Physical and chemical changes in the dough during baking.
During baking occur physicochemical changes dough. Especially significant changes occur in proteins and starch flour, play a fundamental role in the formation of biscuits structure. When warming up the dough to a temperature 50-70 ° C test proteins are denatured and coagulated, freeing the water absorbed during swelling and starch swelling and partially gelatinized liberated water.
Dehydrated and coagulated gluten proteins and partially gelatinized starch form a porous skeleton, which is adsorbed on the surface of the fat in the form of thin films.
At a temperature of about 60 ° C ammonium carbonate decomposes with evolution of gaseous substances - carbon dioxide and ammonia. Bicarbonate of soda decomposes at 80- 90 ° C with evolution of carbon dioxide. At higher test pressure temperature and volume of gaseous products formed increases, thereby changing the volume of the dough pieces and the pores in the test significantly increased. The loosening test the important role played by water vapor generated in the dough during baking.
During baking, there is a gradual dewatering of the surface layers and the formation of a crust on the dough surface. It is important that the formation of crusts place not at once but gradually, because it prevents the occurrence of an increase in volume of the dough pieces. Therefore, the first baking process is conducted at a low temperature baking chamber humidified environment that promotes the formation of a thin crust at a later period.
During baking, the test chemical changes occur. Marked reduction in the amount of sugars in the cookie, which is explained by their partial decomposition under the influence of the high temperature environment of the baking chamber. The crucial role in coloring crust pastry products belongs to the interaction of reducing sugars with protein breakdown products, ie. E. Melanoidins. Along with this products on crust color and generally affects baking soda, the presence of which gives the product a yellowish color during baking.
Total protein content of the biscuits in a baking process is almost unchanged, but for certain types of proteins significant quantitative changes observed. Such changes undergo individual protein species, are the result of exposure to temperature in the baking process.
The amount of insoluble starch decreases, due to its partial hydrolysis during baking and form a soluble starch and dextrin.
Also reduced the amount of fat that should be explained by the release of fat from the test result in unstable adsorption of it to the surface of the micelles.
Alkalinity cookie baking is significantly reduced, apparently due to the interaction with the alkali chemical disintegrants substances having an acid reaction, and also partly as a result of volatilization of ammonia formed by decomposition of ammonium carbonate.
Mineral content is not changed in a baking process. The amount of organic phosphorus is reduced.
Optimum baking mode. When selecting the optimal mode baking parameters necessary to consider influence of steam-air medium in the baking chamber and colloidal physicochemical processes occurring in the test, which predetermine eventually, obtaining products with strictly defined quality indicators. Along with this, it is necessary to ensure optimal conditions for heat exchange in the baking chamber, allowing the most efficient and cost-effective to conduct the process.
Results of experimental studies allow us to recommend the next best cookie baking mode.
1. Initially, the baking process should take place at a high relative humidity (60-70%) and relatively low temperature (not above 160 ° C) medium baking chamber favoring the flow of the colloid and physico-chemical processes in optimum conditions.
High relative humidity environment baking chamber achieved artificial humidification test intensifies heating, promotes protein denaturation process top and partial starch gelatinization and degradation of chemical disintegrants to release gaseous products, disintegrating dough.
The low temperature in combination with high relative humidity environment baking chamber eliminates the possibility of the formation of a crust on the surface of the articles in the first baking period. The elastic film formed on the surface of the product, no significant resistance Ras Shiryaev gases within the dough pieces that contributes to the gradual rise of products and consequently the formation of the porous structure.
2. The second baking period is characterized by a variable temperature environment mode baking chamber, with a gradual increase in temperature to 350-400 ° C.
The relative humidity of the environment of the baking chamber can be reduced, thus moistening the baking chamber in this baking period does not produce.
In the second period, and baking continues generally completed colloidal and physico-chemical processes in the test associated with the denaturation and coagulation of protein, partial gelatinization of starch and expansion of chemical disintegrants.
3. The third period is characterized by baking a constant temperature, reduced to 250 ° C. In this period there is a final product fixing structure to form a crust on their surface and completes the process of removing excess moisture.
Duration baking cookies usually ranges 4-5 minutes. When optimally baking duration is reduced to 3,5 minutes.
Baking biscuits and crackers typically applies a variable temperature control with optional baking chamber humidified environment. First 4 min ambient temperature baking chamber gradually increases from 230 to 260 ° C, then gradually decreases to 205 ° C. The total duration of the baking process for ordinary biscuits 12-15 minutes, dietary biscuits and crackers 5-10 minutes. Longer baking biscuits compared with biscuits because the moisture content and thickness of the dough pieces of these products above the maximum ambient temperature in the baking chamber below.
For baking pastry products used furnaces of various designs, which can be classified by the method of heating the baking chamber:
a) Zharov, accumulating the heat baking chamber walls during the direct combustion of fuel therein;
b) channels, wherein the coolant is a gas produced by the combustion of fuel and transfers the heat to the baking chamber through the walls of the channels;
c) a steam-heated, wherein the heat-transfer surface are Perkins tube;
g) tunnel direct gas burning in the baking chamber by means of burners, or heated by electricity using the heat-transfer surface in the form of resistance elements.
According to the construction of the hearth baking furnaces distinguished from stationary and retractable conveyor hearth.
Most are mechanized conveyor furnace podami, which are also divided into the following main types: a) chain, b) of cradle, c) boring, d) band.
Typical equipment for baking cookies are gas tunnel kiln with a continuous conveyor belt or chain hearths.
In the case of tunnel ovens with conveyor chain hearths sheets with test workpieces are mounted on chain conveyors which move along the furnace and heated by two rows of burners located above and below the conveyor.
However, these furnaces in recent years replaced by more sophisticated gas tunnel furnaces of continuous or perforated mesh steel strips, in which the dough pieces are stacked directly on the belt of the baking chamber. Preference is given to the single-furnaces.
Adjusting the conveyor advance speed is a CVT or speed regulator. Gas burners are arranged in the baking chamber in accordance with the process of baking mode. A higher temperature environment in a certain area of the baking chamber is achieved more frequent location burners. Moreover, the baking chamber temperature of the medium can be adjusted by changing the gas feed to the burners until disable certain quantity.
Gas tunnel ovens also have the advantage that heating of the baking chamber to working temperature is carried out 2-3 hours, while in channel furnaces it takes 2-3 days. Cooling of the furnace in case of emergency repairs made in the shortest time.
Electric furnaces have the advantage over other constructions of furnaces and will be introduced at the enterprises, producing pastries in the near future, especially in areas with cheap elektrrenergiey. the thermal regime, exclude the possibility of explosion in the baking chamber (which may occur in gas furnaces), no combustion products, increased efficiency of the furnace efficiency more easily and automatically adjusted in these furnaces.
With a stationary hearth furnace used only in small enterprises in the formulation of a wide range of small quantities requiring a different temperature regime. These furnaces are characterized by low productivity, low-efficiency, large size, manual loading and unloading products, so they have recently ousted furnaces heating channel.
Rotary kilns designed construction provide the optimum mode of the baking flour confectionery and different performance.
Physical and chemical changes in the dough during baking.