How does the milk turn to butter after churning it?

When whole milk sits out, tiny fat molecules float to the top, forming a layer of cream that can be skimmed and collected.

To make butter, the cream is agitated (stirred up) so that the fat molecules get shaken out of position and clump together. This is known as Churning.

Churning is the process of shaking up cream or whole milk to make butter, usually using a butter churn.

During the churning process, the cream is violently agitated to break down the fat globules, causing the fat to coagulate into butter grains, while the fat content of the remaining liquid, the buttermilk, decreases. Thus the cream is split into two fractions: butter grains and buttermilk.