Упрощенная HTML-версия
Lecture 11: Food products drying process - convection, vacuum
sublimation, etc..
Plan:
1. Purpose of drying foods
2. drying methods, characterization
3. Combined drying product characteristics
In many processes for drying the product under intense attack a number of
factors to increase shelf life, expanding the range, as well as preserving the
nutritional value of foods.
Drying -
the removal of moisture from the wet solid, pasty or liquid food
environments by evaporation and removal of the resulting vapor. In this process,
a transition occurs from a solid material moisture in vapor or gas phase. Its speed
in many cases determined by the rate of diffusion in the transfer of moisture in
solids. In the production of many food products drying, usually operation is
mandatory and is a relatively energy intensive process step process. In the
manufacture of some foodstuffs may be preceded by drying, partial removal of
free moisture from the materials by other methods, such as squeezing presses,
centrifugation, evaporation to increase the concentration of solids. When
choosing a method of drying is necessary to bear in mind that food materials
have a number of distinctive features: low temperature resistance, prone to
oxidation and degradation prone to warping and loss of the presentation, the
presence of active biochemical and chemically active substances. Therefore,
methods must use the combined heat supply, which allows the most efficient
heat the material to a drying temperature. The rationale is the use of combined
drying units.
By way of heat supply to the material to be dried drying methods are
divided into:
- Convection or air, drying - heat supply is carried out by direct contact
with the drying agent a dried material;
- Contact drying - by transferring heat from the coolant to the material
through the wall separating them;
- Radiation drying - by transferring the heat of infrared emitters;
- Dielectric drying - by heating the material in a field of high frequency
currents;
- Freeze-drying - drying under high vacuum in a frozen state.
Crystallization
is one of the most common and most effective methods of
obtaining pure substances. By crystallization from the liquid phase substance is
released in the form of crystals of various geometric shapes bounded by flat
160