Skimmed milk powder is a dairy product made by evaporating skimmed milk until it is completely dry. This powder is easier to store and transport than skimmed milk in liquid form, and it is typically less expensive. Skimmed milk powder is widely used in food manufacture, and it is often included by humanitarian agencies in famine relief shipments. Powdered skim milk is also available in supermarkets for home use.
Making the powder begins with pasteurizing whole milk and removing the cream to make skimmed milk, just like what is typically found in the chilled dairy aisle of a grocery store. Milk is then run through a drying process until it dries to a white powder. Spray drying and drum drying are the most common evaporation methods, but freeze drying is also an option.
Spray drying works by running pasteurized skimmed milk in an evaporator to concentrate it, until it contains roughly 50% milk solids. Concentrated milk is then sprayed into a heated chamber. Evaporation occurs nearly instantly, leaving the solids as a heavy white powder. This is the most common method of drying milk.
Drum drying makes use of a heated drum to evaporate the milk. As the drum rolls, the liquid inside clings to the heated surface, forming a thin film. Heat evaporates the water, leaving only the solids. Skimmed milk powder made in a drum tends to have a distinct cooked flavor, however, which makes it less popular than the spray dried variety.
Powdered skimmed milk is classified based on the temperatures used in the evaporation process. High heat skimmed milk powder is the least soluble, and is most often used in recipes for baking. Low heat powder is the most suitable for reconstituting into milk for drinking and for general home use.
Milk can be reconstituted by adding water. To make 1 cup (700 ml) for drinking, add 3 tablespoons (45 ml) of skimmed milk powder to 1 cup (700 ml) of water. This should be mixed thoroughly before drinking, stirring or shaking vigorously. Making it well ahead of time is preferred, giving the powder more time to dissolve thoroughly. Even then, reconstituted skimmed milk does not taste like that which is packaged in liquid form, and many do not care for the taste, preferring to use the powder exclusively for cooking.
Nonfat dry milk is very similar to skimmed milk powder, with each containing no more than 5% water and 1.5% milkfat by weight. Powdered skim milk must contain at least 34% milk protein. Nonfat dry milk has no specified milk protein content.