Skim of low-fat milk processing

Dry milk was referred to as milk powder until the mid 1960s, when the designation was changed by the American Dry Milk Institute to dry milk in the United States.

Large quantities of skim of low fat milk are dried. This may be done by spraying atomized droplets of milk into chamber through which heated air is circulated (spray drying).

The atomizers used in this process include mainly rotary and pressure types. The final articles size of the dried powder produced by utilizing a rotary atomizer and the basic plant is greater than 1000 microns.

The milk also may dry by allowing it to flow over the surface of two heated metal drum that rotate toward each other.

A thin layer or film of product is dried over an internally steam-heated drum with steam pressure up to 620 kPa and 149 °C. Approximately 1.2 – 1.3 kg steam are required per kilogram of water evaporated.

The dried milk then is scraped from the drum surface, as they rotate, by metal scraper.

The operating variables for a drum dryer include condensation of incoming product in an elevator, temperature of incoming product, steam pressure in drum, speed of drum, and height of product over drum.

Dried milk (usually the spray dried type that contains about 5% of moisture) may be re-humidified to slightly higher moisture content after drying.

It has poor dissolving properties and where sold for domestic use is subjected to further instantisation, which agglomerates granules and leads to a faster dissolution time.
Skim of low-fat milk processing 

Spray drying of milk

Dried milk is manufactured from evaporated milk. In spray drying, the milk concentrate is finely dispersed in the spray tower by centrifugal atomization or by nozzle atomization and dried with hot air (150-220 °C). The final drying process reduces the water content to about 4%.

The removal of water by spray drying is an energy expensive process and even if it were not, spray drying would not normally be chosen as the only methods of water removal in milk powder production.

Spray dried powder consists of small, regular spherical particles, is light in color and had very little burnt taste.

In general, there are four stages in spray drying of drying milk powder, these are:
*Atomization of milk into a spray, at the top of the atomizing chamber
*Spray-air contact, mixing and flow
*Drying of spray droplets in flight
*Collection and separation process of milk powder from the air

Spray dried powder is generally considered to be of better organoleptic quality than roller dried.

Spray dried milk has poor dissolving properties and subjected to a further process, instantisation which agglomerates granules and leads to a faster dissolution time.
Spray drying of milk