To agitate cream briskly so that the fat separates from the liquid, thereby forming a solid (butter). The old-fashioned butter churn consisted of a container fitted with wooden blades that, when a crank was rotated, would whirl the cream inside until it turned to butter. The modern household substitute for a butter churn is the food processor.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.