Butter is made from cream or full-cream milk. Milk is basically water with tiny fat globules suspended in it. The fat is a pale yellow and gives the milk its colour.

To make butter, the milk is turned over and over, or churned, so that the tiny globules of butterfat clump together and so separate out from the watery liquid, or buttermilk. The fatty solid, which also contains proteins and a little water, can then be patted together to make a block of butter.

Salt is often added to butter to bring out the flavour and to preserve it.

Butter has the advantage of being soft at room temperatures, although it melts when the temperature reaches about 32°C/ 90F. The density of butter is 911 g/L (56.9 lb/ft3).

Most of us are used to milk which has been changed so that the fat is evenly spread through the liquid. But natural milk has larger globules of fat, and if left, these rise to the surface to make cream. But the fat (cream) globules are still separate from one another, which is why it remains a liquid. However, if the cream is stirred quickly, the fat will eventually come together into larger globules, and the water can be drained off (this is buttermilk). The fat can then be patted into a block. Butter is about four fifths fat, and has a higher fat content than cheese.

Butter is mostly made from pasteurised milk. This means that it will keep for several months, whereas butter made in a traditional way using unpasteurised milk lasts for only about 10 days. The butter flavour comes from 'souring' the cream, which is produced by growing bacteria in the butter, that is by fermenting it. Butter is slightly fermented milk, whereas cheese is milk that is much more fermented.

Butter has an interesting history. Today it is thought of as something of a luxury product. However, for thousands of years it was thought of as the food of peasants, and was not eaten by the wealthy. It was even used as a fuel for oil lamps when other kinds of oil were in short supply. Butter started to be eaten by the wealthy when it was allowed as a food during Lent

The first butter substitute was margarine. It was invented in France in 1869 and made of beef tallow flavoured with milk. Later vegetable margarines were developed.

Some people now worry about using butter because they think it is fattening and because it contains animal fats which, some argue, will cause more cholesterol in the blood, and increase the chances of heart attack. However, more recent research has shown this is unlikely to be the case, which is why sales of butter have gone up again. . Butter is a good source of Vitamin A.

It is possible to make butter at home using an electrical food mixer. Start with the thickest cream you can buy (called thick cream, whipping cream, heavy cream or something like that) and whisk it at high speed until the fat separates from the liquid. The nearly solid cream can then be worked into blocks of butter by hand. If you don't have a whisk, then put very thick cream into a clear class jar with a screw top. Put about half a jar's worth of cream in, then shake the jar until the buttermilk separates from the solid butter. Pour off (and use) the buttermilk, and pat the butter into a block and spread it onto bread or crackers. This is unsalted butter, of course. Compare your butter to shop-made unsalted butter, and also salted butter. Salt is a preservative as well as bringing out the flavour. This is a fun experiment to do in class if everyone brings in a clean jam jar.