Shaking a mixture until it gives up
How Does Cream Turn Into Butter?
Cream is fat droplets floating in water. Churning breaks their coats so they join up.
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Step 1 of 5
Cream is fat hidden inside water.
Cream is not fatty water. It is fat parcelled up and kept in suspension. Milk fat travels as microscopic droplets, each wrapped in a membrane that keeps it apart from its neighbours and spread through the water.
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Step 2 of 5
Whipping first traps air.
A halfway stage — still a mixture, not yet butter Beating folds air bubbles in, and partly damaged droplets stick around them. That scaffolding is whipped cream — a halfway stage.
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Step 3 of 5
Keep going and the coats break.
More beating smashes the membranes open. Bare fat is sticky, so exposed droplets grab each other instead of the water.
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Step 4 of 5
The mixture suddenly splits.
Within a few seconds the fat gathers into grains and the watery part — buttermilk — is left behind. Cooks call it the break.
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Step 5 of 5
Working and salting finish it.
Squeezing the grains presses out the last buttermilk, which would otherwise spoil, and salt draws out more and keeps it longer.
Butter is roughly 80 per cent fat and 15 per cent water, which is why it spits when it hits a hot pan.
The short version
Churning breaks the coats off cream's fat droplets so they clump into butter and leave the watery buttermilk behind.
Try it yourself
Half fill a jar with double cream and shake it. Whipped in two minutes, split into butter in about ten.