Unit operation

 Unit Operations

---

---

What do we mean by  "Unit Operations"?

 

Unit Operations "Unit Operations" = A food Processing operation  

which raw materials are the input and the desired product is the output 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. The unit operation can be represented by a box as shown in Fig. 1.1.

 

 

 

Unit Operation - Overview

History

Historically, the different chemical industries were regarded as different industrial processes and with different principles. Arthur Dehon Little developed the concept of "unit operations" to explain industrial chemistry processes in 1916.^[1] In 1923, William H. Walker, Warren K. Lewis and William H. McAdams wrote the book The Principles of Chemical Engineering and explained that the variety of chemical industries have processes which follow the same physical laws

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).

- Mechanical separations (which include filtration, centrifugation, sedimentation and sieving).

- Size reduction - grinding, milling.

- Mixing, forming and shaping.

- Extrusion.

- Examples - what type of process or processes are used in the manufacture of examples handed around in class?

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".

Principle

- The law of  energy states that energy can neither be created nor destroyed. The total enery in the materials entering added in the plant, must equal the total energy leaving the plant.

Types of unit operations

1. Heat Transfer

• Pasteurisation of milk
• Freezing of fish
• Ultra heat treatment of juice
• Chilling meat patties/burgers
• Steam jacketed kettle used to sauces
• Canned fruits

2. Drying

• Spary dried milk powder
• Sun dried tomatoes
• Freeze dried vegetables
• Pastas

3. Evaporation

 

• Concentrated tomato paste 
• Evaporated milk
• Concentrated fruit juices
• Condensed soups

4. Contact equilibrium processes

• Crystallisation- Sugar, salt
• Extraction- oils
• Ultra filtration of milks
• Distillation of mixtures containing alcohol, vinegars

5. Mechanical separations

 

• Centrifuging- cream, butter
• Separation of oil and water 
• Filtration- oils using a press
• Sieving- flours, cereals and grains

6. Size reduction

• Grinding of sugar
• Crystallization of salt
• Grinding and milling of herbs and spices

 

 

7. Mixing, forming, shaping

• Using blenders to combine ingredients
• Soup mixes- blends of starch, vegies
• Blending- flavours for potato chips
• Premixes of flavouring for sausages

8. Extrusion

 

•  Puffed corn, rice or other cereal products
• Cruskits
• Corn thins
• Pasta shapes