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
