Cooling or refrigeration is the process of removing thermal energy from a system or object.

Usually this makes solids out of liquids or suspensions. Drum dryers are best suited to applications such as these.

Here, pastes or liquid substances are applied onto a roller (e. g. liquid wax). The cooled roller removes the heat from the product so that the product changes in state and becomes solid again. After a ¾ turn, the product is shaved or scaled off. This is also referred to as a scaler roller.