There are basically two methods of pasteurization in use today: Batch In the batch process (batch pasteurizer, right) , a large quantity of milk is held in a heated vat at 65°C for 30 minutes, followed by quick cooling to about 4°C. continuous flow In the continuous flow process (continuous flow pasteurizer, below, right)-also known as HTST, for high temperature, short time, milk is forced between metal plates or through pipes heated on the outside by hot water. While flowing under pressure, the milk is held at 72°C for at least 16 seconds. Before being chilled back to 4°C or cooler, it flows through a heat exchanger to pre-warm cold milk just entering the system.