Dried Dairy Products

Milk Powder

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:

  1. contains less milkfat (0.05-0.10%)
  2. heat treatment prior to evaporation can be more or less severe
  3. homogenization not required
  4. 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.

Whey Powder

Whey is the by-product in the manufacturing of cheese and casein. Disposing of this whey has long been a problem. For environmental reasons it cannot be discharged into lakes and rivers; for economical reasons it is not desirable to simply dump it to waste treatment facilities. Converting whey into powder has led to a number products that it can be incorporated into. It is most desirable, if and where possible, to use it for human food, as it contains a small but valuable protein component. It is also feasible to use it as animal feed. Between the pet food industry and animal feed mixers, hundred's of millions of pounds are sold every year. The feed industry may be the largest consumer of dried whey and whey products.

Whey powder is essentially produced by the same method as other milk powders. Reverse osmosis can be used to partially concentrate the whey prior to vacuum evaporation. Before the whey concentrate is spray dried, lactose crystallization is induced to decrease the hygroscopicity. This is accomplished by quick cooling in flash coolers after evaporation. Crystallization continues in agitated tanks for 4 to 24 h.

fluidized bed may be used to produce large agglomerated particles with free-flowing, non-hygroscopic, no caking characteristics.

Whey Protein Concentrates

Both whey disposal problems and high-quality animal protein shortages have increased world-wide interest in whey protein concentrates. After clarification and pasteurization, the whey is cooled and held to stabilize the calcium phosphate complex, which later decreases membrane fouling. The whey is commonly processed using ultrafiltration, although reverse osmosis, microfiltration, and demineralization methods can be used. During ultrafiltration, the low molecular weight compounds such as lactose, minerals, vitamins and nonprotein nitrogen are removed in the permeate while the proteins become concentrated in the retentate. After ultrafiltration, the retentate is pasteurized, may be evaporated, then dried. Drying, usually spray drying, is done at lower temperatures than for milk in order that large amounts of protein denaturation may be avoided.