A butter churn is a device used to convert cream into butter. This process is done through a crank used to turn a rotating device inside the churn. The agitation is the cream disrupts the milk fat. The membranes that surround the fats are broken down, forming clumps known as butter grains. These butter grains fuse with each other to form fat globules. Air bubbles are then introduced into the fat globules through the continuation of churning. As the butter grains become more dense because of the attachment of fat globules a liquid known as buttermilk is created. With constant churning fat globules form solid butter and the buttermilk is drained off. The butter is then squeezed of the excess liquid to form a solid mass.
A barrel churn worked by using a crank that would either turn a paddle on the inside or by actually turning the entire barrel. The barrel churn was one of the agricultural innovations of the eighteenth century.