Sorting of raw materials and purification of impurities. Scientific support of the process of cleaning raw materials from the outer cover. Equipment for mechanical cleaning of raw materials
Mechanical processing of raw materials. Heat treatment processes.
1. Classification of machining methods and their brief description
2. Application of mechanical processing methods in food technologies
3. Purpose, classification and characteristics of types of heat treatment
4. Characteristics of the main methods of heat treatment and their application in food technology
Terminological dictionary
Splitting up— The process of dividing a solid body into parts by external forces.
Pressing– The process of processing materials under the action of external pressure.
Heat exchange The process of transferring heat from one body to another
Convection- The process of heat distribution as a result of the movement and mixing of particles of a liquid or gas with each other.
Radiation- The process of transferring heat from one body to another by the propagation of electromagnetic waves in space.
Pasteurization- Heat treatment of raw materials, in which the vegetative forms of microorganisms die.
Sterilization– Heat treatment of raw materials at a temperature of more than 100 ° C, at which spore forms of microorganisms die.
1. Classification of machining methods and their brief description
Processing of most food products begins with their mechanical processing. These methods include washing, sorting, inspection, calibration, cleaning, separation, mixing, grinding.
The process in which rotten, broken, irregularly shaped fruits and foreign matter are selected is called Inspection. Inspection is combined with sorting, in which the fruits are divided into fractions according to color and degree of maturity. Inspection is an important technological process that allows you to remove raw materials that are easily spoiled and degrade the quality of the finished product. The inspection is carried out on belt conveyors with adjustable conveyor speed (0.05-0.1 m/s).
One of the progressive methods is electronic sorting, which is carried out taking into account the intensity and shade of the color of the fruits (for example, green, brown and ripe tomatoes).
The process of separating raw materials according to various criteria is often called calibration. Calibration, provides for sorting raw materials by size, allows you to mechanize operations for cleaning, cutting, stuffing vegetables, adjust sterilization modes, reduce the cost of raw materials during cleaning and cutting. Fruits are sized using belt, vibrating, drum, cable, roller, disk, screw, diaphragm and other calibrators, which are sorted by weight or size.
Washing Allows you to remove the remains of the earth, traces of pesticides from the surface of the raw material, reduces the contamination by microorganisms. Depending on the type of raw materials, various types of washing machines are used: flotation, fan, shaking, elevator, drum, vibration and others.
For the separation of raw materials, various methods are used depending on the nature of the process - cleaning, rubbing, pressing, filtering.
cleaning Raw materials are determined by the features of the technological process of its processing. This operation provides preliminary processing of raw materials in order to separate ballast fabrics and facilitate further processing of the manufactured semi-finished product. When cleaning, inedible parts of fruits and vegetables (peel, stalks, seeds, grains, seed nests, etc.) are removed.
Fruits and vegetables are cleaned in various ways, depending on their physical characteristics and the purpose of processing.
Raw materials can be cleaned of impurities on a grain separator with a system of sieves that carry out an oscillatory movement (for example, green peas) peeled mechanically using machines with a grating surface; thermal, in which there is a combined effect of steam and temperature (0.3 - 0.5 MPa, 140-180 ° C) and a 1-2 mm peel layer is removed in washing-cleaning machines by chemical, acting on the surface layer with a solution of hot alkali (respectively 8-12% solution, 90-95°C, 5-6 min.) (for example, for root crops and tubers, pome fruits).
Rubbing The cleaned raw material is a continuation of the cleaning process from those ballast fabrics that cannot be separated during cleaning. In rubbing machines, the separation process is accompanied by a fine grinding of raw materials. This feature distinguishes wiping machines into a separate group, which is characterized by certain design solutions. Wiping machines can be whip and without whip, with a conical and cylindrical mesh drum, with two shaft supports on which the whips are fixed, and cantilever, from the bridge of the pinch and multi-stage.
Processes Pressing They are used for various purposes: to give the product a certain shape and compact it, to separate the liquid phase from the solid. The pressing mode determines the pressure and duration of the process. In this case, the liquid phase moves through the micro product, overcoming the resistance, increases with increasing pressing pressure.
There are periodic and continuous presses. According to the principle of operation of the drive mechanisms that create force during pressing, the presses are divided into mechanical, hydraulic and pneumatic. In some devices, pressing is carried out under the action of centrifugal forces. In turn, mechanical presses are screw, roller, belt, rotary, etc.
For the distribution of liquid and coarse products, various methods are used: chemical (pasting), mechanical (settling, filtration, centrifugation) and electrical.
Mechanical processes require a long time, so this method is ineffective. A common method for separating polydisperse systems is the process Filtration, Based on the retention by porous partitions (filters) of particles suspended in a liquid. Filtration is divided into two types: surface and volumetric.
surface filtration Used to isolate solid particles from a solution, i.e., to separate solid and liquid suspensions. Volumetric Filtration is used to illuminate drinks, remove dust from the air and other media, i.e., to distribute the colloidal, liquid or gaseous phases of colloidal solutions, sols or aerosols.
As filter elements, fabric napkins or fibrous materials are used. The driving force behind the filtration process is the pressure difference above the baffle (or sediment bed and baffle) and below the baffle. The pressure difference is created using vacuum, compressed air pressure, mechanical supply of the suspension, such as a pump. Microporous filter elements are used to separate very small particles from liquids.
ultrafiltration In the food industry, they are widely used to concentrate protein solutions, starch and other macromolecules in the production of products such as juices, milk, whey, egg whites, etc. Ultrafiltration membranes differ from microporous filter elements in that each pore opens to the side low pressure and any small fraction passes through the membrane, while large ones remain on its surface.
Reverse osmosis It is used to remove minerals dissolved in products, for example, to separate salt or sugar from a solution. The driving force behind the process of moving water across a membrane is the difference between the osmotic pressure of the solution and the hydrostatic pressure drop across the membrane. Reverse osmosis membranes are polymer gels that do not have a porous structure. The movement of water and solutes through membranes is carried out as a result of diffusion, and separation occurs because the rate of diffusion of water is several orders of magnitude higher than the rate of diffusion of solutes. Gel filtration It is mainly used for laboratory analysis, less often in industrial conditions, for example, for desalting cheese whey proteins.
Settling is widely used for purification and refining of liquid semi-finished products. settling— These are sedimentation under the action of its own mass of solid particles suspended in a liquid medium.
Stirring— This is a process in which a random distribution of two or more dissimilar materials with different properties is achieved. It is carried out in various ways. The ingredients are placed in a container that rotates or overturns, resulting in mixing. Peremipiuvannya can be carried out in the tank with blades of various designs. The process may be batch or continuous. Mixing of liquid soluble phases is carried out by stirring or shaking, mixing of solid particles in fluid phases - by dispersion, and high-viscosity systems - by kneading. For mixing liquid mixtures, mechanical, pneumatic, flow, hydrodynamic, ultrasonic, cavitation and combined mixers are used.
grindingsolid food product- This is the process of its deformation until the moment of destruction or rupture, for example, grinding cocoa beans, sugar, milk powder or grinding wheat into flour, etc.
Grinding liquid food product It is a dispersion process, for example, in the formation of emulsions or in the formation of droplets from jets during a spray-drying process. Grinding of food raw materials is carried out by crushing, erasing, impact, cutting. Typically, grinding is performed by a combination of forces, such as crushing and abrasion, abrasion and impact.
Depending on the structural and mechanical properties of the product, the appropriate type of grinding is chosen: for vegetable raw materials - abrasion, impact, cutting, for fragile products - crushing, impact. Technological equipment for grinding can be washing and crushing action (roller and disk mills), impact (hammer crushers), slot (homogenizers, hydrodynamic converters) and cutting (cutting machines) action.
characteristic feature cutting machines There is a separation of the product by a cutting tool into particles with certain predetermined dimensions and quality of the cut surface. As a technological operation, cutting can be carried out by moving the cutting tool in the direction normal to the blade or in two mutually perpendicular directions.
coarse grinding— In which food particles become irregularly shaped and particle size requirements are not rigid, are carried out in crushers. Widely used roller, drum and knife crushers.
For implementation fine grinding Raw materials use disintegrators, colloid mills and homogenizers. The main factor providing the effect of grinding in the disintegrator is shock loads. In colloid mills, fine grinding of the product is achieved due to frictional forces. In homogenizers, grinding energy is provided by hydrodynamic friction forces that arise when a product is forced under high pressure through narrow channels.
Homogenization- This is one of the grinding methods, which consists in grinding particles or drops (dispersed phase) while distributing them in a dispersion medium.
2. Application of mechanical processing methods in food technology
Washing Raw materials are often opened by the technological process, but sometimes it occurs after sorting and inspection in order to improve the efficiency of these processes.
In the process of washing, mechanical impurities (earth, sand, etc.) adhering to the raw material are removed, pesticides, and also microorganisms are partially removed.
Washing of raw materials can occur in soft and hard modes. The method is determined by the mechanical properties of the raw material and the degree of contamination. So, for example, for washing tomatoes, cherries, peaches, washing machines are used that provide a soft mode. These are elevator, fan and shaking washing machines, and berries such as strawberries and raspberries, for example, are washed on shaking shower devices. For washing beets, carrots, zucchini, hard-mode washers are used. At the same time, various mechanized devices are used for washing, in which the raw material is soaked with intensive mixing, which creates friction between fruits or tubers, followed by removal of contaminants using water jets coming out of sprayers under high pressure.
Washing machines with a mild mode provide thorough and quick washing, since with a long stay of soft fruits and berries in water, some of the aromatic, extractive substances and dyes are lost.
Sorting food Products carried out with the aim of: firstly, to ensure the separation of low-quality raw materials, impurities, pollution, and secondly, "to ensure the standardization of raw materials, i.e., its distribution by size, weight, and other properties.
Inspectorate Raw materials are called inspection of raw materials with the rejection of specimens unsuitable for processing for one reason or another (bits, moldy, irregular shape, green, etc.). Sometimes inspection is singled out as an independent process, sometimes it is accompanied by fruit sorting by quality, maturity, color. The inspection is carried out on belt or roller conveyors.
When processing in food production, it often becomes necessary to separate a bulk mixture into fractions that differ in certain properties: the shape and size of particles, the rate of deposition in the liquid phase or gaseous medium, electrical or magnetic properties.
For example, in the brewing and distilling industries, the grain supplied for processing is preliminarily cleaned of impurities, and in the flour milling industry, after grinding, the raw materials are separated into bran and flour, etc.
Size separation of granular or ground solids for the purpose of sorting is carried out by sifting through sieves or filtering through filters that pass small particles, but retain larger ones, and the product can be passed sequentially, separating it into fractions, by settling the granules in a liquid or gas.
cleaning Raw materials are one of the heaviest operations in the technological process of food preservation. When cleaning, inedible parts of raw materials are removed - fruit stalks, sepals of berries, grape ridges, pome chambers, peel of some types of raw materials, scales and entrails of fish, bones of meat carcasses. Most of these operations are mechanized. There are, for example, peeling and rib-picking machines, machines for cutting grains from corn cobs, peeling citrus fruits, and others.
The operations of grinding and cleaning raw materials are often combined. The raw material is crushed to give it a certain shape, to better use the volume of the container, to facilitate subsequent processes (for example, roasting, evaporation, pressing). These operations are usually carried out by machine.
To clean pome fruits from the core with simultaneous cutting into slices, removing seed nests, conveyor-type machines are used. Machines peel the fruit, cut into slices, halves and slices. In zucchini, peelings from the stalk are combined with simultaneous cutting into circles.
Most types of fruit and vegetable raw materials are chemically peeled. For this purpose, the fruits are treated in hot solutions of caustic soda of various concentrations. Under the influence of hot alkali, hydrolysis of protopectin takes place, with the help of which the skin is trimmed on the surface of the fruit, soluble pectin is formed, its molecule will undergo further changes under the influence of alkali: saponification, the formation of sodium salts of pectin acids, methyl alcohol, further degradation of the polymer galacturonic acid. The same thing happens with the cells of the skin itself. As a result, the skin separates from the pulp of the fruit and is easily washed off with a stream of water during the next wash. For alkaline peeling of peaches, use 2-3 % Boiling solution of caustic soda, in which the fruits are kept for 1.5 minutes. Root crops are treated with a 2.5-3.0% solution of caustic soda at a temperature of 80-90 ° C for 3 minutes. After alkaline cleaning, the root crops are washed from the skin and alkali in carborundum washing machines with the abrasive surface removed. Used for peeling root crops and graters with an abrasive surface, as well as steam treatment under pressure of 0.2-0.3 MPa for 10-30 s.
The removal of the upper leaves from the onion is carried out on pneumocibules of periodic action. The stalks from fruits and berries can be separated on rollers in a rubber sheath, rotating towards each other.
The choice of grinding method depends on the properties of the processed product. Hard, brittle materials, such as sugar crystals or dry grain, are best crushed by impact or friction, while plastic materials, such as meat, are crushed by cutting (chopping).
grinding Vegetables and fruits are produced in different ways, depending on whether it is necessary to give the raw material a shape (cutting), or grind it into small pieces or particles without worrying about the shape.
Grinding of fruits and vegetables into pieces of a certain size and shape occurs on cutting machines. Raw materials can be cut in the form of bars, cubes, circles, rectangles, etc. Root crops and potatoes, for example, are cut into bars and cubes, zucchini and eggplant - into circles or pieces, cabbage is chopped. These operations are carried out on machines equipped with a system of disc and comb knives. Machines for cutting vegetables in one plane are widely used (shakers, sauteers), as well as machines in which knives are located in two mutually perpendicular planes (for cutting into sticks).
The production of glue and gelatin begins with the preparation of raw materials, followed by the receipt, processing and drying of the glue broth.
The preparation of raw materials consists in sorting and grinding it. When using bone as a raw material, the preparation of the raw material includes degreasing and polishing (cleaning) the bone.
Raw materials are sorted to select batches that are homogeneous in composition and condition. This makes it possible to conduct the production process at the lowest cost and with the highest yield of high quality products. Simultaneously with sorting, the bone is freed from ballast and harmful impurities: iron, rags, wood chips, horns, hooves, wool, stones, etc.
The bone is sorted by anatomical species and cleaned on a sorting belt (speed 7-8 m/min) manually. By the same conveyor, the bone is fed to the crushing machine for crushing. An electro-magnetic separator is installed between the sorting belt and the crushing machine to trap iron.
Soft raw materials (mezdra, tendons, etc.) are sorted according to the degree of freshness, preservation methods, and other characteristics. When sorting, impurities should be carefully selected. It is not allowed to mix raw and boiled bone. Only bone coming from meat processing plants can be sent to production without pre-cleaning.
2.3 Grinding of raw materials
Grind the bone to increase the surface, which contributes to the most complete extraction of fat and glue. The rate of degreasing and degluing processes depends on the degree of bone crushing. When processing crushed bone, the capacity of the apparatus is better used. Thus, the bulk mass of raw sausage bone before crushing (skeleton) is 200-250 kg/m 3 , and after crushing 600-650 kg/m 3 ; bulk weight of table bone before crushing 400-450 kg/m 3 , and after crushing 550-650 kg/m 3 .
The centrifugal impact crusher (Fig. 1) is used to crush bone in the production of gelatin. Crushers are available for primary bone crushing with a rotor diameter of 600 and 800 mm and for repeated bone crushing with a rotor diameter of 400 mm.
The design of the crusher provides for two stages of crushing. The upper and lower fixed removable combs are attached to its body. The rotor rotates from the electric motor through a V-belt transmission. The loading hopper of the crusher has a size of 815x555 mm. The raw material from the funnel enters the crusher, where the rotor with knives rotates. The bone, passing through the gap between the inner surface of the body and the knives, is crushed. The crushed bone is unloaded through the lower opening in the body.
Soft raw materials are crushed for ease of transportation and intensification of all technological processes. Pre-dry raw materials are soaked in water or a weak solution of lime milk, frozen raw materials are thawed in water with a temperature not exceeding 30 ° C (to avoid hydrolysis and dissolution of collagen). Soft raw materials are crushed on mezdrorezka. Pieces of chopped mezdra should be from 30 to 50 mm.
Crushing plant V6-FDA continuous action is used for grinding meat and bone greaves and dry bone-boy with simultaneous transportation of finished products through pipes using a pneumatic conveyor.
It consists of crusher, blower and cyclones with hoppers. The crusher includes a crusher with a feed funnel and a grinder connected by a hopper. The executive body of the crusher is crushing disks. Along the circumference of each disk there are protrusions that capture pieces of raw materials and, with further rotation of the wheel, crush them into smaller pieces. The crusher is driven by an electric motor through a belt drive, closed by a casing. The grinder consists of impellers and casing. Grinding occurs due to impacts of the product on the working surface of the casing.
A dried and fat-free mixture is fed for crushing, consisting of soft raw materials (up to 70%) and bone (up to 30%), at a temperature of 40 "C. After grinding, the finished product is a dry powder without dense lumps that do not crumble when pressed. Particles of the finished product passed through a 3 mm sieve.
Purification of grain raw materials. Grain raw materials supplied to feed mills contain in their mass various kinds of weed impurities of organic and mineral origin, seeds of weed, harmful and poisonous plants, metal-magnetic impurities, etc. Raw materials containing pieces of glass and other dangerous hard-to-separate impurities are of particular danger. The use of such raw materials for the production of animal feed is prohibited.
Grain raw materials are cleaned from large and small impurities at feed mills by passing it through air-sieve separators.
Purification of farinaceous raw materials. Mealy raw materials (bran, flour, etc.) supplied to feed mills from flour and cereal factories may contain random large impurities - pieces of rope, pieces of rags, wood chips, etc. Mealy raw materials from these impurities at feed mills are cleaned on flat sieves with straight-return movement of the sieve frame, cylindrical burats with circular movement. At large feed mills, ZRM screenings are used to clean farinaceous raw materials.
In addition to the machines listed, a two-tier screening machine DPM is used, the flow diagram of which is shown in Figure 111.
The product to be cleaned through the receiving box 1 with the help of metering rolls 2 is sent in two streams to the upper 3 and lower 4 sieves, making rectilinear-return oscillations. The passages through the sieves enter the prefabricated bottoms 5 and 6 and are removed from the machine through windows 7 and 8 and channels 9 and 10.
To separate light impurities from grain and husk films after peeling oats and barley, aspiration columns, aspirators with double blowing are used.
Purification of raw materials from metal-magnetic impurities. Compound feed containing metal-magnetic impurities in excess of the permissible norms is unsuitable for feeding to animals, as it can cause them serious illnesses. Particularly dangerous are particles with sharp cutting edges, the presence of which can cause injury to the digestive organs.
In addition, the presence of metal-magnetic impurities in raw materials can cause damage to machines and mechanisms, as well as cause explosions and fires.
At feed mills, as well as at flour and cereal factories, metal-magnetic impurities are separated using special magnetic barriers, consisting of static horseshoe-shaped magnets and electromagnets.
Places for installation of magnetic fences and the number of magnetic horseshoes in the fences, depending on the type of product being produced and the productivity of the feed mill, are regulated by the Rules for the organization and conduct of the technological process at feed mills.
Magnetic barriers are installed on the lines:
- grain raw materials - after the separator, before crushers;
- mealy raw materials - after the screening machine;
- cake and corn - in front of crushers;
- feed products of food production - after the separator, before crushers;
- peeling oats - in front of the scouring machine;
- preparation of hay - before each hay crusher;
- dosing and mixing - after each dispenser and after the mixer;
- briquetting - in front of the divider;
- granulation - before each press.
In food production, some raw materials (such as potatoes, root vegetables, fish) are cleaned to remove the outer coverings (skins, scales, etc.).
At catering establishments, there are mainly two methods for removing the surface layer from products - mechanical and thermal.
mechanical method used for cleaning root crops and fish. The essence of the cleaning process of vegetables with a mechanical method is to abrade the surface layer (peel) of the tubers on the abrasive surface of the working parts of the machine and remove the particles of the peel with water.
thermal method It has two varieties - steam and fire.
The essence of the steam cleaning method is that during short-term treatment of root crops with live steam at a pressure of 0.4 ... 0.7 MPa, the surface layer of the product is boiled to a depth of 1 ... 1.5 mm, and with a sharp decrease in steam pressure to atmospheric peel cracks and easily peels off as a result of the instantaneous conversion of the moisture of the surface layer of the tuber into steam. Then the thermally treated product is washed with water with the simultaneous mechanical action of rotating brushes, which leads to the removal of the peel and partially cooked layer from the tubers.
Steam potato peeler (Fig. 3) consists of an inclined cylindrical chamber 3, inside which the screw rotates 2. Its shaft is made in the form of a hollow perforated pipe, through which steam is supplied at a pressure of 0.3 ... 0.5 MPa, with a temperature of 140 ... 160 ° C. The product arriving for processing is loaded and unloaded through lock chambers 1 and 4, which ensures the tightness of the working cylindrical chamber 3 in the process of loading and unloading the product. The screw drive is provided with a variator that allows you to change the rotational speed, and, consequently, the duration of product processing. It has been established that the higher the pressure, the less time is required for the processing of raw materials. In a continuous steam potato peeler, the raw material is exposed to the combined effect of steam, pressure drop and mechanical friction when the product is moved by the screw. The auger distributes the tubers evenly, ensuring uniform steaming.
Fig 3. Schemes of a continuous steam potato peeler:
1 - unloading lock chamber; 2 - auger; 3 - working chamber;
4 - loading lock chamber
From the steam potato peeler, the tubers enter the washing machine (piler), where they are cleaned and peeled off.
With the fire cleaning method, tubers in special thermal units are fired for several seconds at a temperature of 1200 ... 1300 ° C, as a result of which the peel is charred and the upper layer of tubers is boiled (0.6 ... 1.5 mm). Then the processed potatoes enter the peeler, where the peel and the partially cooked layer are removed.
The thermal cleaning method is used on production lines for processing potatoes at large catering establishments. Most catering establishments mainly use a mechanical method of cleaning potatoes and root crops, which, along with significant disadvantages of this method (a fairly high percentage of waste, the need for manual post-cleaning - removing eyes), has certain advantages, the main of which are: the obvious simplicity of the process of cleaning root crops with the use of abrasive tools, compact machine design of the process, as well as lower energy and material costs compared to thermal methods of cleaning root crops (no need for steam, fuel and the use of a washer-cleaner).
The mechanical method of cleaning potatoes and root crops is implemented on special technological machines that have a number of modifications in terms of productivity, design and applicability.