Drum drying is a method used for drying out liquids; for example, milk 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 made by drum drying tends to have a cooked flavor, due to caramelization caused by greater heat exposure.
Compared to spray drying, 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 results in better quality milk powder.
Other products where drumdrying can be used are for example starches, breakfast cereals, baby food, instant mashed potatoes to make them cold water soluble.