Unit Operations in Food Processing

—Series of physical processes that can be broken down into simple operations are considered as Unit Operations

—These operations can stand alone

*Unit Operations –

—Material Handling



—Size reduction

—Fluid Flow


—Heat transfer






* Materials Handling –

  • Includes
    Harvesting, refrigerated trucking of perishable produce, transportation of live animals, conveying a product from truck or rail car to storage
  • During these operations
    Sanitary conditions must be maintained
    Losses minimized
    Quality maintained
    Bacterial growth minimized
  • Transfers and deliveries must be on time while keeping time to a minimum for efficiency and quality
  • Trucks, trailers, harvesting equipment, rail cars , a variety of conveyors, forklifts, storage bins, & pneumatic lift systems are all part of the process

* Cleaning –

  • Ranges from dirt removal to the removal of bacteria from liquids
  • Uses
    High-velocity air
    Micro filtration
    Mechanical separation
  • Method used depends on the food surface
  • Equipment and floors and walls of the facility also require frequent, thorough cleanings to maintain product quality

*Separating –

  • Achieved on the basis of density or size and shape
  • Density based separations include
    Cream from milk
    Solids from suspension
    Removal of bacteria from fluid

*Size Reduction –

  • Uses high-shear forces, grater, cutters, slicers, homogenizers, ball mill grinders
    Size reducers used for meat include
  • Grinders, Bacon slicers, sausage stuffers, & vertical choppers
  • Better thought of as size adjustment because size can be reduced or it can be increased by aggregation, agglomeration or gelation

*Pumping (Fluid Flow) –

  • Achieved by either gravity flow or through the use of pumps
    Gravity flow
    Flow is laminar and is transferred from the fluid to the wall between the adjacent layers
    Adjacent molecules don’t mix
    Centrifugal pump uses a rotating impeller to create a centrifugal force within the pump cavity. The flow is controlled by the choice of the impeller diameter and rotary speed of the pump drive. The capacity of a centrifugal pump is dependent upon the speed, impeller length and the inlet and outlet diameters
    Positive Pumps consist of a reciprocating or rotating cavity between two lobes or gears and a rotor. Fluid enters by gravity or a difference in pressure, and the fluid forms the seals between the rotating parts. The rotating movement of the rotor produces the pressure to cause the fluid to flow.

* Mixing –

  • Two major purposes
    Heat transfer
    Ingredient incorporation
  • Different mixer configurations are used to achieve different purposes
  • Efficiency depends on
    Design of impeller
    Diameter of impeller

* Heat Exchange –

  • Used for either heating or cooling
  • Used to
    Destroy microorganisms, produce a healthful food, prolong shelf-life through destruction of enzymes and to promote products with acceptable taste, odor and appearance

*Concentration –

  • Achieved through evaporation and reverse osmosis
  • Often used a pre-step to drying to reduce costs

*Drying –

  • In this operation volatile liquid, usually water, are removed from solid materials.
  • 3 methods
    Sun or tray

* Forming –

  • Processes
    Powders & binding agents
    Heat and pressure
    Extrusion cooking
  • Used for
    Hamburger patties, chocolates
    Jellies, tablets, butter, sausages,
    Variety breads, margarine bars,

* Packaging –

  • Machines operate at high speeds and automatically package food products in a step-wise and automated fashion from forming the container, filling the container, sealing the container, labeling and stacking it
  • Use a variety of materials

* Controlling –



  • Tools include
    Other instruments to control pressure, temperature, fluid flow, acidity, weight, viscosity, humidity, time and specific gravity
  • All automated


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