoclaves.
Diarylmethanes: dicumylmethane (DCM), ditolicmethane - cooking and frying lines.
Organosilicon liquids - PFMS-4, PFMS-5, FM-6, flue gases: frying pans, cabinets, food warmers, boilers, autoclaves.
Humid air: bakery cabinets.
Requirements for coolants.
From the point of view of technical and economic feasibility of use, intermediate coolants must have: high heat of vaporization, low viscosity, high temperatures at low pressures and the ability to regulate them, the necessary heat resistance, low cost, and corrosion resistance. Any coolant can be in three states: solid, liquid, gaseous.
However, it can work as a coolant either in a single-phase state (liquid) or in a two-phase state (vapor-liquid).
Single-phase coolants include mineral oils, which are in working condition at temperatures below boiling points.
Two-phase coolants (water vapor, ditolicmethane) are simultaneously in the vapor-liquid state during operation.
Water.
Water is used in thermal processes as a coolant (heating medium) for direct heating of food products (cooking), as an intermediate coolant in heating jackets of devices operating in single- and two-phase states.
Hot water as a coolant is used mainly in devices to maintain finished products in a hot state. But compared to wet saturated steam hot water has a number of disadvantages: a lower heat transfer coefficient, an uneven temperature field along the heat exchange surface, high thermal inertia of the apparatus, which makes it difficult to regulate the thermal regime of the heated medium.
Water vapor
Steam is one of the most widely used coolants. Its main advantages include: high coefficient heat transfer from condensing steam to the wall of the heat exchanger, constancy of the condensation temperature, the ability to fairly accurately maintain the heating temperature, and also, if necessary, regulate it by changing the steam pressure.
The main disadvantage of water vapor is the significant increase in pressure with increasing temperature. Therefore, saturated water steam is used for heating processes only to moderate temperatures (150°C).
However, the use of water steam in relatively small thermal apparatus intended for POP leads to a significant increase in their metal consumption (due to an increase in steam pressure). In addition, the organization of a boiler facility is required, including steam boilers, a variety of auxiliary equipment (pumping unit, draft devices, chemical water treatment devices, etc.). If such an arrangement is justified for relatively large volumes of steam consumption at food industry enterprises, then for small thermal apparatus for public catering with steam consumption volumes of up to 0.5 t/h, its organization is impractical.
Organic liquids.
Organic high-temperature coolants diarylmethanes, as well as a diphenyl mixture, operate efficiently and stably in a two-phase state, since they are insulators with an almost constant value of physical constants. They have high boiling points and relatively low solidification temperatures. Coolants at temperatures up to 350 0 C do not have a corrosive effect on metals. When heating heating surfaces with a two-phase coolant at atmospheric pressure there is no need to regulate its volume, since during boiling the temperature remains constant throughout the entire volume occupied by both phases. The use of coolants in a two-phase state significantly reduces the amount of liquid poured into the heating chambers, which saves fuel, gas, electricity and reduces heating time. When using high-temperature organic coolants, heating chambers must be sealed to protect the environment.
As intermediate coolant mineral oils are used. Fryers use vapor - T. It is a viscous liquid, odorless, dark brown in color. Vapor - T is used at temperatures up to 280°C. It should be noted that when high temperatures As the viscosity of mineral oils increases, thermal decomposition is observed, which is accompanied by the formation of a film on the surface and impairs heat transfer. In addition, oil vapors burn intensely and explode, which requires their use only in a single-phase liquid state. When designing heating devices using mineral oil as a coolant, it is necessary to take into account that in order to ensure high temperatures in the working volumes of the devices, the heating chambers must be filled throughout the entire volume in order to ensure almost full coverage the entire surface of the working elements. To the disadvantages mineral oils low thermal conductivity must be taken into account, which, with high oil viscosity, leads to prolonged heating. Due to the high inertia of oils, when used as an intermediate coolant, the regulation of the technological process causes certain difficulties.
Basics of Cooking Foods
Classification of thermal devices and their structure
Heat sources and coolants
Heat generating devices
Cooking thermal equipment
Frying heat devices
Operation of thermal equipment
1. Basics of thermal processing of food products
Heat treatment changes the structural-mechanical, physico-chemical and organoleptic properties of the product, which determine the degree of culinary readiness. Heating causes changes in proteins, fats, carbohydrates, vitamins and minerals in the product.
The main methods of thermal processing of food products are boiling and frying, used both as independent processes and in various combinations. Each technique has several varieties (steam cooking, deep frying, etc.). To implement these techniques in thermal equipment, use various ways heating products: surface, volumetric, combined. With all methods of heating food products, external heat exchange is accompanied by mass transfer, as a result of which part of the moisture in the food passes into the external environment. When cooking products in liquid media, some of the dry substances are also lost along with moisture.
Almost all food products are capillary-porous bodies, in the capillaries of which liquid is held by surface tension forces. When foods are heated, this liquid begins to migrate (move) from heated layers to colder ones.
When frying food, moisture from the surface layers partially evaporates and partially moves deeper to colder areas, which leads to the formation of a dry crust in which thermal decomposition of organic substances occurs (at temperatures above 100 ° C). The faster the surface heats up, the more intense the transfer of heat and moisture occurs and the faster a surface crust forms.
Surface heating of the product is carried out by thermal conductivity and convection when heat is supplied to the center of the product through its outer surface. In this case, heating the central part of the product and bringing it to culinary readiness occurs mainly due to thermal conductivity.
The intensity of heat transfer depends on the geometric shape, size and physical parameters of the product being processed, the mode of movement (product and environment), temperature and physical parameters of the heating medium. The duration of the cooking process during surface heating is due to the low thermal conductivity of most food products.
The volumetric method of supplying heat to the processed product is implemented in devices with infrared (IR), microwave, electric contact (EC) and induction heating.
Infrared radiation is converted into heat in the volume of the processed product without direct contact between the IR energy source (generator) and the product itself. The carriers of IR energy are electromagnetic oscillations of alternating electromagnetic field arising in the product.
Infrared energy in the processed product is formed during the transition of electrons from one energy levels to others, as well as during vibrational and rotational movements of atoms and molecules. Electron transitions and the movement of atoms and molecules occur at any temperature, but as it increases, the intensity of IR radiation increases.
Microwave heating of food products is carried out by converting the energy of an alternating electromagnetic field of ultra-high frequency into thermal energy, generated throughout the entire volume of the product. The microwave field is capable of penetrating into the processed product to a significant depth and carrying out its volumetric heating regardless of thermal conductivity, i.e. Suitable for products with different humidity levels. High speed and high ratio useful action heating make it one of the most effective ways to cook food.
Microwave heating is called dielectric heating due to the fact that most food products do not conduct electricity well (dielectrics). Its other names - microwave, volumetric - emphasize the short wavelength of the electromagnetic field and the essence of the heat treatment of the product occurring throughout the entire volume.
The effect of heating food products in a microwave field is associated with their dielectric properties, which are determined by the behavior of bound charges in such a field. Displacement of bound charges under the influence of external electric field called polarization. The greatest energy consumption of an external electric field is associated with dipole polarization, which arises as a result of the influence of an electromagnetic field on polar molecules that have their own dipole moment. An example of a polar molecule is a water molecule. In the absence of an external field, the dipole moments of molecules have arbitrary directions. IN electric field Polar molecules are acted upon by forces that tend to rotate them so that the dipole moments of the molecules coincide. The polarization of a dielectric consists in the fact that its dipoles are set in the direction of the electric field.
Electric contact heating provides a rapid increase in the temperature of the product throughout the entire volume to the required value in 15-60 s by passing an electric current through it. The method is used in the food industry for heating dough pieces when baking bread and when blanching meat products. Products subject to heating are located between electrical contacts. Gaps between the surface of the product and the contacts may cause surface burns.
Induction heating is used in modern induction household stoves and in catering establishments. Induction heating of conductive materials, which includes most metals for cookware, occurs when they are placed in an external alternating magnetic field created by an inductor. An inductor installed under the stove floor creates eddy currents that close in the volume of the cookware. The product is processed in a special metal stovetop container, which heats up almost instantly due to the directed action of the electromagnetic field. At the same time, heat loss to the environment is reduced to a minimum, which reduces energy costs for cooking compared to conventional electric stove by 40%. In such heating devices, the slab flooring is usually made of ceramic materials and remains practically cold during heat treatment.
Combined methods of heating food products are sequential or parallel heating of products using several of the known methods in order to reduce heat treatment time, improve the quality of the final product and the efficiency of the technological process. Thus, combined heat treatment of products in a microwave field and infrared rays makes it possible to realize the advantages of both heating methods and obtain products with a crispy crispy crust.