Flour - a valuable food product obtained by grinding grains of various crops. View flour is determined by the crop from which it is obtained. What matters most is wheat baking and pasta flour. Flour is the result grinding - a set of processes and operations carried out with grain and intermediate products formed during its grinding.

All grindings are divided into one-time and repeated. Single-use are so named because the grain turns into flour after passing it through a grinding machine (millstones and hammer crushers) once. During one-time grinding, wallpaper flour (without sifting the shells) of the established yield and gray sifted flour are produced with sifting on thick sieves.

In modern flour milling only repeating grinding, in which flour is obtained through several passes through grinding and sorting machines. Successive impacts on the grain provide gradual grinding, in which it is more fragile than the shells, endosperm rather turns into flour. Thus, principle Processing grain into flour consists of repeated selective grinding of the endosperm and sorting of grinding products after each stage with gradual extraction of flour and separation of the shells (bran).

The following are produced varieties wheat baking flour: premium, first, second grade and wallpaper(without sifting the grain shells, the result is simple grinding). The type of flour is determined by the quantitative ratio of the anatomical parts of the grain contained in it. This means that when varietal In grinding, premium flour is produced from the central part of the endosperm of the wheat grain, first-grade flour from the middle, and second-grade flour from the peripheral part.

Depending on the number of flour varieties produced, varietal grindings are single-grade, double-grade and triple-grade. For each grinding and type of flour, a specific exit flour (% by weight of processed grain). There are the following yields of wheat flour: wallpaper - 96%, second grade (single-grade) - 85%, first grade (single-grade) - 72%, two and three grades - 75 and 78%.

Nutritional value and quality requirements for flour

Due to the fact that flour is different varieties isolated from various parts of the grain, it differs in chemical composition, biological value, nutritional value and digestibility. Wallpaper and second-grade flour contains more proteins, fats, fiber, minerals (ash) and vitamins and therefore has a higher biological value. However, the digestibility and energy value of premium and first grade flour is much higher. The average calorie content of high-grade wheat flour is 1372 kJ, or 325 kcal per 100 grams.

The quality of flour of all yields and varieties is standardized and is characterized by a fairly large number of indicators, which are divided into two groups:

1) independent of the yield and type of flour, that is, they impose uniform requirements on flour;

2) standardized differently for flour of different yields and grades.

The most important quality indicators of the first group are:

- Freshness. Fresh flour should have a weak, specific floury odor and a bland taste. All foreign odors and tastes indicate substandard product.

- Crunch. An unacceptable defect, felt when chewing flour and transmitted to the bread, indicates an increased content of mineral impurities and a violation of the grinding technology.

- Humidity. Should not exceed 15%. At higher humidity, flour is poorly stored, easily sours, molds and self-heats; at very low humidity (9-11%) it quickly goes rancid at high storage temperatures.

Infestation pests of grain stocks are not allowed; if any of the pests are detected, the flour is considered non-standard.

- Harmful impurities. Acceptable within strictly defined limits - no more than 0.05%. They are determined in the grain before grinding.

- Metallomagnetic impurities. Their content is allowed to be no more than 3 mg per 1 kg of flour.

Quality indicators of the second group are characterized by the following data:

- Color. The highest grade flour is white with a creamy tint, the first grade is white with a yellowish tint, the second grade is white with a grayish tint, and wallpaper flour is brownish in color, with noticeable particles of grain shells.

- Ash content. For premium flour there is no more than 0.55%, for first grade flour - 0.75%, for second grade flour - 1.25%, for wallpaper flour - 2%.

- Grind size. Determined by sifting flour through sieves of certain numbers. The higher the grade of flour, the more uniform and small particles it consists of.

Grain grinding is carried out at flour mills with different capacities: at factories - up to 500 tons per day, at mini-mills - up to 1 t per hour. Flour mills use extensive varietal grinding schemes with a developed sieve process, while rural mills most often use abbreviated schemes.

Preparing grain for grinding.

To obtain a standardized yield of flour of standard quality, the grain is subjected to cleaning and conditioning.

The preparatory (grain cleaning) department of modern enterprises occupies approximately 1/3 of the entire production area. The grain is cleaned from impurities in separators, triremes, aspirators, extraction of mineral impurities (stones, pebbles, etc.) is carried out in destoners cars. The residual content of weeds should not exceed 0.4%, and grain - 3%.

To separate the embryo, beard, upper layer of fruit shells, remove dust, reduce ash content and contamination with microorganisms, dry grain surface treatment. To do this, it is passed through wallpaper (hard and soft) and brush cars . For these purposes, it can also be carried out wet grain processing by washing it in washing cars.

Mandatory at mills GTO complex(hydrothermal treatment), or conditioning grains For wheat grains with high glassiness and elastic gluten, it is technologically and economically effective cold conditioning, that is, its humidification cold water (18-20 o C) in intensive humidification screws.

Grain with weak gluten can be subjected to hot or high-speed conditioning, moistening it with hot water or steam and heating to 60 o C, then cooling. After moistening, carry out rejuvenation(resting) grain in special silos for 8-24 hours, depending on the initial moisture content and glassiness. These techniques can be repeated.

As a result of conditioning (moistening and dampening), grain moisture increases to 15.5-16%, its structural-mechanical, physical and biochemical properties improve, the endosperm becomes more fragile, and the shells become elastic and durable. In this regard, the grain is better crushed during grinding, the shells are easily separated from the endosperm, forming large bran, energy consumption and wear of mill equipment are reduced by 20-30%, and the yield of flour, especially high grades, is increased by 1.5-2%. Thus, the economic and technological efficiency of grain conditioning is high.

Immediately before grinding, they can carry out formation of grinding mixtures, mixing wheat grains of different qualities. This allows you to stabilize the quality of the grain (total glassiness 50-60%, gluten content 23%) to properly maintain grinding modes and patterns.

Grinding technology.

Grinding starts with tattered a process by which grain is gradually crushed into intermediate products - grains and duns. The process is carried out on roller machines , the working bodies of which are a pair rollers, rotating at different speeds. As a result of different rotation speeds and the corrugated surface of the rollers, the grain and its grinding products passing between them are split and crushed.
Several roller systems are involved in the trenching process.

For separation by size (sorting by size), grains and duns are sent to screening machines - sieving . Each sift is a cabinet divided into several sections, consisting of a set of sieve frames with different sizes of holes and prefabricated bottoms, and equipped with channels for releasing products. After each drainage system, its own sieving screen is installed. The upper siftings, which have not been sifted through the largest sieves, are sent to the next tattered systems for further grinding. Passing through smaller sieves, flour, fine, medium and coarse grains, soft and hard dunst are sorted. Each product, after being sorted by size, is processed according to different schemes.

After sieving, the grains with developed grinding schemes enter the sieve cars , sorting them by quality (quality factor) and size. This process is called enrichment semolina, it allows you to increase the yield of premium flour during varietal grinding. Sieve machines sort products using 2-3 tiers of sieve frames with reciprocating motion and air flow passing through the sieves. Created fluidized a layer of grains in suspension. The highest quality small grains with low ash content (group 1), containing mainly endosperm, have a high density and low windage.

They overcome the resistance of the air flow, are quickly sifted through sieves and sent to roller machines, where they are ground into flour. Grits with shell particles ( splices) have increased windage. They, as a rule, come off the screens and are sent to torn systems for grinding or to roller grinding machines equipped with rollers without grooves. In them there is a process of processing grains with shells, which is called grinding. After this, the ash content of the grains is significantly reduced, which are again sorted before grinding.

After the sieve machines, small-sized, high-quality grains (2-3%) are not ground into flour, but are sent to the finished product warehouse and are called manna cereal.

Sorted grains and duns are ground into flour (with sifting it out) on roller machines with finely grooved or micro-rough rollers. This process is called grinding. For varietal grinding, several grinding systems operate (from 3 to 12). All flour obtained passes through control sieves and enters breakout mill department. The bran is separated from the upper sieves of the last torn and grinding systems or on whipping machines for grinding out the shells.

Storing flour.

Flour is a less stable product during storage than grain. Positive processes occurring during storage include maturation flour - improving its baking properties (improving the colloidal properties of gluten, whitening the flour). Ripening occurs intensively at a temperature of 20-30 o C and almost does not appear at a temperature close to 0 o C.

However, long-term storage at high temperatures contributes to the overripening of flour and the activation of various negative processes in it. Among them, oxidation and decomposition of fat is observed - rancidity flour. The activity of various groups of microorganisms causes souring, molding and even self-heating of flour. It becomes unsuitable for baking and consumption. No less dangerous is the contamination of flour by pests of grain stocks.

To store flour for several months, you need a dry, well-disinfected warehouse, without any odors. Dry flour is placed on wooden trays in stacks up to 6-8 bags high, leaving indentations from the walls and control passages. Bulk storage of flour in silos is also used. To prevent caking flour, at least once a month it is necessary to change the lower and upper bags in the stack and reload the flour from one silo to another.

The lower the temperature in the warehouse, the longer the flour retains its quality. Therefore, the recommended temperature for storing flour should not exceed 8-10 o C. Very low temperatures (about 0 o C) are less acceptable, since this creates the conditions for moisture condensation. The relative air humidity in the storage facility should not exceed 70% to avoid humidification by air water vapor.

Grain grinding should be understood as a technological process consisting of separate operations, in which one strives to most fully extract the endosperm from the grain in the form of flour, or grind the grain into flour with or without selection of bran.

The grinding process is usually depicted graphically in the form of a technological diagram, on which the symbols show the machines, give their technical characteristics, as well as the direction of movement of the products.

The combination of two machines - grinding grain (or parts thereof) with sifting - is usually called a system.

The basic principles of constructing grinding schemes are continuity, direct flow, consistency and parallelism of technological operations (Fig. 1).

The use of specific methods and techniques is dictated, first of all, by the given range of flour, the quality of grain and the availability of equipment.

Each type of grinding is characterized by the assortment and quantity of flour obtained - the yield.

The flour yield is the ratio of the mass of flour obtained to the mass of grain entering the grain cleaning department, expressed as a percentage.

Optimal output of high quality products is achieved as a result of the use of advanced technology and perfect technology.

Depending on the presence in the general technological process of individual stages, built on certain methods and techniques, as well as repeating operations in the production of a given range of products, grinding is classified into one-time (single) and repeated (multiple), which in turn are divided into simple and complex.

The classification of currently used grindings can be proposed in the following form (Fig. 2). It is based on the frequency of grain grinding, the number of individual independent stages in the technological scheme and the degree of complexity of organizing the sieve process, which occupies a special place in flour production technology.

Grindings based on the production of grains, their pre-processing using beneficiation systems, grinding and developed grinding processes are called high-quality grindings (in the literature the names “grain” or “krupchatnye” are also found).

When producing high-quality flour, only the starchy part of the endosperm is finely ground, and the shells and aleurone layer of the grain are sent to bran in the form of large particles. The germ can be isolated as an independent product or also goes into bran. This task of selective grinding of various anatomical parts of the grain forces us to significantly complicate the flour production technology: it is necessary to introduce additional process stages in which the grinding products are separated into fractions based on the quality factor based on the differences in the physicochemical and structural-mechanical properties of the endosperm, shells and germ.

Varietal wheat grinding involves the following processes:

torn - obtaining grains and dunsts (grain-forming);

enrichment of grains and dung on sieve machines;

grinding - grinding of grains and duns;

begging;

formation of flour varieties and its control.

Varietal grinding, depending on the degree of sorting and enrichment, can be carried out using more or less complex technological process schemes. Depending on the grouping of flour flows, varietal grindings are divided into single-grade and multi-grade, as well as simplified and developed.

With simplified grinding - in mini-mills, intermediate products are divided according to quality into a smaller number of separate streams. They are processed only in sifting machines; sometimes a sieve machine is used. The flour is sifted out on relatively thick sieves.

The purpose of the grinding process is to obtain the maximum amount of flour from intermediate products and, in the final systems, to grind out the final products.

With advanced grinding, intermediate products are sorted and sifted especially carefully, and a large number of sieve machines are used for their enrichment.

When processing wheat, the complexity of the technological process is determined by the type of grinding, which is associated with the established range of flour. When producing second-grade flour, the grinding process can be simplified, the sieve process can be sharply reduced by subjecting only part of the grains to enrichment, and there is no need for a grinding process. This grinding is the main representative of the second subgroup of complex repeated grindings.

Multi-grade grinding of wheat or single-grade grinding into first-grade flour forces the technological process to be complicated in order to ensure the possibility of more complete isolation of the starchy endosperm and its transformation into flour with the lowest possible content of grain shell particles. In this case, both the technological scheme as a whole and its individual stages, including the sieve and grinding processes, are fully developed. These grinds make up the third subgroup. The grinding process in the grinding scheme is closely interconnected with the sieve process, as a single process of grain enrichment.

Thus, the grinding classification scheme takes into account the specific features of their organization, taking into account the range of flour produced.

In Fig. Figure 3 shows a technological diagram of one of the simplest methods for producing flour, obtained by passing grain once through a millstone or hammer mill. This flour is a mixture of crushed particles of endosperm and shells.

Single-grind flour is of low quality, since the crushed shells along with the endosperm end up in the flour, which gives it a dark color, but does not reduce the nutritional value. Due to the absence of a sifting stage (sorting by size) in this type of grinding, the flour turns out to be extremely heterogeneous in particle size; the shell particles, which, due to their elasticity, are crushed to a lesser extent than the endosperm, stand out especially sharply in size.

In cases where it is necessary to sift out shell particles, the grain crushed in this way is passed through sieving machines (sifter, centrifugal, burat), in which shell particles are separated from the mixture of crushed endosperm and shells - bran, which are sent in a separate stream, and the flour becomes more homogeneous and its quality improves (Fig. 4). In general, the resulting flour has low quality indicators, therefore this type of grinding is used only for the needs of small farms and one should not count on higher quality production and sale of such flour.

Since in this case the flour is produced in one step (at one time), such grinding is called one-time grinding. With one-time grinding, you can also obtain a certain amount of light flour; for this, flour sieves 42/48 PA are placed on the first frame, during millstone grinding, on a sifting machine such as a centrifuge or burat. 45/50PA, 36/40PA and the flour of this stream are separated separately.

Rice. 4. Technological diagram of simple grain grinding in a burr mill:

1 - wallpaper flour; 2 - bran (1-2%)

A more advanced type of grinding, in terms of end results, is repeated grinding using roller machines.

Rice. 5. Technological diagram of simple grinding of grain into wallpaper flour on a roller mill:

1 - flour; 2 - bran (2-3%)

In Fig. Figure 5 shows a technological scheme for processing grain into flour, which differs from the previous one in the gradual grinding of grain in several sequential systems. On each system, flour is sifted out of the grinding products, and larger particles are transferred to the next grinding system, and so on until all grain particles are crushed into flour of the required size.

All grinding of grain into flour belongs to the repeating class, in which the grinding operations are repeated.

Simple repeat grinding schemes consist of a single process step in which large particles undergo sequential grinding operations on three to four systems (Fig. 6). Flour obtained from all systems is mixed and combined into one grade. This method produces wallpaper flour from wheat and rye. When grinding rye, another system is sometimes added (Fig. 7).

Rice. 6. Technological diagram of simple repeated grinding

Wallpaper flour is extracted from grinding products on all systems by passing sieves with holes of 0.63-0.8 mm or on nylon sieves No. 8-12. The discharge from the last sorting system should not exceed 3% of the mass of grain supplied for grinding. If additional grinding is required, this collection can be returned to the last system. In all cases of organizing a wallpaper grinding scheme, each system maintains a low grinding mode, i.e. intensive grinding of grain and semi-products.

Technical characteristics of grinding systems for simple grinding are given in table. 1, and approximate grinding modes are in table. 2.

Table 1 Technical characteristics of grinding systems for simple grinding of rye

The technical characteristics of the system are selected in such a way as to ensure intensive grinding of products into flour. Large grooves are cut at a large slope, with a small tip angle, and the rollers are set in the tip-to-tip position. The peripheral speed can be increased to 8 m/s, with a speed ratio of 2.5. To increase the grinding area, it is recommended to use rollers with a diameter of 300 mm.

With those indicated in the table. 2 grinding modes achieve flour extraction of 96% in three passes.

During the control sifting of flour, the same large-number metal woven sieves are installed on the sifter; the sifting material is returned for grinding to system III or IV, if the latter is present in the scheme.

Repeated grinding can be carried out in various ways - simple, which results in flour with a high content of grain shell particles, and complex, in which finer flour is produced, with a lower content of grain shell particles, i.e. best quality.

The problem of obtaining high-quality flour is solved by using complicated repetitive operations (Fig. 8).

As shown in Fig. 9, along with the gradual grinding of grain and sifting on each flour system, on the first few systems, grains and duns are separated, which, depending on the size and quality, i.e. depending on the presence of shell particles (bran) on them, they are grouped into separate streams. These streams are so-called intermediate streams, which, when milled, produce flour of varying quality. It can be combined into one variety or divided into several varieties of a certain quality. In addition to flour, the final result is particles of grain shells - bran. This method produces peeled and sifted rye flour.

Rice. 8. Structural diagram of complex repeated grinding of wheat with a developed process of grain enrichment

Rice. 9. Schematic flow diagram of single-grade grinding of wheat or rye in a low-capacity mill

Peeled flour must meet the following size requirements: residue on sieve No. 045 no more than 2%, passage of sieve No. 38 no less than 60%. The selection of flour for sifting is carried out on fairly rare sieves - No. 23-29, and only on the IV tear and subsequent systems No. 35 is used. Control sifting of flour is carried out on sieves No. 23-29. The ash content of peeled flour is limited to 1.45%, with a yield of 87%. The sieves are thickened on the last systems, on which the product with a high content of shells is crushed. On the same systems, the rollers are installed in the “back to back” position. On the rollers of torn systems, from 5 to 9 corrugations per 1 cm are cut during the process. On grinding systems, 9-10 grooves are used. This scheme is suitable for mills with a capacity of 20-25 tons of grain per day.

When selecting two types of flour from sifting (seeded and peeled), sieves are first installed to obtain the first and then the second quality flour (Fig. 10). For example, for sifted flour, sieve No. 43 and peeled flour No. 26. At control sievings, whitefish are accepted by 1-2 numbers less often than in systems.

The sifted flour should be less ash (not higher than 0.75%) and more dispersed (passage of silk sieve No. 38 is not less than 90%).

The amount of selected shells in the form of bran is much higher and amounts to about 37% when producing sifted and peeled flour. Thus, when producing seeded and peeled flour, the degree of selective grinding is manifested to a greater extent than when producing peeled flour with a yield of 87%.
According to the method of grinding the grain, the described grinding should be classified as repeated, and according to the type - to varietal, since as a result it produces varietal flour.

When processing rye, there is no enrichment and polishing process, since the anatomical features of the grain do not allow obtaining pure endosperm in the form of grains. Therefore, grinding rye into high-quality flour (peeled and sifted) forms the first subgroup of complex repeated grindings.

At the AVM-ZM mill, the torn process consists of four systems. From the first two torn systems, the lower discharge of the sieving sections selects grains, which are ground into flour on the first two grinding systems; in this case, the exit from the sieving of the second grinding system returns to the torn process. If you have another roller mill, you can add another grinding system.

According to this scheme, you can grind single-grade wheat into 1st grade flour with a yield of about 72% or into 2nd grade flour with a yield of 80%. This scheme also allows for two-grade grinding with a yield of 1st grade flour in the amount of 25-34% and 2nd grade - 40-43%.

The numbering of sieves in sieves depends on the selected grinding option. The same applies to the technical characteristics of the rollers (Table 3)

Thanks to the above schematic diagram, we are very close to explaining the technology for producing graded flour on a mini-mill with six or more pairs of rollers. In Fig. 11, 12 show a more complex method of flour production, used in cases where high-quality flour with better quality indicators is achieved.

Here we highlight a process in which we strive to obtain the maximum amount of grains freed from the shells and the minimum amount of flour.

The process is divided into two stages. In the first stage, intermediate products are selected - grains and duns. To improve the quality of the grains, they are sent to sieve machines, where, freed from shell particles, they become cleaner, or, as they say, “richer”, better quality. The products remaining after separating the grains are passed through systems called grinders. This is the second stage of the tearing process, during which the remaining endosperm is removed from the shells (this stage is not shown in the figures).

Some of the most valuable grains, on the surface of which the torn shells are preserved, are passed through roller machines.

The enrichment process includes grinding systems, the purpose of which is to partially grind large grains to obtain a mixture that is more uniform in size, and also to destroy grains consisting of endosperm fused with the shell.

Rice. 11. Technological diagram of two-grade wheat grinding on a three-roll mill

Under gentle pressure from the rollers, the grains split, resulting in smaller but clean grains and particles with shells. This processing of grains is called grain grinding.

The grains, subjected to enrichment and grinding, are fed to grinding systems, where they are converted into high-quality flour in one or several passes.

Rice. 12. Technological diagram of two-grade wheat grinding on a four-mill mill

The remaining intermediate products in the form of grains and duns of the 2nd quality are sent to other grinding systems.

The flour obtained from various torn, grinding and grinding systems, depending on its quality, is combined into grades, and then, after controlling the flour in sifting, they are sent to bunkers of the appropriate grade, then into bags.

The type of grinding is characterized by the yield of flour, by-products and waste.

During baking wheat grinding, the total yield of high-quality flour, including premium and first grades, is 73 ... 78%. With single-grade grinding to obtain second-grade flour, its yield increases to 85%. In addition to flour, 0.7% of waste is obtained III category, 19.1% bran (with 85% grinding - only 12.1%), the rest is feed flour (if the total flour yield is less than 78%).

Grindings are divided into three-, two- and one-grade. The yield of individual flour varieties depends on the equipment of the enterprise, the quality of the grain, market conditions, etc. Usually, when the yield of high-grade flour decreases, the overall yield of flour increases.

When carrying out pasta grinding, the total yield of flour is 75%, including the highest grade - up to 60%.

When grinding wheat into wallpaper flour, its yield is 96%, bran - 1.0, waste III categories - 0.7, categories 1 and 2 - 2.0, shrinkage - 0.3%.

When grinding rye, you get either 87% peeled flour, or 63 seeded, or 15% seeded and 65% peeled; waste III categories and shrinkage make up 1%, categories 1 and 2 - 2.4%, the rest is bran.

Rye wallpaper flour is produced with a yield of 95%, while 2% of bran is obtained, the remaining products have the same yield as in the production of wheat wallpaper flour.

Wheat and rye are ground into both wallpaper and varietal flour, which is why such processes are called wallpaper and varietal milling.

When producing wallpaper flour, the grain is ground almost completely, so the task of the process is to grind it to the required size.

When varietal grinding, it is necessary not only to grind the grain to the required size, but also to separate, to a greater or lesser extent, the shells in the form of bran. In this case, the process is much more complicated and is associated not only with the production of flour on each grinding system, but also with the formation of intermediate products, which, after appropriate processing, are ground into flour with a low content of shells.

Before considering technological schemes for processing grain into flour, let's get acquainted with the concept of "process system" or simply "system".

A system is understood as a separate machine or a set of machines that perform a specific operation. As a rule, a roller machine does not perform the function of a system independently, but together with a sifting machine (sifter or other machine) on which the resulting grinding products are sifted.

The sieving and sieve can independently act as a system. Each system in the technological scheme must have a technical characteristic, examples of which are shown in Figure 1.19, in addition, indicate the number of machines (or machine sections) and the direction of movement of products.

Grinding wheat and rye into wallpaper flour. Wallpaper flour made from wheat and rye is almost whole grain. It is obtained by passing through a metal woven sieve NQ 067.

The technology for the production of wallpaper flour consists of grinding the grain, sifting out the flour and then grinding the waste products until they are almost completely crushed into flour.

The technological scheme for grinding grain into wallpaper flour includes three or four systems, called torn systems, consisting of roller machines and sieves (Fig. 1.19). The main task of each system is the maximum extraction of FLOUR containing both endosperm and shell particles. Therefore, the grooves on the rollers are cut with a large slope and set to the “ edge to edge."

Sometimes the following technological method is used: the products after the roller machine are sent to whipping machines, in which they are divided into two approximately equal fractions. Large products (discharge from the whipping machines) are sent to the next torn system, and smaller products (passage) are sent to sieving; At the same time, the load on sifting is significantly reduced, and the sorting process is shortened.

Since flour predominates in the grinding products, sieves with technological scheme NQ 3 or 4 are used for sifting them, the latter being a modification of the NQ 3 scheme. All sieves in sifters are designed for sifting flour, and metal woven meshes are usually used as they are stronger and more durable. Since in the first systems, mainly the endosperm is crushed into relatively small particles, which are concentrated as a result of self-sorting in the lower layers of the product, for better sifting, the first sieves are somewhat rarefied, and the lower sieves are used more frequently. On subsequent systems that process more bran products, the sieves are thickened. With wallpaper grinding, almost all the grain must be ground into flour. The selection of shells in the form of bran (up to 1% when grinding wheat and up to 2% for rye) is mainly due to the inexpediency of energy expenditure for their grinding, and not only the shells of the main grain are released with bran, but also difficult-to-grind films of oats, wild oats, barley, etc. d.

Flour obtained from different systems is not the same in quality: from the first system to the last, the content of shells in the flour increases.

All resulting flour streams are combined into one and sent for sifting into a control sift, in which large particles that accidentally entered the flour as a result of litter, damage to sieves on individual systems, as well as additional mixing and leveling of the flour composition are separated. Control sifting of flour is usually called “flour control”.

The operating mode of roller machines is determined by the flour extraction rate on each system, i.e., by the number of passes through the NQ 067 sieve. The operation of the systems is considered normal if at least 40 ... 50% of the flour is extracted on 1 torn system, on 11 - 50 ... 70%. The operating mode of the remaining systems should ensure complete grinding of products into flour.

Varietal wheat grinding. The technology of varietal wheat grinding allows us to produce flour of one, two and three grades. Technological schemes for varietal grinding vary in complexity, and the more they strive to obtain high-grade flour, the more developed the technological scheme is.

The first stage of technology - torn process- intended for obtaining intermediate products and grinding out bran, i.e., removing endosperm residues from shell particles.

In the torn process, as a result of grinding and sifting grain products, 3 or 4 groups of fractions are obtained: by-products (one or two fractions), intermediate products (one or two fractions) and flour. The by-products are sent to the next process system, and the torn bran is obtained from the last system. Intermediate products are sent for grinding or, if two groups of fractions are separated, one group for grinding and the other for enrichment.

As a rule, the first two or three systems produce all types of intermediate products, including coarse grains. On subsequent systems that process by-products with a high content of shells, it is impossible to obtain large fractions of intermediate products of good quality, therefore, on these systems, small grains and dunst are first isolated, and then only dunst.

In addition to intermediate products, flour is also obtained in the torn process.

The quality of all products obtained from the latest systems is low. Next stage - enrichment process intermediate products. All intermediate products or some of them are subjected to enrichment. In the latter case, the largest fractions are usually processed - large grains, medium grains, etc., since they contain the largest number of shell particles. Smaller fractions - dunst, fine grits, containing relatively few shells - are not always enriched.

As a result of enrichment, products of different quality are obtained.

Fractions with a low content of shells are sent for grinding, some of them can be isolated in the form of semolina, and the shell products are returned to the last torn systems.

Some fractions of fortified products contain many aggregates consisting of endosperm and membranes. Most of these shells are separated into grinding process, the essence of which is the careful grinding of grains with a relatively large gap between the rollers. When grinding the product, the endosperm is destroyed first - as it is more fragile, the shells are crushed little and, being the largest fraction of the grinding products, can be easily separated on sieves. In addition, a small amount of flour and intermediate products are obtained, sent for grinding or re-enrichment.

Thus, the intermediate products obtained in the scraping process are enriched and subjected to grinding, which makes it possible to separate a significant part of the shells.

Grinding process- the final stage of flour production.

Relatively pure grain products are crushed using grinding systems. The goal of this process is to produce the largest amount of flour with the minimum amount of hulls.

Varietal rye grinding. The technology for processing rye into high-quality flour - seeded and peeled - has a number of features.

In preparation for grinding, the surface of the grain is thoroughly cleaned in beakers; sometimes special hulling machines of the AI-ZShN brand are used, in which it is possible to separate up to 2 ... 3% of the shells, which ensures the production of higher quality

natural flour. .

The increased plasticity of the rye endosperm due to the significant content of mucous substances does not allow processing grain with a moisture content of more than 14 ... 15%; the duration of cooling during conditioning does not exceed 3. .,6 hours

Grain grinding technology includes only two processes - torn and grinding. The enrichment of intermediate grinding products is not carried out due to its low efficiency, which is due to the high content of aggregates in these products. The endosperm from the shells of rye is more difficult to separate, therefore, in roller machines, riffles, as a rule, are arranged “point to point”. At 63% and 80% grinding on the first grinding systems that process products with a high endosperm content, it is possible to arrange the riffles “back to back”, at 87% grinding on all systems - “point to point”.

The main differences in the technological schemes of these grindings lie in the number of grinding systems. The fewer there are, the greater the amount of flour that needs to be obtained from torn systems, so grinding in the torn process should be more intense (Table 1.9).

1.9. Grinding modes for rusty grindings

An important technological operation in flour production is grain grinding. Grinding grain is the process of turning it into flour. There are one-time and repeated grinding of grain.

In single-grinding, flour is produced by passing the grain through a grinding machine once. Commercial flour is not produced in this way. With repeated grinding, flour is obtained by repeatedly and sequentially passing grain and its parts through grinding machines. Repeated grinding includes the following operations: chopping and grinding grain, sorting the ground product by size and weight of particles, removing shell particles (seeds), and forming commercial grades of flour.

There are two types of regrinding: low (simple, wallpaper) and high (varietal, complex). Low repeated grinding is carried out in low operating mode of the rollers. The grain is crushed using three or four systems in one stage. Flour extracted from all systems is combined (mixed) into one grade. Low repeated grinding produces wheat upholstery, rye upholstery and peeling flour. No seedings are taken from the upholstery flour. When receiving peeling flour, 9% of the seedings are selected.

High (complex, varietal) grain grinding is technologically more complex than low grinding. The flour of these millings is obtained by grinding not the whole grain, but parts of the endosperm; they try to separate the shell, aleurone layer and embryo. Thus, grinding grain into flour is carried out in two stages. At the first stage, the grain is converted into semolina, and they try to get the minimum amount of flour. After sorting, the semolina is sent for grinding. According to the number of types of flour that are obtained simultaneously, high grindings are one-, two- and three-grade. In single-grade grinding, all flour is combined into one commercial grade - 1 or 2.

The yield of 1st grade flour is 72%, 2nd grade – 85%. At 78% flour yield, 55-60% of 1st grade flour and 18-23% - 2nd grade are obtained; at 75%, part of the 1st grade flour reaches 65-70%. Three-grade grinding produces baking flour of the highest, 1st and 2nd grades with a total yield of about 78%. High-grade flour is selected within the range of 10-25%, 1st - 40-45%, 2nd - 13-23%.

Flour is packaged in clean and dry bags of at least category III. The bags are stitched with coarse thread (machine sewing) or strong hemp twine (hand sewing). When sewn by hand, bags must have two ears. Flour is also supplied to stores in bags placed in boxes. Pancake flour can be packed in plywood or plank boxes or in four-layer bags...

Mostly wheat, rye, soy flour, etc. are supplied to trade. Wheat flour. This type of flour is produced in five grades: semolina, premium, 1st, 2nd grade and wallpaper flour. Semolina flour is produced from a mixture of durum and glassy soft wheat. Flour yield 10%. It consists of relatively large homogeneous particles. The color of the flour is cream. Krupchatka is most suitable for making...

The chemical composition of flour depends on the grain from which it is obtained. Since the chemical composition of grain changes depending on the soil, fertilizer, and climatic conditions, the chemical composition of flour is not constant. In addition, different types of flour obtained from the same grain have different compositions. This is explained by the fact that when grinding grains into different...

The quality of flour is judged by organoleptic and physicochemical indicators. The most important organoleptic indicators are smell, taste and color. Smell. Fresh flour has a special pleasant smell. Musty, moldy or any other foreign odor is not allowed in flour. Foreign odors may appear in flour due to various reasons. Thus, a musty and moldy smell indicates poor quality grain, from...

Taste The taste of flour is closely related to its smell. It should be slightly sweet, without a bitter or sour aftertaste. A clearly expressed sweet taste in flour is not allowed, as it indicates that the flour is obtained from sprouted grains. A rancid and sour taste indicates that the flour is not fresh. Flour obtained from wormwood grain has a bitter taste, which...

Grain grinding includes two stages: preparing the grain for grinding and actually grinding the grain.

Preparing grain for grinding involves carrying out the following operations: preparing grinding batches of grain, cleaning it from impurities, removing the shells and germ, conditioning.

Lots of grain arrive at flour mills from different places of growth and have different quality indicators.

Grinding batches of grain are compiled with the aim of improving the quality of the grain of one batch at the expense of another. You can mix whole grain that meets the standard requirements for ash content, glassiness, nature and other indicators, or whole grain and damaged grain. Damaged grain includes sprouted grain, frost-damaged grain, damaged by the turtle bug, etc.

Grain is purified from impurities that differ in size and aerodynamic properties using separators. In this case, the grain mass is cleaned by successively sifting on sieves and blowing it with an ascending air flow, which carries away light impurities. Impurities that are not similar in shape to grain (seeds of cockle, wild oats, etc.) are separated on triremes, the main working parts of which are rotating drums or disks with cells on the surface. Triers on which short impurities are separated are called doll-selection machines. In these machines, small impurities fall into the cells and are thrown onto trays, and the cleaned grain goes out. The grain is cleared of long impurities on triremes, which are called oat selection machines. In these machines, the size of the cells corresponds to the size of the grain, and it falls into the cells, and the impurities flow out.

Cleaning of grain from metal-magnetic impurities is carried out when the grain leaves the separator, before it is processed in beakers and brushes, which are used to clean the surface of the grain. The inner surface of the drum in the sanding machine is emery, and in the brush machine it is metal. Inside the drums, flat whips or brushes are mounted on the shaft, which pick up the grain entering the machines and throw it towards the cylindrical surface. In beakers, dust, beard and partly the germ are removed from the grain. Brush machines polish the surface of the grain, removing dust and particles of torn shells.

Conditioning is carried out during varietal grinding of wheat in order to more completely remove the grain shells during grinding. Air conditioning can be cold or hot.

Cold conditioning is carried out by moistening the grain with water at a temperature of 18-20°C and heated to 35°C, followed by chilling in silos for 12-14 hours. During chilling, the grain shells are saturated with water, their humidity increases, they become more plastic and the connection between them and the endosperm of the grain weakens. This allows them to be separated from each other during the grinding process by sieving, since the shell particles will be larger than the endosperm particles. Cold conditioning is used to process grains containing gluten with low extensibility.

Hot conditioning is carried out in air conditioners by heating moistened grain to 55-60°C, cooling it to 16-20°C and freezing it for 2-6 hours. High-speed conditioning is possible, in which water vapor is used to moisten the grain. Hot conditioning is used to process grains containing weak gluten, since heating the grain mass compacts the proteins and reduces the activity of grain enzymes. The hot conditioning mode is selected taking into account the initial quality of the grain gluten. The weaker the gluten, the more it is necessary to heat the grain mass.

Before grinding, the grain is additionally moistened to increase the moisture content of the shells and to more completely separate them from the endosperm.

Preparing grain for grinding can be shortened or expanded. For varietal grinding of wheat, a detailed scheme is used, which includes the following stages: first separation, cleaning on doll and oat selection machines, first cleaning on beakers, second separation, washing and first conditioning (hot or cold depending on the properties of the grain), second cleaning on washing machines, third separation, second conditioning (cold), third cleaning on brush machines, humidification.

Grain grinding consists of two operations: the actual grinding of grain and sifting of the grinding products.

Grinding can be one-time or repeated.

One-time grinding is carried out in one go. In this case, the grain is completely crushed into flour along with the shells. Such flour is of low quality, has a dark color and is heterogeneous in particle size. To improve the quality of single-grind flour, a certain amount of large shells (bran) is removed from it by sifting. One-time grinding is used quite rarely. They are carried out using hammer crushers.

Repeated grinding is more perfect. The grain is ground into flour by repeatedly passing through grinding machines called rollers. After each grinding, the resulting products are sorted by size in sieving machines called sieves.

The main working bodies of roller machines are two cylindrical cast iron rollers of the same diameter, located at angles and rotating towards each other at different speeds. The surface of the rollers is corrugated. The size of the gap between the rollers is set depending on the intended grinding coarseness. After each roller machine for sorting products by particle size, a sieving screen with a set of sieves of different numbers located one below the other is installed. When sifting, two fractions of grinding products are obtained: a pass, consisting of particles that did not pass through the sieve holes, and a pass, consisting of particles that passed through the sieve holes. Discharge from the upper sieve is the largest fraction with a particle size of 1.0-1.6 mm, the next largest fractions are called grits with a particle size of 0.31-1.0 mm and duns with a particle size of 0.16-0.31 mm . The finest fraction passing through forms flour with a particle size of less than 0.16 mm. The roller mill and sieving form a system. Systems can be tattered, which are used to crush grain into grains and duns, and grinding, which transform grains and duns into flour.

Repeated grinding can be simple if you get wallpaper or peeled flour, and complex if you get varietal flour.

Simple regrinding involves a single grinding process or a grinding process and a shortened grinding process. It is carried out as follows: the grain is sequentially crushed on several (3-4) roller machines. After each machine, the mixture is sifted and the flour is taken in the form of a pass from the lower sieve. Larger waste from the screens is sent to the next pair of rollers. This operation is carried out until all the particles turn into flour. Flour from all siftings is combined, control sifting is carried out and flour of one type is obtained. With wallpaper grinding, the yield of rye flour is 95%, the amount of selected bran is 2%, and the yield of wheat flour is 96%, with the yield of bran being 1%.

Complex repeated grinding can be without enrichment of grains and enrichment of grains. The first ones are intended for producing peeled and sifted rye flour, as well as for grinding triticale grain into peeled flour. In these cases, single-grade grinding is carried out with a yield of peeled flour of 87% and seeded flour with a yield of 63%, as well as two-grade grinding with a total yield of flour of 80%, in which 50-65% of peeled flour and 30-15% of seeded flour are obtained. With single-grade grinding, five torn and two grinding systems operate simultaneously. The latter can be with a reduced or developed enrichment process.

Enrichment of grains is carried out according to size and quality (ash content) on sieve machines, the main working part of which is a sorting sieve, divided into sections. Each section has a sieve with certain mesh sizes. Air is supplied from bottom to top through the sieve. The highest quality grains, rich in endosperm, pass through the first, smallest sieves, and are fed to the first grinding systems to obtain premium flour. The grains containing more shells, being lighter, are separated on subsequent sieves. They are then re-crushed, sifted and processed on sieve machines to separate the remaining shells and germ. After such processing, they are sent to grinding systems to form flour of lower grades.

Complex repeated grinding with a shortened grain enrichment process is used at small-capacity flour mills. They are designed to produce second-grade wheat flour with a yield of 85% with single-grade grinding. With two-grade grinding, 55-60% of first-grade flour and 23-18% of second-grade flour are obtained.

Complex repeated grinding with a developed process of grain enrichment is most widely used in the flour milling industry. They allow single-, two- and three-grade grinding. These types of grinding provide for the simultaneous operation of 4-5 torn and 10-11 grinding systems.