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 units. 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 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)
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 destroyed. “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 Types: 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 ingredients 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 products “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
Freezing 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
Freezing Contact with gas Blast freezer Fluidized bed
Contact with Gas Blast Freezer
Spiral Blast Freezer
Fluidized bed Freezing
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.