Spray drying of milk

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.

Drying be done by spraying atomized droplets of milk into chamber through which heated air is circulated (spray drying).

Milk to be spray dried should receive at least a minimum temperature pasteurization before evaporation and further processing, though higher temperature heat treatments are commonly used in order to influence product characteristics.

In the more modern and more widely used process, concentrated milk is sprayed through an atomizer into the top of a large chamber with air at 120 – 205 °C blown in from the base. The particles dry rapidly and are collected at the bottom of the chamber.

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

This treatment agglomerates the fine milk particles  to form clumps of milk powder, which results in a powder that dissolves or disperses in water much more rapidly that the finely powdered dried milk. It is therefore, considered to be an instantly double product.

Original spray dryer designs were for single stage drying in which all of the moisture is removed in the main drying chamber. Such designs are now obsolescent and have been replaced by two and three stage dryers in which the drying process is completed in fluidized bed dryers.
Spray drying of milk