You can tell a lot about a person by where they store their butter. In the refrigerator? They’re probably overly cautious about safe food practices and they don’t mind struggling with an uncooperative stick that needs to be mashed into toast. On the counter? They’re too busy to bother with spreading issues. They want something the consistency of yogurt.
But are the room temperature butter people taking any kind of risk? Does butter really need to be refrigerated?
The answer is: It's probably a good idea to keep your butter in the fridge, but there are some things you should know.
Butter is the butterfat left over when milk or cream is churned and the solids separate from the buttermilk. While dairy products are usually prone to spoilage, pasteurized butter has enough fat and salt to inhibit bacterial growth. According to the U.S. Department of Agriculture, butter can safely be left out for two days. Leave it sitting there any longer and it could turn rancid, affecting flavor.
Keep in mind that multiplying bacteria is just one way table butter can become contaminated. If people are dipping a dirty knife into the stick, those germs can make their way into your butter dish.
Salted butter is the safest type to leave on the table, as the salt acts as a kind of preservative and may stave off spoiling. With unsalted butter, you might be tempting fate a little more.
As for margarine: Because it contains more water than regular butter, the potential for bacterial growth is greater. While it technically can be left out for a day or so, you’re better off keeping it cold.
If you’re using unpasteurized or homemade butter, all bets are off—refrigeration is a must.
A general rule of thumb is that you’re probably OK leaving salted butter out for a day or two provided the room stays around 70° F. If it’s warmer, or anyone in the household has issues that might make them more prone to foodborne illness, keep it in the fridge. And always use a clean knife.
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