Whether it's OK to leave butter out at room temperature or not is a hotly debated issue. I grew up thinking never to do this — that it would most definitely go bad. With that mindset, I've always stored it in my fridge and taken out just a serving or two to soften if we are having something like toast that requires it to be spreadable.
But the truth is that it's perfectly fine to keep butter at room temperature. Yes, it is a dairy product, and dairy products degrade when left out at room temperature, but butter is at least 80 percent fat and has a much lower water content than other dairy, which makes for a product that's much less susceptible to bacterial growth.
The bigger concern for room-temperature butter is that it will go rancid. But that won't happen as quickly as you might think — especially if avoid these four mistakes.
1. Leaving the wrong type of butter out.
It's fine to leave unsalted butter out on the counter for a few hours if you're planning to bake with it, but if you're going to leave any butter out at room temperature for an extended period of time, make it salted. That's because the salt in salted butter adds extra protection against any sort of bacterial growth.
2. Storing it in the wrong container.
Exposure to light and air are the two main reasons butter goes rancid or spoils, which means it's wise to be savvy about the container you're storing the butter in at room temperature. Leaving it out in simply the wax paper wrapper it came in or even just on a plate wrapped in plastic wrap should be avoided. Instead, choose a butter dish that keeps the light and air out.
You can also opt for a butter crock, also called a butter bell or butter keeper. With these containers the butter is kept in a small pot that is immersed in water, creating an airtight seal. Both a dish and crock also help keep the butter soft and spreadable while at a steady temperature.
3. Leaving it in a very warm kitchen.
If you live in a warm climate or it's the peak of summer, your kitchen just might simply be too warm to leave butter out on the counter. If the temperature in your kitchen hovers steadily above 70°F, you're better off storing butter in the fridge.
4. Keeping too much out at once.
The USDA recommends leaving butter out at room temperature for only a day or two. But if it's stored in all of the proper conditions listed above, it can stay fresh for up to two weeks. So don't leave out more than you think you'll be able to get through in that small period of time.
If you're unsure if your butter is OK to eat, simply give it a smell. If it's rancid it will most definitely smell off, and if you're willing to give it a taste, it should taste unpleasantly sour. At that point it's time to reach for fresh butter.