How Does Milk Become Cheese?

Step 1 of 5

Milk is protein and fat floating in water.

Milk looks like one liquid but it is tiny bundles of protein and droplets of fat suspended in a lot of water. Cheese-making is the business of getting those bundles to clump together.

Step 2 of 5

Acid or rennet makes it split.

Add something acidic, or an enzyme called rennet, and the protein bundles stop repelling each other and stick together instead. The solid lumps are curds; the watery part left over is whey.

Step 3 of 5

Pressing decides how hard it will be.

The more whey squeezed out, the harder and longer-lasting the cheese. Barely pressed makes something soft you eat this week; pressed hard makes a block that keeps for a year.

Step 4 of 5

Salt does two jobs.

It draws out more water and it stops the wrong bacteria growing. That leaves only the ones the cheese-maker wants, quietly working away inside for months.

Step 5 of 5

Ageing is where the flavour comes from.

Fresh curd tastes of almost nothing. Over months, bacteria and moulds break the proteins and fats into hundreds of smaller compounds — and those are the sharp, nutty, tangy flavours.

Blue cheese is deliberately spiked with a mould and then pierced with needles, so air reaches the middle and the blue veins can grow.