Cheese is made from milk. Milk is a complicated mixture of natural substances that we get mainly from cows, buffalo, goats, or sheep. Although milk looks like just one thing, if you were able to look at it very closely, for example under a microscope, you would find that it is made of tiny globules of fat suspended (not dissolved) in a slightly yellowish runny liquid. The runny liquid is mostly water, but it also contains many other valuable things, among which is a body-building substance called protein as well as lots of sugar.

Cheese is made from just the fat and protein part of this milk. That is why much of the cheese is fat. The rest is one special protein from the milk called casein.

To make cheese, the water has to be removed and the proteins have be made to clump the fat globules together – something called curdling (coagulating). Of course, natural milk contains substances to prevent this happening, so the milk has to be treated. First it is made slightly acid. This may be by adding, for example, a little vinegar or lemon juice. More commonly it is by allowing bacteria to grow in the milk. As they do this, the bacteria change the sugars in the milk into an acid (called lactic acid). Some of these bacteria also produce bubbles of carbon dioxide gas. This is what gives the holes in some cheeses.

Then a special substance called rennet is added, which causes the proteins to group the fats together. Rennet is an animal product from the lining of a sheep's stomach; vegetarians use a fungus alternative.

During all of this time, the milk is stirred and slightly warmed. This means the rennet and bacteria reach all parts of the milk, and the warming makes all the changes happen more quickly. Eventually, rennet sets the cheese into a strong and rubbery gel. Without it what would be produced is fragile lumpy curds. Rennet also allows curdling to happen while the milk is only slightly acid. This is important because flavour-making bacteria cannot live in liquids that are too acid. Now you can also see how we can get two quite different kinds of cheese: soft fresh cheeses like cottage cheese are curdled with more acid to rennet, while harder longer-aged cheeses like cheddar have less acid and more rennet.

For more videos on various cheeses, and food in general, go to the museum tab on the home screen.

We also have many cheese videos in the food part of the website. The video below is just one of them. Use the Jump-to link at the foot of this page to see them.