DEDICATED DRYING MACHINES MANUFACTURER
VACUUM FOOD DRYING TECHNIQUE
The use of vacuum combined with heat can be an effective method for drying. Lower moisture content
can be achieved when using a combination of vacuum and heat compared to heat alone (particularly
with products that are porous or have a very high surface area). The use of vacuum drying has shown
further improvement in quality of food products. It reduces thermal stress and sustains better colour and
texture of dried products compared to those that were air-dried. Rehydration kinetics is quite good.
A vacuum drying system consists of the vacuum chamber and source of the heat. Both oil-sealed and oil-
free (dry) mechanical vacuum pumps can be used. A condensate trap (typically cooled to very low
temperatures) is also used to pump and trap the liquid(s) to be removed. Base pressures of less than 0.1
Torr (1,333 × 10-4 bar) are often required, depending on the liquid to be removed and the temperatures
which we want to achieve. Care should be taken to protect oil-sealed pumps from the liquid and
operating the pumps properly to minimize the impact of the liquid vapours being ingested into the pump
(often with the use of a gas ballast and/or gas purge).
The vacuum drying process often involves multiple steps of applying heat and vacuum. Reducing the
pressure (applying vacuum) at the surface of a liquid (such as water) will allow the liquid to evaporate
without elevating the temperature. The evaporation of the liquid will continue until the product is dried
or until enough heat is removed (through evaporation) that the remaining liquid freezes. At this point the
drying process continues as sublimation which is much slower compared to evaporation. In general, this
is not desirable. The purpose of heat is to maximize drying while preventing freezing of the liquid. There
are several methods of applying heat to the product being dried. Some products have temperature
limitations which may impact the methods that may be employed. These methods include:
Dedicated Drying Solutions
Corporate Office
KDM Analytical
B-2/41 First Floor, Rohini
Sector-16, Delhi-110089
India
Tel
+91-9643480893
+91-9540666954
E -mail [email protected]
Application Lab
D-198, Mundka Industrial Area
Delhi-110081
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