freeze concentration of foods

2.  Concentration of liquid foods is a vital operation
in many food processes. Concentration is
different from dehydration.
 Generally, foods that are concentrated remain in
the liquid state, whereas drying produces solid or
semisolid foods with significantly lower water
content.

3. A liquid food is cooled with sufficient agitation. Ice
crystals nucleate and grow, and a slurry of
relatively pure ice crystals is removed.
Separation of these pure ice crystals leaves a
concentrated product.

4. Freeze concentration (FC) of fruit juices is a cold,
gentle and selective concentration procedure, in
which two distinctive steps, viz., ice
crystallization and ice separation from the
concentrate phase are involved.

5. a) First stage
Fruit juice is supercooled below its freezing point to
allow water to separate as ice crystals. This uses
either
i. Direct contact crystallizer, or
ii. Indirect contact crystallizer.

7. b) Second stage
The ice crystals are separated from the concentrated
fruit juices. This takes help of Presses, Filtering
centrifuges, Wash columns or a combination of
these.

9.  In freeze concentration it is desirable for ice
crystals to grow as large as is economically
possible, to reduce the amount of concentrated
liquor entrained with the crystals.
 This is achieved in a paddle crystallizer by
slowly stirring a thick slurry of ice crystals and
allowing the large crystals to grow at the expense
of smaller ones.

10. Heat sensitive substances
All products where maximum retention of
product quality is a key aspect
Where conventional concentration processes
cannot be used

11.  A direct freezing system or direct equipment to
freeze the liquid food
 A mixing vessel to allow the ice crystal to grow
 A separator to remove the crystals from the
concentrated solution

13.  The energy needed to freeze a unit of water is
much less.
 The low process temperature prevents
undesirable chemical and biochemical reactions
(minimum color change, non-enzymatic
browning and vitamin losses).
 As vacuum is not involved, the losses of low-
boiling flavor and aromatic esters are completely
avoided

14.  Major problem is the loss of soluble solids of the
juice in the separated ice.
 The final concentration of the concentrated juice
is as low as 40-55% dry matter, due to steep
increase in the viscosity of ice-concentrated
mixture.

15. As the juice concentrates, there is increase in
viscosity which retards water crystallization.
Multi-stage FC overcomes this to a great extent.
In such process, the ice crystals are separated out
at the end of each cycle and the remaining
concentrate is fed to the succeeding crystallizing
compartments.
Here, the ice crystals are separated at different
levels of concentration and viscosity.

16.  Fruit juices,
 milk products,
 vinegar,
 coffee and tea extracts,
 beer and wine, and
 other flavor products.
 Concentration of alcoholic beverages is one
application where freeze concentration is
superior to other techniques.