Evaporation and concentration of food

1. EVAPORATION AND
CONCENTRATION OF FOOD
Submitted by ,
Unnimaya k
22412MFT007
M.Tech Food Technology

2. INTRODUCTION
• Evaporation is an unit operation commonly employed to remove water from dilute
liquid foods to obtain concentrated liquid products
• Removal of water from foods provides microbiological stability and assists in
reducing transportation and storage cost
• It’s used to pre-concentrate foods prior to drying, freezing or sterilization so this
saves energy in subsequence operation
• Common food products includes evaporated and sweetened condensed milk,
coffee extract , fruits and vegetable juices and nectars

3. HISTORY
 The first documented report on the scientific study of evaporation was the work of
Nils Wallerius (Swedish physicist , philosopher and theologian) in 1739 entitled
“Experiments , about vapour ascending to the air domain , made and sent to the
Academy” .
 The first record of the word evaporation come from the Latin word evaporare ,
meaning “ to disperse in vapour”
 The word vapour comes from the Latin word meaning “ steam”

4. THEORY OF EVAPORATION
• Sensible heat is transferred from heating medium(steam) to food to raise the
temperature to the boiling point of food
• The vapour pressure rises and bubbles of vapour in the liquid are formed due to
latent heat of vaporization supplied by the steam
• The vapour is then removed from the surface of the boiling liquid
• Rate of evaporation is determined by rate of heat transfer in to the food and rate
of mass transfer of vapour from the food

5. METHODS OF CONCENTRATION
• Solar concentration
• Open kettle
• Flash evaporator
• Thin film evaporator
• Vacuum evaporator
• Ultra filtration
• Reverse osmosis
Flash evaporation

6. Solar concentration
• Simplest method of evaporating water with solar energy
• This process was used in earlier times to obtain salt from sea water
• This process is very slow and suitable only for concentrating salt solutions
• Sub sized food material is brought in direct contact with heating medium to speed
up the concentration process
Flash evaporation

7. • Clean steam superheated at about 150 degree Celsius is injected in to food and
then pumped in to an evaporation tube where boiling occurs
• The boiling mixture then enters a separator vessel and the concentrated food is
drown off at the bottom and the steam plus water vapor from the food is
evacuated through a separate outlet
• Food lose volatile flavour constituent because of high temperature

8. Open kettle
• Use steam to concentrate foods in open kettle
• High temperature and long concentration time damage foods
• Thickening and burning of product to the kettle wall gradually lowers the
efficiency of heat transfer and slows the concentration process
• This method is apt for caramelized colour and typical flavour development in
foods high in sugar
• Examples – jams , jellies and certain type of soups

9. Thin film evaporation
• Food is pumped in to a vertical cylinder which has a rotating element that
spreads the food in to a thin layer on a cylindrical wall and the cylindrical wall is
heated by steam
• Water is quickly evaporated from the thin layer and the concentrated food is
wiped from the cylinder wall
• Concentrated food and water vapour are continuously discharged to an external
separator from which product is removed at the bottom and the water vapour
passes to a condenser

10. Vacuum evaporation
• Evaporation under vacuum can be done by operating thin film evaporator under
vacuum by connecting a vacuum pump or steam ejector to the condenser
• Several vacuum vessels can be attached in series so that the food moves from
one vacuum chamber to the next and there by becomes more and more
concentrated at each step
• The consecutive vessels are maintained at progressively higher degrees of
vacuum and hot water vapour arising from first step is used to heat the second
vessel ,so that heat energy is efficiently used

11. Freeze concentration
• Initially formed ice crystals during freezing process are removed with the help of
centrifugal process
• The resulting concentrated unfrozen food which passes through a fine mesh
screen
• This process is repeated many times to reach final concentration of food
• Applied in the commercial production of orange juice

12. Ultrafiltration and reverse osmosis
• Methods of concentrating foods employing pressure driven membrane separation
process
• UF membranes restrict macromolecules such as proteins but with moderate
pressure allows smaller molecules such as sugar and salt to pass through it
• Reverse osmosis operating under higher pressure
pressure and permit the passage of water but hold
back various sugars ,salt and larger molecules

13. EVAPORATOR
Made up of 3 functional sections
A heat exchanger ( Calandria ) – Which transfers heat from steam to the food
A means of separating the vapour produced –Entrainment separators
A mechanical or steam ejector vacuum pump – Mechanical pumps have lower
operating costs but higher capital costs than steam ejector pumps

14. WORKING
• The heat exchanger supplies the sensible heat to rise the product to it’s boiling
point and provide latent heat of vaporization.
• The boiled solution releases vapour and the separator separate this vapour and
concentrate , the resultant vapour is removed by condenser as condensate
• The process is carried out under reduced pressure & the heating medium is
steam
• For vacuum barometric leg condenser , vacuum pump and steam ejector are
used
• The evaporators may employ natural or forced circulation of the product

15. Factors influencing the rate of heat transfer
1. Temperature difference between the steam and boiling liquid
• There are two options to increase the temperature difference: to increase the
pressure and temperature of the steam or to reduce the temperature of the
boiling liquid
• In commercial vacuum evaporators the boiling point may be reduced to as low as
40 degree Celsius
• Both method increases the capital cost of equipment and also the energy needed
for processing

16. 2. Deposits on the heat transfer surfaces
• The fouling on the evaporator surfaces reduces the rate of heat transfer
• It depend on the temperature difference between the food and the heated
surface, and the viscosity and chemical composition of the food
3. Boundary films
• A film of stationary liquid at the evaporator wall is often the main resistance to
heat transfer
• The thickness of the boundary film is reduced by promoting convection currents
within the food or by mechanically induced turbulence

17. Factors influencing the economics of evaporation
1) Loss of concentrate or product quality – product losses are caused by foaming,
due to proteins and carbohydrates in food
2) High energy consumption – energy can be saved by re-using heat contained in
vapours produced from the boiling food by :
a) Vapour recompression
b) Preheating
c) Multiple effect evaporation

18. EVAPORATOR –TYPES
Evaporators are divided in to three groups
1. Natural circulation evaporator
Types :
• Evaporating pans
• Evaporating stills
• Short tube evaporator
2. Forced circulation evaporator
Climbing film evaporator

19. 3. Film evaporator
Types :
• Wiped film evaporator
• Long tube evaporator
a) Climbing film evaporator
b) Falling film evaporator
Falling film evaporator

20. Classification based on the nature of the heat
transfer surfaces
1. Tubular surface with natural or forced circulation
a. Horizontal tube evaporator
b. Vertical short tube evaporator
c. Rising film/ Ascending / climbing film evaporator
2. Flat heating surface: Plate evaporator
3. Stationary cylindrical surfaces with scraped surface evaporator

21. MULTIPLE EFFECT EVAPORATORS
• Several evaporators or effects are connected together
• Vapour from one effect is used directly as heating medium in the next
• This method is feasible only if the second evaporator is at a lower pressure than
the first
• The dilute feed enter the first effect where it is partially concentrated, then it flows
to the second effect for additional concentration and the final concentration is
done at the last effect

23. DIFFERENT FEED FLOW ARRANGEMENTS
Forward feed arrangement
Mixed feed
Parallel feed arrangement
Reverse feed/backward feed arrangement

24. a. Forward feed
b. Backward feed
c. Parallel feed
d. Mixed

25. FORWARD FEED
ADVANTAGES
 Least expensive and simple to operate ,no feed pumps required between effects
 Lower temperature with subsequent effects and therefore less risk of heat
damage to more viscous product
LIMITATIONS
 Reduced heat transfer rate as the feed becomes more viscous
 Rate of evaporation falls with each effect

26. BACKWARD FEED
ADVANTAGES
 No feed pump initially ,best quality steam used on the most difficult material to
concentrate , better economy and heat transfer rate
LIMITATIONS
 Interstage pumps necessary , risk of fouling
 Higher risk of heat damage to viscous product as liquor moves more slowly over
hotter surfaces

27. MIXED FEED
ADVANTAGES
 Simplicity of forward feed & economy of backward feed
 Useful for viscous foods
LIMITATIONS
 More complex
 Expensive

28. PARALLEL FEED
ADVANTAGES
 For crystal production
 Allows greater control over crystallization and prevents the need to pump
crystal slurries
LIMITATIONS
 Most complex and expensive of the arrangements
 Extraction pumps required for each effect

29. APPLICATIONS
• Product concentration
• Volume reduction
• Water / solvent recovery
• Desalination of sea water
• Dryer feed pre – concentration
• Crystallization

30. CONCENTRATED PRODUCTS
 Jam
 Jellies
 paste
 Sugar syrup
EVAPORATED FOOD PRODUCTS
 Concentrated vegetable juice
 Coffee extracts
 Refining sugar
 Salt
 Evaporated milk
 Sweetened condensed milk

31. ADVANTAGES
• Reduction in weight and volume
• Reduces transportation and storage cost
• Reduces deteriorative chemical reactions
• Save energy in subsequent operations
• Microbial stability and increased shelf life

32. DISADVANTAGES
• Physico-chemical changes that take place due to the exposure of product to high
temperature and pressure conditions
• As evaporation proceeds, the relatively dilute solution concentrates as a result
heat transfer coefficients reduce and load on the pumping system increases
• The solubility of solids in a solution decreases with increase in concentration
• Scale formation reduces the overall heat transfer coefficients

33. • Fouling may occur which causes microbiological damage to the products
• Crystallization may occur , that is undesirable for some products
• Increased viscosity of solution causing reduced heat transfer
• Reduction in nutritional quality in terms of vitamin and essential volatile
components

34. CONCLUSION
• Evaporation or concentration by boiling is the partial removal of water from liquid
foods by boiling off water.
• Evaporation increases the solid content and used to pre-concentrate foods prior
to drying, this saves energy in subsequent operations and reduces storage ,
transport and distribution costs
• Evaporation is more expensive in energy consumption than other methods of
concentration like membrane concentration and freeze concentration but a higher
degree of concentration can be achieved
• Changes to food quality that result from the relatively severe heat treatment are
minimized by the design and operation of the equipment

35. REFERENCES
• http://ecoursesonline.iasri.res.in/mod/page/view.php?id=19480
• Food processing technology principles and practices ( second edition) , P .
Fellows,2000
• Dairy process engineering , J.B.Upadhyay & Sunil M. Patel
• https://books.lib.uoguelph.ca/dairyscienceandtechnologyebook/chapter/eva
poration-and-dehydration/

36. Thank you…