At home you can make ice-cream in the freezer or in an ice-cream maker but if you need to make thousands of litres a day, you need to use a different method.
This is what happens in an ice-cream factory:
First the ingredients are weighed out and mixed together.
Then the mix is pasteurised. This means it is heated to a high temperature to kill off any harmful bacteria.
The mix is also homogenised. This means breaking down the fat globules in the milk or cream to make them smaller. Now the ice-cream will be smoother, will whip better and won't melt as easily.
The mix is then left for at least four hours, usually overnight, to let the fat cool and form into crystals.
Any flavours, fruit purees, or colours are added at this point.
The mix is then pumped through a special barrel freezer which freezes some of the water in the ice-cream and whips air into it at the same time. Up to half the volume of ice-cream is air. Without it, the ice-cream would be like a frozen ice cube.
Any fruits, nuts, sweets or biscuit bits are added to the semi-frozen mixture at this point.
The ice cream is then packaged and put into a blast freezer at -30° to -40°C where more of the water in the ice-cream is frozen to make it harder.