CBSE Class 8 Answered

In modern times, powdered milk is usually made by spray drying or drum drying. Milk is evaporated to a certain degree and then dried by either roller drying by a roller dryer or spray drying in a spray dryer.

In roller drying, steam is injected inside a rotating drum dryer. As the milk evaporates, the partially evaporated milk is injected onto the outer surface of the dryer. As the dryer rotates, the moisture from the milk gets removed. The dried milk is then removed from the dryer surface with a blade attached to the dryer. The dried milk falls on a conveyor belt and removed.

In spray drying, partially evaporated milk is sprayed in very fine droplets from the top of the dryer. A hot air is blown under pressure inside the drying chamber. As soon as the droplets come in contact with the hot air, moisture from the droplets just evaporates and the dried powder drools down the bottom and removed by a conveyor belt.