processing and preservation of food by evaporation and concentration

1. Presented by,
Rasmi. P. K
22412MFT004
M. Tech Food Technology
DSFT, IAS , BHU

2.  Evaporation, or concentration by boiling, is the partial removal of
water from liquid foods by boiling off water vapor.
 Increases the solids content of a food and hence preserves it by
the reduction in water activity

3.  Evaporation differs from dehydration, since
the final product from evaporation remains
in liquid state
 It also differs from distillation ,since the
vapors produced in the evaporator are not
further divided into fractions
 A typical example of evaporation is , in the
manufacture of concentrated tomato
paste , usually around 35% to 37% total
solids obtained by evaporating water vapor
from tomato juice , which has an initial
concentration of 5%-6% total solids

4.  Evaporation provides :
Microbial stability
Reduce transportation cost
Reduce storage cost
Food becomes more attractive
 Pre-treatment to concentrate foods
prior to drying, freezing or sterilization

6. Sensible heat is transferred from steam to food
– to raise the temperature to the boiling point of food
Latent heat of evaporation is then supplied by the steam
– to form bubbles of vapor which leave the surface of boiling
liquid
Rate of evaporation is determined by
– rate of heat transfer into the food
– rate of mass transfer of vapor from the food

7. 

8. &

9. Heat supplied by steam = Sensible heat +Latent heat of vapor
• Rate of heat transfer across evaporator walls & boundary films is
found using equation
Q = U A (𝜃𝑠 - 𝜃𝑏
For the majority of an evaporation process,
• the rate of heat transfer is the controlling factor
• the rate of mass transfer only becomes important when the liquor
becomes highly concentrated.

10.  Solar concentration
 Open kettle
 Flash evaporator
 Thin film evaporator
 Vacuum evaporator
 Freeze concentrator
 Ultra filtration and reverse osmosis

11. Factors influencingrate of heat transfer
 Temperature difference
between steam and boiling
liquid
 Deposits of heat transfer
surface
 Boundary films
Factors influencingeconomicsof
evaporation
 Loss of concentrate or
product quality ( by foaming)
 High energy consumption

12. • Made up from 3 functional sections
 A heat exchanger
 A means of separating the vapor produced
 A mechanical or steam ejector vacuum pump

13.  Simplicity
 Steam is used only in the first effect
 The use of vapour as the heating
medium in additional effects results in
obtaining higher energy use efficiency
from the system

14. Methods of feeding

16. • Rate at which heat can be transferred to liquid
• Quantity of heat required to evaporate each kg of water
• Pressure at which evaporation takes place
• Any changes which may occur in food stuff during
evaporation process

17. • Product concentration
• Dryer feed pre-concentration
• Volume reduction
• Water / solvent recovery
• Crystallization

18. DDHDFJHWEFJSDBVJERHGD
 Concentrated vegetable juice
 Coffee extracts
 Refining sugar
 Salt
 Concentrated milk products
CONCENTRATED FOOD PRODUCTS
 Jam
 Jelly
 Tomato paste
 Sugar syrup

19. • To reduce the weight and volume
• Saves energy in subsequent operations and reduces storage, transport and
distribution costs
• Higher degree of concentration
• Greater convenience of the consumer and the manufacturer – Fruit drinks,
concentrated soups, tomato paste
• Changes in food quality due to severe heat treatment are minimized by
the design and operation of the equipment
• More expensive in energy consumption than other methods of
concentration viz. membrane concentration and freeze concentration