Homogenization

Milk is an oil-in-water type emulsion in which the butter fat is dispersed as fat globules in the skim milk portion. The greater part of the fat volume consists of globules with a diameter ranging from 2 to 6 μm. A few fat globules may exist which have a diameter of 10 μm. Milk fat contains also a large number of small fat globules with diameters down to 0.1 μm, but this do not greatly increase the total volume of the fat. 

Homogenization primarily causes disruption of fat globules into much smaller ones. Consequently, it diminishes creaming and may also diminish the tendency of globules to clump or coalesce. Essentially, all homogenized milk is produced by mechanical means.

Definition of Homogenized Milk

Homogenized milk is milk which has been treated in such manner as to ensure break-up of the fat globules to such an extent that after 48 hours of quiescent storage no visible cream separation occurs in the milk and the fat percentage of the milk in the top 100 ml of milk in a quart bottle (946ml), or of the proportionate volumes in containers of other sizes, does not differ by more than 10 per cent of itself from the fat percentage of the remaining milk as determined after thorough mixing.

Theories of Homogenization

The principle underlying the process of homogenization is to subject the fat globule to enough severe conditions, which disrupts it into smaller globules. This disruption, decreases the average diameter of fat globules, increases their number and total surface area. The newly formed fat globules are maintained in dispersion for sufficient time to allow milk fat globule membrane (MFGM) to be reformed at the fat-serum interface with casein and whey proteins. 

The following theories/mechanisms/forces have been proposed to be responsible for the entire phenomenon.

Shearing or Grinding

Exploding

Splashing/Shattering

Acceleration and Deceleration

Turbulence

Cavitation

Advantages and Disadvantages of Homogenized Milk

Advantages

•  Prevents removal of fat/cream from milk.

•  Homogenized milk results in softer curd and therefore easily digested by infants.

•  Churning of fat does not occur during bulk transportation.

•  Fat is uniformly distributed and therefore gives uniform consistency.

•  Homogenized milk is comparatively resistant to development of oxidized flavour defect.

Disadvantages

•  Homogenization offers possibility of incorporation of foreign fat into milk.

•  Homogenized milk is prone to development of ‘sunlight’ or ‘activated’ flavour defect.

•  Fat separation from homogenized milk is not possible if required.