Drum drying is a method used for drying out liquids; for example, milk

Milk

Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

 is applied as a thin film to the surface of a heated drum, and the dried milk solids are then scraped off with a knife. Powdered milk

Powdered milk

Powdered milk is a manufactured dairy product made by evaporating milk to dryness. One purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for...

 made by drum drying tends to have a cooked flavor, due to caramelization caused by greater heat exposure.

Compared to spray drying

Spray drying

Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some...

, drum drying is a more intense heat treatment which results in more denatured proteins. The powder is less soluble as a result. The temperature uniformity of the heated roller/drum is poor so spray drying

Spray drying

Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some...

 results in better quality milk powder.

Other products where drumdrying can be used are for example starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

es, breakfast cereals, baby food

Baby food

Baby food is any food, other than breastmilk or infant formula, that is made specifically for infants, roughly between the ages of four to six months to 2 years. The food comes in multiple varieties and tastes, can be produced by many manufacturers, or may be table food that the rest of the family...

, instant mashed potatoes to make them cold water soluble.