Unit Operation

Unit Operations
Semester 2 - 2010
Quality Technology – VBP045
Unit Operations
What do we mean by
“Unit Operations”?
Unit Operations
“Unit Operations” =
A food processing operation by
which raw materials are the
input and the desired product is
the output
Unit Operations
Using a material balance and an energy
balance, a food engineering process
can be viewed overall or as a series of
Each unit is a unit operation. The unit
operation can be represented by a box
as shown in Fig. 1.1.
View of a Unit Process
Unit Operations - Overview
Important unit operations in the food industry
 Heat transfer – thermal processing, freezing,
 Drying – dehydration and concentration
 Evaporation
 Contact equilibrium processes (which include
distillation, extraction, gas absorption,
crystallization, and membrane processes)
Important Unit Operations (cont)
 Mechanical separations (which include
filtration, centrifugation, sedimentation
and sieving)
 Size reduction – grinding, milling
 Mixing, forming and shaping
 Extrusion
Unit Operations
 Examples – what type of process
or processes are used in the
manufacture of examples
handed around in class?
 List and discuss on whiteboard
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
 “What goes in must come out".
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.
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
Examples of Unit Operations
2. Drying =
 Spray dried milk powder
 Sun dried tomatoes
 Freeze dried vegetables
 Pastas
Air drying, freeze drying, vaccum drying
Examples of Unit Operations
3. Evaporation =
Concentrated tomato paste
Evaporated milk
Concentrated fruit juices
Condensed soups
Examples of Unit Operations
4. Contact equilibrium processes =
Crystallisation – sugar, salt
Extraction – oils
Ultra-filtration of milks
Distillation of mixtures containing
alcohol, vinegars
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
Examples of Unit Operations
6. Size reduction =
 Grinding of sugar
 Crystallization of salt
 Grinding & milling of herbs and spices
Examples of Unit Operations
7. Mixing, forming, shaping =
 Using blenders to combine
 Soup mixes – blends of starch, vegies
 Blending – flavours for potato chips
 Premixes of flavourings for sausages
Examples of Unit Operations
8. Extrusion =
 Puffed corn, rice or other cereal
 “Cruskits”
 Corn thins
 Pasta shapes
Examples of Unit Operations
 Using the examples given, revise your
list of which “process” you think would
be used in to manufacture the foods.
 Discuss as a group
 Contact with
–Plate freezers
Vertical Plate Freezer
Contact Plate Freezer
 Contact with Liquid
–Liquid brine
–Synthetic coolant
Immersion freezer
 The immersion freezer consists of a
tank with a cooled freezing media, such
as glycol, glycerol, sodium chloride,
calcium chloride, and mixtures of salt
and sugar.
 The product is immersed in this
solution or sprayed while being
conveyed through the freezer
Contact with Liquid
Immersion freezing
Contact with gas
Blast freezer
Fluidized bed
Contact with Gas
 Blast Freezer
Tunnel Freezer
Spiral Blast Freezer
Fluidized bed Freezing
Cryogenic Freezing
 Liquid nitrogen, with a boiling
temperature of -196 °C at atmospheric
 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
Cryogenic tunnel
It’s a blast – Chilling and
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