Myth: Butter Spoils if Not Refrigerated
False. Butter does spoil, but much more slowly than fresh (unfermented) milk products, such as, well, milk. The reason? “Most butter contains added salt, which impedes the growth of spoilage bacteria,” says John Bruhn, a dairy-foods processing specialist at the University of California at Davis. Today’s salted butter, in normal usage, will rarely spoil, even if you leave it unrefrigerated all the time. Unsalted butter might spoil in about a week, but it contains enough natural salt to slow the growth of bacteria that cause spoiling. So you don’t have to worry if you forget to put the butter away after dinner.