unit operations in food engineering

1. Unit OperationsUnit Operations
P C VengaiahP C Vengaiah

2. Unit OperationsUnit Operations
What do we mean byWhat do we mean by
““Unit Operations”?Unit Operations”?

3. Unit OperationsUnit Operations
““Unit Operations” =Unit Operations” =
AA food processingfood processing operation byoperation by
which raw materials are thewhich raw materials are the
input and the desired product isinput and the desired product is
the outputthe output

4. Unit OperationsUnit Operations
Using a material balance and an energyUsing a material balance and an energy
balance, a food engineering processbalance, a food engineering process
can be viewed overall or as a series ofcan be viewed overall or as a series of
units.units.
Each unit is a unit operation. The unitEach unit is a unit operation. The unit
operation can be represented by a boxoperation can be represented by a box
as shown inas shown in Fig. 1.1Fig. 1.1..

5. View of a Unit ProcessView of a Unit Process

6. Unit Operations - OverviewUnit Operations - Overview
Important unit operations in the food industryImportant unit operations in the food industry
are:are:
 Heat transfer – thermal processing, freezing,Heat transfer – thermal processing, freezing,
chillingchilling
 Drying – dehydration and concentrationDrying – dehydration and concentration
 EvaporationEvaporation
 Contact equilibrium processes (which includeContact equilibrium processes (which include
distillation, extraction, gas absorption,distillation, extraction, gas absorption,
crystallization, and membrane processes)crystallization, and membrane processes)

7. Important Unit Operations (cont)Important Unit Operations (cont)
 Mechanical separations (which includeMechanical separations (which include
filtration, centrifugation, sedimentationfiltration, centrifugation, sedimentation
and sieving)and sieving)
 Size reduction – grinding, millingSize reduction – grinding, milling
 Mixing, forming and shapingMixing, forming and shaping
 ExtrusionExtrusion

8. Unit OperationsUnit Operations
 Examples – what type of processExamples – what type of process
or processes are used in theor processes are used in the
manufacture of examplesmanufacture of examples
handed around in class?handed around in class?

9. Mass & EnergyMass & Energy
 Two very important laws which all unitTwo very important laws which all unit
operations obey are the laws ofoperations obey are the laws of
conservation of mass and energy.conservation of mass and energy.
 The law ofThe law of conservation of massconservation of mass statesstates
that mass can neither be created northat mass can neither be created nor
destroyed.destroyed.
 ““What goes in must come out".What goes in must come out".

10. Mass & EnergyMass & Energy
 The law ofThe law of conservation of energyconservation of energy
states that energy can neither bestates that energy can neither be
created nor destroyed. The total energycreated nor destroyed. The total energy
in the materials entering the processingin the materials entering the processing
plant, plus the energy added in theplant, plus the energy added in the
plant, must equal the total energyplant, must equal the total energy
leaving the plant.leaving the plant.

11. Examples of Unit OperationsExamples of Unit Operations
1.1. Heat TransferHeat Transfer ==
 Pasteurisation of milkPasteurisation of milk
 Freezing of fishFreezing of fish
 Ultra heat treatment (UHT) of juiceUltra heat treatment (UHT) of juice
 Chilling meat patties/burgersChilling meat patties/burgers
 Steam jacketed kettle used to saucesSteam jacketed kettle used to sauces
 Canned fruitsCanned fruits

12. Examples of Unit OperationsExamples of Unit Operations
2.2. DryingDrying ==
 Spray dried milk powderSpray dried milk powder
 Sun dried tomatoesSun dried tomatoes
 Freeze dried vegetablesFreeze dried vegetables
 PastasPastas
Types:Types:
Air drying, freeze drying, vaccum dryingAir drying, freeze drying, vaccum drying

13. Examples of Unit OperationsExamples of Unit Operations
3.3. EvaporationEvaporation ==
 Concentrated tomato pasteConcentrated tomato paste
 Evaporated milkEvaporated milk
 Concentrated fruit juicesConcentrated fruit juices
 Condensed soupsCondensed soups

14. Examples of Unit OperationsExamples of Unit Operations
4.4. Contact equilibrium processesContact equilibrium processes ==
 Crystallisation – sugar, saltCrystallisation – sugar, salt
 Extraction – oilsExtraction – oils
 Ultra-filtration of milksUltra-filtration of milks
 Distillation of mixtures containingDistillation of mixtures containing
alcohol, vinegarsalcohol, vinegars

15. Examples of Unit OperationsExamples of Unit Operations
5.5. Mechanical separationsMechanical separations ==
 Centrifuging – cream, butterCentrifuging – cream, butter
 Separation of oil and water eg.Separation of oil and water eg.
 Filtration – of oils using a pressFiltration – of oils using a press
 Sieving – flours, cereals, grainsSieving – flours, cereals, grains

16. Examples of Unit OperationsExamples of Unit Operations
6.6. Size reductionSize reduction ==
 Grinding of sugarGrinding of sugar
 Crystallization of saltCrystallization of salt
 Grinding & milling of herbs and spicesGrinding & milling of herbs and spices

17. Examples of Unit OperationsExamples of Unit Operations
7.7. Mixing, forming, shapingMixing, forming, shaping ==
 Using blenders to combineUsing blenders to combine
ingredientsingredients
 Soup mixes – blends of starch, vegiesSoup mixes – blends of starch, vegies
 Blending – flavours for potato chipsBlending – flavours for potato chips
 Premixes of flavourings for sausagesPremixes of flavourings for sausages

18. Examples of Unit OperationsExamples of Unit Operations
8.8. ExtrusionExtrusion ==
 Puffed corn, rice or other cerealPuffed corn, rice or other cereal
productsproducts
 ““Cruskits”Cruskits”
 Corn thinsCorn thins
 Pasta shapesPasta shapes

19. Examples of Unit OperationsExamples of Unit Operations
 Using the examples given, revise yourUsing the examples given, revise your
list of which “process” you think wouldlist of which “process” you think would
be used in to manufacture the foods.be used in to manufacture the foods.

20. FreezingFreezing
 Contact withContact with
solidsolid
–Plate freezersPlate freezers
VerticalVertical
HorizontalHorizontal
Contact Plate FreezerContact Plate Freezer
Vertical Plate FreezerVertical Plate Freezer

22. FreezingFreezing
 Contact with LiquidContact with Liquid
–Liquid brineLiquid brine
–Synthetic coolantSynthetic coolant

23. Immersion freezerImmersion freezer
 The immersion freezer consists of aThe immersion freezer consists of a
tank with a cooled freezing media, suchtank with a cooled freezing media, such
as glycol, glycerol, sodium chloride,as glycol, glycerol, sodium chloride,
calcium chloride, and mixtures of saltcalcium chloride, and mixtures of salt
and sugar.and sugar.
 The product is immersed in thisThe product is immersed in this
solution or sprayed while beingsolution or sprayed while being
conveyed through the freezerconveyed through the freezer

24. Contact with LiquidContact with Liquid
Immersion freezingImmersion freezing

25. FreezingFreezing
Contact with gasContact with gas
Blast freezerBlast freezer
Fluidized bedFluidized bed

26. Contact with GasContact with Gas
 Blast FreezerBlast Freezer

27. Tunnel FreezerTunnel Freezer

28. Spiral Blast FreezerSpiral Blast Freezer

29. Fluidized bed FreezingFluidized bed Freezing

30. Cryogenic FreezingCryogenic Freezing
 Liquid nitrogen, with a boilingLiquid nitrogen, with a boiling
temperature of -196 °C at atmospherictemperature of -196 °C at atmospheric
pressurepressure
 Liquid carbon dioxide the gas isLiquid carbon dioxide the gas is
released to the atmosphere at -70 °C,released to the atmosphere at -70 °C,
half of the gas becomes dry-ice snowhalf of the gas becomes dry-ice snow
and the other half stays in the form ofand the other half stays in the form of
vapor.vapor.

31. Cryogenic tunnelCryogenic tunnel