unit operations

1. Unit Operations
What do we mean by
“Unit Operations”?

2. Unit Operations
“Unit Operations” =
A food processing operation by
which raw materials are the
input and the desired product is
the output

3. View of a Unit Process

4. Unit Operations - Overview
Important unit operations in the food industry
are:
▪ Heat transfer – thermal processing, freezing,
chilling
▪ Drying – dehydration and concentration
▪ Evaporation
▪ Contact equilibrium processes (which include
distillation, extraction, gas absorption,
crystallization, and membrane processes)

5. Important Unit Operations (cont)
▪ Mechanical separations (which include
filtration, centrifugation, sedimentation
and sieving)
▪ Size reduction – grinding, milling
▪ Mixing, forming and shaping
▪ Extrusion

6. Mass & Energy
▪ Two very important laws which all unit
operations obey are the laws of
conservation of mass and energy.
▪ The law of conservation of mass states
that mass can neither be created nor
destroyed.
▪ “What goes in must come out".

7. Mass & Energy
▪ The law of conservation of energy
states that energy can neither be
created nor destroyed. The total energy
in the materials entering the processing
plant, plus the energy added in the
plant, must equal the total energy
leaving the plant.

8. Examples of Unit Operations
1. Heat Transfer =
▪
▪
▪
▪
▪
▪
Pasteurisation of milk
Freezing of fish
Ultra heat treatment (UHT) of juice
Chilling meat patties/burgers
Steam jacketed kettle used to sauces
Canned fruits

9. Examples of Unit Operations
2. Drying =
▪
▪
▪
▪
Spray dried milk powder
Sun dried tomatoes
Freeze dried vegetables
Pastas
Types:
Air drying, freeze drying, vaccum drying

10. Examples of Unit Operations
3. Evaporation =
▪
▪
▪
▪
Concentrated tomato paste
Evaporated milk
Concentrated fruit juices
Condensed soups

11. Examples of Unit Operations
4. Contact equilibrium processes =
▪
▪
▪
▪
Crystallisation – sugar, salt
Extraction – oils
Ultra-filtration of milks
Distillation of mixtures containing
alcohol, vinegars

12. Examples of Unit Operations
5. Mechanical separations =
▪
▪
▪
▪
Centrifuging – cream, butter
Separation of oil and water eg.
Filtration – of oils using a press
Sieving – flours, cereals, grains

13. Examples of Unit Operations
6. Size reduction =
▪
▪
▪
Grinding of sugar
Crystallization of salt
Grinding & milling of herbs and spices

14. Examples of Unit Operations
7. Mixing, forming, shaping =
▪ Using blenders to combine
ingredients
▪ Soup mixes – blends of starch, vegies
▪ Blending – flavours for potato chips
▪ Premixes of flavourings for sausages

15. Examples of Unit Operations
8. Extrusion =
▪ Puffed corn, rice or other cereal
products
▪ “Cruskits”
▪ Corn thins
▪ Pasta shapes

16. Cryogenic Freezing
▪ Liquid nitrogen, with a boiling
temperature of -196 °C at atmospheric
pressure
▪ Liquid carbon dioxide the gas is
released to the atmosphere at -70 °C,
half of the gas becomes dry-ice snow
and the other half stays in the form of
vapor.