Milk used in the production of milk powders is first clarified, standardized and then given a heat treatment. This heat treatment is usually more severe than that required for pasteurization. Besides destroying all the pathogenic and most of the spoilage microorganisms, it also inactivates the enzyme lipase which could cause lipolysis during storage.
The milk is then evaporated prior to drying for the following reasons:
- less occluded air and longer shelf life for the powder
- viscosity increase leads to larger powder particles
- less energy required to remove part of water by evaporation; more economical
Homogenization may be applied to decrease the free fat content. Spray drying is the most used method for producing milk powders. After drying, the powder must be packaged in containers able to provide protection from moisture, air, light, etc. Whole milk powder can then be stored for long periods (up to about 6 months) of time at ambient temperatures.
Skim milk powder (SMP) processing is similar to that described above except for the following points:
- contains less milkfat (0.05-0.10%)
- heat treatment prior to evaporation can be more or less severe
- homogenization not required
- maximum shelf life extended to approximately 3 years
Low-heat SMP is given a pasteurization heat treatment and is used in the production of cheese, baby foods etc. High-heat SMP requires a more intense heat treatment in addition to pasteurization. This product is used in the bakery industry, chocolate industry, and other foods where a high degree of protein denaturation is required.
Instant milk powder is produced by partially rehydrating the dried milk powder particles causing them to become sticky and agglomerate. The water is then removed by drying resulting in an increased amount of air incorporated between the powder particles.