My ex-wife’s uncle always left his butter out on the kitchen table. I never understood that! (He also left his mayonnaise out on the table, too, but…well, one issue at a time.) The butter on the table always bothered me because…well, room temperature butter would be kind of risky, health-wise, right? I mean, shouldn’t butter be refrigerated? Well, the real answer is yes, you should keep your butter in the fridge. But it isn’t as much of a hard-and-fast rule as you or I might think.
What is butter? Well, it’s actually leftover butterfat from churned milk or cream, where the solids separate from the buttermilk. Most dairy products are prone to spoilage, but pasteurized butter actually has enough fat & salt in it to inhibit bacterial growth. The U.S. Department of Agriculture actually says butter CAN safely be left out…but only for up to two days. Any longer & it’s likely to go rancid. And that’s just one way butter gets contaminated: there are also some folks who regularly use dirty utensils to serve their butter, which can transfer germs into it.
Salted butter is the safest to leave on the table, since salt acts as a preservative & can likely keep things from spoiling (for a while, at least). You’d certainly be tempting fate a bit more by leaving unsalted butter out. And if you use unpasteurized/homemade butter, then there’s no question: you must refrigerate.
What about margarine? Well, margarine actually contains more water than regular butter, so there’s an even higher potential for bacterial growth. So, while it can technically be left out for a day or so, you’re better off keeping your margarine cold.
The general rule of thumb is that it’s probably okay to leave salted butter out for just a couple of days, and only so long as the room it’s in stays around 70° F. Any warmer than that, then you’ll need to keep it in the fridge. Hey, if you’ve got a refrigerator then why not use it?