I grew up in a family that was scrupulous about food safety, and it took me a little while after I moved out to figure out the difference between what was a sensible precaution (wash your hands after touching raw meat) and what was not (you must throw out yogurt that is a day past the sell-by date). The first time I heard that some people keep butter on the countertop, I was scandalized. That sounded deadly.
But it’s not uncommon for people to leave their butter out 24/7 and live to tell the tale. Ask around, and you’ll find plenty of people—especially older folks—who keep a stick of butter out of the fridge all day, or all week. Some simply have a butter dish that lives on the counter instead of in the fridge.
The danger of bacterial growth is minimal
The main reason we keep foods in the refrigerator is to slow bacterial growth, and the growth of other microbes like fungi. But bacteria can’t thrive in a stick of butter. There just isn’t enough water available for them to grow, since butter is mostly fat. What little water is in a stick of butter exists as droplets scattered throughout the stick—and if the butter is salted, that water is salty and even more inhospitable to microbes.
We’ve even included butter in our list of foods that you don’t need to refrigerate, alongside honey, oils, and hot sauce.
Butter keeps better in the fridge, though
If, inspired by this information, you choose to simply keep your butter out on the countertop, you may notice something: where the butter touches the air, it gets to be a darker color, and over time the flavor and smell may change a little. That’s from the fats oxidizing. Another phrase for this is “going rancid.”
Now, rancid isn’t the same thing as going bad. A lot of our foods change in flavor over time as their fats oxidize. That’s why old nuts taste funny, and why that bag of whole-wheat flour that’s been in your pantry forever might not make as tasty a loaf of bread as if you went out and bought a fresh bag. Foods that are rancid aren’t unsafe, but if you’re picky, they may be unappetizing.
If you want your butter to keep its fresh flavor longer, it makes sense to keep it in the fridge. The USDA confirms that butter kept at room temperature is safe, but that you probably want to use it up “within a day or two” to avoid rancid flavors.
How to get the best of both worlds
If you like soft, spreadable butter but you want to keep it tasting fresh as long as possible, you have a few options.
One is what the USDA hinted at: you can figure out how much butter you’re likely to use in about two days, and leave that much in a butter dish on the counter. The rest stays in the fridge while it waits its turn.
Another is to use a room-temperature container that is designed to keep butter away from the air, so it lasts longer. This is the idea behind old fashioned butter bells. The bell holds a glob of butter upside-down in a bowl attached to the lid, and then you fill the base with water to make an airtight seal. If that sounds like too much trouble, you can use any covered dish and still get most of the benefits. Just make sure to finish it off before too long.