Butter Safety

• Butter in the U.S. is made from pasteurized milk, which significantly lessens its chances of contamination with bacteria that cause foodborne illness. While butter can technically grow mold under the right conditions, it is not likely. With a water content of less than 20 percent, the ability to grow any pathogen when left unrefrigerated is unlikely. But the recommendation for prolonged shelf life and quality is to refrigerate butter until you are ready to use it.

Salted vs. Unsalted

• Salted butter will rarely spoil even when left unrefrigerated indefinitely, claims John Bruhn, a University of California at Davis dairy-foods processing specialist. Unsalted butter is another story. While unsalted butter will spoil in about a week, unsalted butter has enough natural salt present to stave off spoilage for about a week when it is left unrefrigerated. Salt, a natural preservative slows the growth of harmful bacteria in foods, including butter.

Storage Basics

• While butter won't spoil quickly, quality is another issue. Butter easily picks up odors of other foods and proper storage is important to retain its original flavor and so it doesn't become rancid. Butter should be refrigerated in its original wrapping. Removing its wrapping exposes it to oxygen which can lead to faster deterioration of taste and allow it to pick up off-odors that affect its flavor. Store butter in the coolest area in your refrigerator for up to two and a half weeks. For longer storage, freeze butter for up to four months.

Room Temperature Butter

• Many recipes call for room temperature or softened butter. In this case, remove the butter from the refrigerator around 15 minutes before use to allow it soften. Using a microwave to quickly soften butter is also useful, although it is important that you do not liquify it by overheating it. In most microwaves you are able to soften a stick of butter in about 10 seconds. For larger quantities of butter, increase this time slightly, but keep a close eye on the butter so you don't melt it.