Centrifugation in the Dairy Industry

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What is the primary purpose of clarification in centrifugation?

Removal of solid impurities from milk prior to pasteurization

What is the function of the discharge slots in a self-cleaning centrifuge bowl?

To allow ejection of sediment during continuous separation/clarification

Which phase moves towards the bowl wall in a centrifuge?

Dense phase

How many discs can be stacked together in a centrifuge?

Up to 120 discs

What is the result of self-cleaning in a centrifuge on milk processing?

Loss of 25 L/hr of milk for one dairy

Which process involves the separation of bacteria from milk in centrifugation?

Bactofuge treatment

What is the purpose of keeping the pasteurized milk at least 1 psi higher than raw milk in the regenerator?

To prevent contamination of pasteurized milk with raw milk in case of a pin-hole leak.

What is the function of the balance or constant level tank in an HTST pasteurizer?

It provides a constant milk supply.

Why must the overflow level be kept below the lowest milk passage in the regenerator?

To maintain a higher pressure on the pasteurized side of the heat exchanger.

How does the balance tank prevent air from entering the pasteurizer?

By creating a downward slope of at least 2% on the outlet pipe.

What is one of the functions of a regenerator in a pasteurizer?

Utilizes the heat content of pasteurized milk to warm incoming milk.

Why must the holding tube slope upwards in the direction of flow?

To eliminate air entrapment and ensure uniform flow velocity.

Which method of UHT processing involves heating by injecting steam directly into the product?

Injection heating

What is the primary function of homogenization in milk processing?

To create an oil-in-water emulsion

Which packaging method for aseptic processing involves erecting, sterilizing, filling, and sealing knocked-down blanks?

Erect, fill and seal

What is the primary drawback of a lack of equipment for particulate sterilization?

Settling of solids

In the context of UHT processing, what results in a more pronounced cooked flavor in milk?

Injection heating

What is a distinguishing feature of indirect heating systems used in UHT processing?

Scraped surface method

What is the primary purpose of pasteurization in milk and milk products?

Destroying harmful bacteria (pathogens)

Which method of pasteurization saves time and energy compared to the vat method?

Continuous method

What is commonly used as the heating medium in an HTST pasteurizer?


Which equipment is essential in an HTST pasteurizer to facilitate heat exchange?

Plate heat exchanger

For continuous pasteurizing, what is crucial to maintain in the heat exchanger?

Higher pressure on the pasteurized side

What is the holding time required for milk inside the heat exchanger during pasteurization at 72°C?

15 seconds

Study Notes

Centrifugation and Separation

  • Centrifugation is used in the dairy industry for clarification, skimming, standardizing, whey separation, bactofuge treatment, quark separation, and butter oil purification.
  • Centrifuges can separate and clarify at the same time, with dense particles thrown to the perimeter, forming solids that collect in the centrifuge.
  • Modern self-cleaning centrifuges allow for continuous separation/clarification, with a specially constructed bowl that can eject 8 to 25 L of sediment every 60 min.

Centrifuge Components

  • A centrifuge consists of up to 120 discs stacked together at a 45 to 60 degree angle.
  • Milk is introduced towards the inner edge of the disc stack through vertically aligned distribution holes.
  • Dense phase moves towards the bowl wall, along the underside of the discs, while light phase moves towards the center, along the upper faces of the discs.

HTST Pasteurizer Components

  • Balance tank provides a constant milk supply, with a float valve assembly controlling the liquid level.
  • Regenerator utilizes the heat content of pasteurized milk to warm the incoming milk.
  • Timing pump draws product through the raw regenerator and pushes milk under pressure through the pasteurized regenerator.
  • Holding tube must slope upwards 1/4″/ft in direction of flow to eliminate air entrapment.
  • Indicating thermometer is the most accurate temperature measurement.


  • Pasteurization is used to make milk and milk products safe for human consumption by destroying all bacteria that may be harmful to health (pathogens).
  • It improves the keeping quality of milk and milk products, destroying some undesirable enzymes and many spoilage bacteria.
  • Shelf life can be 7, 10, 14, or up to 16 days.

Pasteurization Methods

  • Batch method: milk is heated to 63°C for 30 min, then cooled to 4°C.
  • Continuous process method: saves time and energy compared to the vat method, using a high temperature short time (HTST) pasteurizer with a plate heat exchanger.
  • HTST pasteurizer maintains a higher pressure on the pasteurized side of the heat exchanger, with a holding time of 15s at 72°C.

UHT Methods

  • Direct heating systems: injection, infusion
  • Indirect heating systems: plate, tubular, scraped surface

Packaging for Aseptic Processing

  • Fill and seal: preformed containers made of thermoformed plastic, glass, or metal are sterilized, filled in aseptic environment, and sealed.
  • Form, fill, and seal: roll of material is sterilized, formed in a sterile environment, filled, and sealed.
  • Erect, fill, and seal: using knocked-down blanks, erected, sterilized, filled, and sealed.
  • Thermoform, fill, and seal: roll stock sterilized, thermoformed, filled, and sealed aseptically.
  • Blow mold, fill, and seal


  • Homogenization is a mechanical treatment of the fat globules in milk, achieved by passing milk under high pressure through a tiny orifice.
  • Milk is an oil-in-water emulsion, with fat globules dispersed in a continuous skim milk phase.

Explore the process of centrifugal separation in the dairy industry, including its various uses such as clarification, skimming, whey separation, bactofuge treatment, quark separation, and butter oil purification. Test your knowledge on this essential technique for dairy production.

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