Food engineering operations are employed in food industries for production of good quality palatable and stable foods.Food engineering operations convert raw agricultural commodities into canned, frozen, dehydrated, formulated and otherwise modified forms of food.

1. Elementary Food
Engineering
Submitted by:
Sukhveer Singh FST-13211
Centre of Food Science & Technology
Institute of Agricultural Sciences
Banaras Hindu University

2. Contains:
Thermal Treatments
Sterilization
Blanching
Food Dehydration
Dehydration equipment
Freezing
Freezing technology and equipment
Evaporation
Evaporators
Mathematical expression of heat load
Abhilasha Singh
Sukhveer Singh
Ankita Joshi
Mithilesh Singh

3. • Food engineering operations are employed in food
industries for production of good quality palatable
and stable foods.
• These scientific approaches can control the spoilage
of package foods.
• The knowledge of the engineering (heat treatment
and heat transfer) have provided necessary impetus
to the development of large food and canning
industries.
Elementary Food Engineering:

4. Some of the basic food engineering operations
Thermal treatments
It serves to reduce the concentrate of
microorganisms in the foods when they are preserved
by heat.
It may also inactivate the existing enzymes in foods.
Categories of heat treatment process:-
Heating the foods below 100°c temperature.
Heating the foods to a temperature of 100°c.
Heating the foods above 100°c.

5. • Pasteurisation is usually done below 100°c
temperature to kill all pathogenic organisms and also
kill some of the spoilage organisms present in the
food.
• A Pasteurization process can destroy pathogens in the
milk but does not effect the organoleptic properties of
milk.
• Pasteurization process was first developed in 1864 by
Pasteur to prevent abnormal fermentation in wine.
• In present days, pasteurization is applied to a wide
range of foods, like; milk, canned and bottled fruits,
cream, ice-cream, fruit juices, pickles, beers etc.

6. • Pasteurisation of milk is performed by heating
every particle of milk to at least 61°c and
holding it at that temperature for 30 minutes or
heating the milk to 71°c and holding it at 71°c
for at least 15 seconds.
• Pasteurisation destroys most of bacteria present
in milk thus improves the keeping quality of
milk.
• The taste of milk is not affected by
Pasteurisation.

7. • Type of Pasteurisation
– The batch type
– The continuous type or high temperature short time
• Continuous Pasteurisation :-
– The foods are pasteurised through plate heat
exchangers.
– It comprises four stages-
1. Pre heating or regeneration
2. Heating
3. Holding
4. Cooling

8. • Sterilisation of foods is carried at temperatures
above 100°c.
• Method of Sterilisation:-
1. Sterilisation of food in containers
2. Sterilisation of food before placing in the container
• Sterilisation of food in containers can be done by
following methods
1. Indirect heating by saturated steam
2. Forced convection of hot air
3. By direct flame contact

9. Type of Sterilisation
• Batch Steriliser
– Labour requirement is high
– Flexible
– Horizontal and side loading type occupy more space than top
loading and vertical types
– Steam pressures are in the range of 350-415KN/m2
• Continuous steriliser
– Steam and water consumption are higher
– Three types
• The continuous pressure cooker-cooler
• The continuous rotary steriliser
• The hydrostatic steriliser

10. Blanching is done to inactivate enzymes and to destroy the
peroxides.
Blanching is the process of the process of heating the food
rapidly to a predetermined temperature, holding it at that
temperature for a definite period and then either cooling the
material or passing it to subsequent processing without delay.
Beside destroying enzymes, following changes in food may also
be brought about by blanching-
• Cleaning of raw material and reduction in bacterial load.
• Softening and shrinking of foods which help to fill the
containers.
• The texture of dehydrated foods is improved by blanching.
• Heat sensible vitamins are lost.
• Leaching of water soluble nutrients.
Blanching:

11. Blanching can be done by two methods-
1. Immersion blanching, with the help of hot
water
• It carried out by two ways-
i. Passing the food at controlled rate
through a perforated drum rotating in
a tank of water. The hot water is
thermostatically controlled at
temperatures of 75-100°c.
ii. Food is suspended in water and
heated to blanching temperature.
Remarkable loss of water soluble
materials.

12. 1. Steam Blanching
i. Saturated steam is
used.
ii. Food is passed through
a steam chamber on a
mesh belt conveyor or
by a screw conveyor.
The residence time of
blanching is controlled
by controlling the speed
of conveyance.
iii. The loss of water
soluble material is less
in steam blanching.

13. Drying and Dehydration
• Removes water
• Occurs under natural conditions in the field
and during cooking
• Makes foods
– Lighter
– Take up less space
– Cost less to ship

14. Factors that Affect Heat and Liquid
Transfer in Food Products
• Surface area
– The greater the faster the product dries
• Temperature
– The greater the difference between the product and
drying medium, the greater the rate of drying
• Humidity
– The higher, the slower the drying
• Atmospheric pressure
– The lower, the lower the temperature required to
remove water

15. Purpose
• Remove enough moisture to prevent microbial
growth
• Sun drying may be too slow and organisms
may cause spoilage before the product can be
thoroughly dried
– In these cases salt or smoke may be added to the
product prior to drying

16. Dehydration
• Almost the complete removal of water
• Results in
– Decreased weight
– Increased amount of product per container
– Decreased shipping costs

17. TRAY DRYER
It consists of an insulated cabinet in which
trays are placed one over other with gap in
between.
advantage: - 1. Relatively cheap to build and
maintain.
2. Flexbility to accomodate various food
products.
The vacuum makes the possibility of main
taining lowest possible pressure in the space
around the food product.

18. DRUM DRYER
 The drum dryers are consist of one or more
hollow metal cyslinders.
 These drums are heated by circulating steam,
hot water or other high temperature heat
transfer liquid through the drums.
A single drum dryer consists of only one drum,
while the double drum dryer has two drums
or rolls.
 twin drum.

19. FREEZE DRYING
 In a freeze drying system, dehydration takes
places in three stages first, the water of product is
removed by formation of ice crystals.
 In freeze drying system, the size and shape of
original food products can be retained and the
shrinkage is negligible.
 In conventional freeze dryers, condenser is
provided to remove the water vapour formed
during the process and heating system to provide
the necessary latent heat of sublimation to the
frozen product.

20. Drying Methods
• Air Convection
• Drum
• Vacuum
• Freeze

21. Solar Evaporation
• Oldest
• Slow
• Only used to concentrate salt solutions in
human made lagoons

22. Home Drying
• Food dehydrators
• Microwaves
– Recommended for drying herbs only
• Ovens
• Outdoors
• Drying time depends on the food type,
thickness and type of dryer

23. Food Dehydrators
• Efficiently designed to dry foods at 140°F
• Major disadvantage is limited capacity

24. Sun Drying
• Fruits are safe to dry outdoors due to their high
sugar and acid content when conditions are
favorable for drying
• Not recommended for vegetables or meats
• Conditions needed for outdoor drying
– Hot, dry, breezy days
– Minimum temperature of 85°F, with higher
temperatures being better
– Humidity below 60%
– Several days

25. Freezing:
• The frozen food industry was born in the 1920’s
• Clarence Birdseye produced the first frozen fish
Freezing is the unit operation in which the temperature
of a food is reduced below its freezing point and a
proportion of the water undergoes a change in state to
form ice crystals. The immobilization of water to ice and
the resulting concentration of dissolved solutes in
unfrozen
water lower the water activity
(aw) of the food

26. BASIC PRINCIPLE
1) Very low temperatures inhibit growth of micro-
organisms and limit enzyme and chemical activity.
2) The formation of ice crystals draws available water
from the food, also preventing growth of micro-
organisms.

27. • Fruits (strawberries, oranges, raspberries) either whole or
pureed, or as juice concentrates
• Vegetables (peas, green beans, sweet corn, spinach, and
potatoes)
• Fish fillets and sea foods (cod, plaice, shrimps and crab meat)
including fish fingers, fish cakes or prepared dishes with an
accompanying sauce
• Meats (beef, lamb, poultry) as carcasses, boxed joints or cubes
and meat products (sausages, beefburgers, reformed steaks)
• Baked goods (bread, cakes, fruit and meat pies)
• Prepared foods (pizzas, desserts, ice cream, complete meals
and cook–freeze dishes).
COMMERCIALLY AVAILABLE
FREEZED FOOD PRODUCTS

28. FREEZING CURVE

29. Chemical changes
– Enzymes in vegetables
– Enzymes in fruit
– Rancidity
Texture Changes
– Expansion of food
– Ice crystals
How Freezing Affects Food

30. Undesirable physical changes
- Freezer burn
• Package properly
• Control temperature fluctuations in storage.
- Oxidation
• Off-flavors
• Vitamin loss
• Browning
- Recrystallization

31. ISSUES with FROZEN FOODS
1. Chemical reactions can occur in unfrozen
water.
A. Some foods blanched or sulfited before
freezing.
B. Vacuum packaging to keep out oxygen.

32. ISSUES with FROZEN FOODS (cont.)
2. Undesirable physical changes
A. Fruits and vegetables lose crispness
B. Drip loss in meats and colloidal type foods
(starch, emulsions)
• Freeze product faster
• Control temperature fluctuations in storage.
• Modify starch, egg systems, etc.

33. Consider:
– Size
– Shape
– Efficiency
– Defrosting features
– Available floor area
– Amount of freezer space needed
Freezer Selection
A freezer should be kept at -18oC to -25oC.

34. TYPES OF FREEZING
• Immersion freezing (Ex- Shrimps)
• Plate Freezing
• Blast Freezing
(Fruits & eggs)

35. • Belt freezing (Vegitables)

36. • Fluidised Bed Freezing
• Cryogenic freezing

37. MECHANICAL FREEZER
SPIRAL-TUNNEL-OTHER
LN2 IMMERSION
OR
CRYOGENIC TUNNEL
FREEZER
50-75% OF FREEZING
25-50% FREEZING
(CRUST FREEZING)
DELICATE OR YIELD
SENSITIVE PRODUCT
BEST CRYOGENIC APPLICATION…
CRYO-MECHANICAL FREEZING

38. ADVANTAGES OF FREEZING
• Preservation of color, flavor and
nutritive value.
• Microorganisms do not grow and
multiply during frozen storage.
• Freezing kills some vegetative cells.
Spores survive, and may grow when
the food is thawed.

39. DISADVANTAGES OF FREEZING
• Deterioration of texture depending on the nature
of food and the freezing process
• Minor losses in nutritive value and quality
• Expensive preservation operation, and
requires energy even after the operation is
complete
• Depending on the storage conditions, frozen foods
may also lose water

40. • Evaporation is an unit operation to concentrate a
solution with a volatile solvent.
• It also can defined as an unit operation in which water or
volatile solvent are removed to obtain concentrated
liquid products from dilute liquid food.
• Evaporation also provide microbiological stability and
reduce transportation and storage costs.
• Evaporation is basically a separation step which uses heat
transfer to separate products presenting differences at
boiling point. This technology results in several different
downstream processes such as concentration,
crystallization and drying.
Evaporation:

41. Evaporation is carried out in evaporators which consist of
a heat exchanger which supplies sensible heat and latent
heat of evaporation to the feed.
Normally saturated steam is used as the heating medium
in food industries.
The product inside the evaporator chamber is kept under
vacuum, this increase the temperature difference
between steam and product.
Thus the product boil at lower temperatures.
The other important part of evaporator is a separator to
separate vapor from the concentrated liquid and a
condenser to cause condensation of the vapor and its
removal from the system.

42. Diagram of single effect evaporator

44. Multi effect evaporator

45. The heat load of a single effect evaporator:
The oveall rate of heat transfer ‘q’ through the heating surface of
an evaporator is the product of three factors as given below:
q = UA∆T
Where, U = overall heat transfer coefficient
A = area of the heat transfer surface
∆T = overall temperature drop
The overall rate of heat transfer is equal to the product of mass
flow rate of the heating medium usually steam and the latent
heat of condensation of inlet steam.
q = UA∆T = msλs
Where, ms= mass flow rate of steam, kg/s or kg/hr
λs = latent heat of condensation of inlet steam k Cal/kg

46. Let, the heat losses from the system by convection and radiation
from hot surface are neglected, i.e. all the heat given up by the
condensing steam is transferred for evaporation of water from
the liquid food.
msλs = sensible heat gained by liquor + latent heat
of vaporisation of water
= (mf−mp) λ + mfCp (Tp−Tf)
mf = mass flow rate of feed, kg/s
mp= mass flow rate of thick liquour or product, kg/s
λ = latent heat of condensation of inlet steam k Cal/kg
Cp = Specific heat of feed, k cal/kg ℃
Tp= temperature of thick liquor, ℃
Tf= temperature of feed, ℃

47. Material balance:
The overall material balance of evaporator can be prented by the
following equation:
mf = m + V
Where, V= mass of solvent vaporised in the evaporator, kg/s
The material balance on the liquid
mf (1 −xf) = m (1-xp) + V
Where xf= mass flow rate of solid fraction in feed, kg/s
xp= mass flow rate of solid fraction in product or
thick liquor, kg/s
The economy of evaporation=
𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑒𝑑/ℎ𝑟
𝑆𝑡𝑒𝑎𝑚 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑/ℎ𝑟

48. The enthalpy balance of the system can be given as per following
expression:
q = msλs = (mf−mp) Hv− mfHf + mp H
Hv= Specific enthalpy of vapour
Hf= specific enthalpy of thin liquor
H = specific enthalpy of thick liquor

49. Conclusion:
• Food engineering operations convert raw
agricultural commodities into canned, frozen,
dehydrated, formulated and otherwise
modified forms of food
• The main aim of food processing is
preservation of food materials.
• It also improve quality, texture, structure,
flavours and taste of the food commodities.

50. Thank You
Question & Suggestion