Batch dough kneading machine
- Added: 03.07.2014
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Preparation of dough, its handling, proofing and baking are the main production processes of baking, predetermining the quality of the finished product. The equipment for these processes constitutes the production line.
The composition and layout of dough preparation units and dough cutting lines, the principle of operation and design of dough mixing, dividing and molding machines depend on the selected technological schemes of production and properties of the processed raw materials. As a rule, bakery equipment having the same functional purpose, but processing rye or wheat semi-products, differs significantly in the design and nature of the movement of the working elements.
In the production lines of bakeries, periodical machines and devices are becoming increasingly widespread, allowing for a clear response to fluctuations in demand and quickly changing the range of products produced. The equipment of production lines should provide the possibility of regulating the technological parameters of semi-finished products in a wide range of cases, since a significant amount of the main raw materials supplied to enterprises is characterized by reduced bakery qualities.
A special place in bakery production is occupied by ovens, which are the leading equipment, on which the production capacity and economic indicators of the enterprise depend.
The creation of new technologies for the production of bread products is the basis for improving the technical base of the bakery industry, which leads to an increase in the quality indicators of the machines and apparatus produced, an expansion in the range of equipment and at bors.
The purpose of my work is to familiarize myself with the equipment for kneading test semi-finished products. It is detailed to sort the principle of work of the dough mixing A2XTM330 car of periodic action with a podkatny dezhy volume of 330 l. and calculate its main characteristics.
1 Equipment for kneading test semi-finished products
1.1 Purpose and classification of test kneading machines
Baking dough kneading consists in mixing raw materials (flour, water, yeast, salt, sugar and other components) into a homogeneous mass, giving this mass the necessary structural and mechanical properties, saturation of its air and thus creating favorable conditions for subsequent technological operations.
Kneading is not a simple mechanical process, it is accompanied by biochemical and colloidal phenomena, an increase in the temperature of the kneaded mass.
Dough kneading machines, depending on the recipe composition and the characteristics of the assortment, should have different effects on the dough and its subsequent ripening. As a result, the quality of the finished product depends on the work of dough kneading machines.
Depending on the structure of the working cycle, dough kneading machines are divided into batch machines and continuous machines. Intermittent machines are equipped with stationary kneading vessels (desks) or interchangeable (rolling desks). deji are immobile, with free or forced rotation.
According to intensity of action of working member on treated mass, dough kneading machines are divided into three groups:
- normal slow-moving - the working process is not accompanied by noticeable heating of the dough, specific energy consumption 5-12J/g;
- fast (machines for intensive kneading of dough) - the working process is not accompanied by noticeable heating of the dough at 5-7 ° C, 20-40 J/g is used for kneading;
- super-exhaust (super-intensive) machines, kneading is accompanied by heating of the dough by 10-20 ° C and requires a device for water cooling of the mixing chamber body or preliminary cooling of the water used for dough, 30-45 J/g is consumed for kneading.
The design of the kneading machine is largely determined by the properties of the kneaded raw materials. The elastic-elastic dough requires more intense scrubbing than the plastic dough. For kneading of dough from wheat flour of higher and 1 grades, showing pronounced elasticity and elasticity, it is necessary to use machines with a complex trajectory of movement of the kneading organ in one plane or with a spatial trajectory of the blade, as well as machines with two rotating kneading organs.
For kneading plastic dough (from wheat wallpaper or rye flour), machines of a simpler design can be used, for example, with a rotating kneading member.
Depending on the trajectory of kneading organs, kneading machines with simple, rotational, planetary and spatial motion are distinguished. By the location of the axis of the kneader, machines with horizontal, inclined and vertical axes are distinguished.
According to the type of semi-finished products obtained, machines for kneading thick opars and dough with humidity 30... 50%, for the preparation of liquid opars, starters and nutrient mixtures with humidity 60... 70% are distinguished.
Depending on the control system used, dough kneading machines are available with manual, semi-automatic and automatic control.
The baking dough kneading process consists of three consecutive stages: mechanical mixing, structure formation and plasticization.
Mechanical mixing is completed by forming a three-phase mixture with high uniformity of distribution of components. During mixing, dry components are moistened, dispersed, aggregated. This step should be carried out as quickly as possible. In this case, uniform mixing of the components with minimal energy consumption can be achieved.
The second stage - structure formation - is characterized by leveling the moisture content, diffusion of moisture into the flour particles, swelling of proteins and transition to a solution of water-soluble flour components. Here, the mass shear force and hence the energy consumption of the mixer drive increases markedly. When swelling, most of the moisture is absorbed by protein substances. The water absorption of flour starch reaches 30%, but the rate of moisture absorption is small higher than proteins. The viscosity of the dough increases.
The flow rate of the second stage is influenced by the properties of the flour, the degree of grinding of the starch grains, the temperature and the recipe additives introduced into the dough. When moisture is absorbed, proteins greatly increase in volume, forming an gluten skeleton that binds swollen starch grains and insoluble flour particles. The second stage of kneading does not require vigorous study.
The third stage - plasticization - is accompanied by structural changes in starch grains and the formation of an gluten lattice that binds starch grains. At the same time, they are partially ground and enveloped with protein films, which also undergo structural changes. Helical molecules of polypeptides split and loosen the structure of proteins, forming gluten films. Such film structuring creates a good gas-retaining dough skeleton.
The third stage requires enhanced mechanical action, since gluten molecules are simultaneously destroyed with the formation of gluten films. At the third stage, the dough structure is equalized and ground, which in the future during fermentation contributes to the formation of a uniform fine porous
When comparing the efficiency of the kneading organs, it is necessary to take into account that the structure formation mechanism during the implementation of different types of deformation during kneading varies significantly. During strain deformation protein chains are drawn and oriented in direction of deforming forces. Stretching provides a significant number of long chains that are less torn into individual fragments, reduce the number of polymer mesh nodes, and extend longer. This gluten frame provides greater extensibility and low elasticity of the dough.
During shear deformation, the mechanical destruction of the polymer proceeds more intensively, the chains are torn into relatively short fragments, which, when interacting, form a fairly frequent mesh, which acquires greater elasticity (strength) and less extensibility.
Given the small size and relatively rare arrangement of protein macromolecules in flour particles, without the application of deformations, the compression-shift when kneading macromolecules unfold slowly and less fully, which should reduce the proportion of protein chains involved in structure formation, which is especially evident when the amount of protein in the flour decreases.
Thus, shear deformation increases the viscous-elastic properties of test semi-products to a greater extent, and stretches - de formational. The rational combination of such effects provides an improvement in the quality of bread, in particular, its form stability, especially when processing weak flour.
Plasticization should occur at such shear rates of the material when its continuous medium is not disturbed, and sliding and friction on the working surfaces are minimized, significant movement (transfer) by the working elements of the plasticizer of individual volumes of dough inside the mixing chamber is excluded. A promising method of plasticisation is when the working elements do not slide in the mass of the material being treated, but are rolled and deformed during pinching.
Increasing the degree of mechanical processing accelerates the process of dough maturation, improves its rheological properties and gas-retaining ability. This is due to the faster formation of sticky wines, the accumulation of the colloidal-soluble phase of proteins and their water-soluble fraction. Machining also affects the properties of starch, which binds about half the moisture of the dough. It has been experimentally proven that the mechanical effect on starch, which leads to damage and grinding of starch grains, significantly enhances the processes of starch hydrolysis under the influence of acids and amylolytic enzymes.
Intensive kneading has a positive effect on the water-absorbing ability of flour, provides the possibility of maintaining the normalized moisture of dough from flour of different bakery dignity and, accordingly, compliance with the established standards of product yield. As an indicator characterizing the degree of mechanical treatment of dough during kneading, it is customary to use the value of specific work of kneading
a = A/m
A- work of kneading, kJ;
m- dough weight in dough, kg;
A = Nj/n
N - power of the motor of the dough kneader, kW;
j - duration of kneading, s;
n - drive efficiency;
a = N/( nP),
P - machine capacity, kg/s.
In terms of specific work, all dough kneading machines can be divided into the following groups: for ordinary kneading, a = 2... 4 J/g; for enhanced machining a = 9... 11 J/g; for intensive kneading a = 25... 40J/g.
Replacement intensity index is used as additional characteristics
n - speed of blade rotation (swinging).
It was found that enhanced mechanical treatment is advisable to use in combination with large thick supports, and intensive kneading - with liquid test semi-products.
Intensive mechanical processing of the dough during kneading allows you to reduce the duration of fermentation of the dough before cutting to 20... 30 min instead of 1.5... 2.0 h with normal kneading. This gives an average of 1% save on flour solids for fermentation. In addition, the specific volume of bread increases by 15... 20%, the porosity structure, color and elasticity of the flesh are improved.
Studies of the technological efficiency of intensive machining of dough depending on the quality of flour, the presence of recipe additives, various kinds of enhancers and the dough preparation scheme have shown that the degree of intensity of machining should vary widely depending on the quantitative and qualitative characteristics of the gluten of the flour.
So, for dough of flour with weak gluten, the optimal level of energy consumption for kneading at a measure of 3 times less than for dough of flour with strong gluten.
Intensive kneading machines have a high energy intensity, so in the face of a significant increase in the cost of electricity, it is advisable to use them only after taking into account all existing factors.
An effective method of reducing energy consumption is a two-stage method of preparing dough with an exposure between stages. First, it is necessary to homogenize the components in a speed mixer by rapidly contacting the dispersed flour particles with the dispersion medium of the liquid semi-product. A relatively small proportion of energy is consumed in the homogenization step.
After homogenisation mechanical treatment of dough is carried out - plasticisation, which provides maximum energy consumption for formation of semi-finished product. Fermentation between stages not only significantly improves the technological properties of dough and bread quality, but also, due to the intensive course of biochemical and colloidal processes, significantly reduces the energy consumption for kneading.
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