How to not poison yourself and your loved ones.
How did people chill their butter before the age of refrigeration? For the most part, they didn’t. In temperate climates, you can leave butter out at room temperature for a week or even longer before it starts to turn, and even then, the butter won’t actually spoil; it will just go rancid, which is less scary than it sounds.
Rancidification occurs when fats oxidize and hydrolyze into other compounds, and is completely different from curdling or rotting. It’s a natural part of the aging process for some cheeses and cured meats, and in butter, it manifests as a dark yellow color and twangy flavor that, over time, can taste downright nasty. All butter goes rancid, even sticks securely in a fridge, and a quick sniff check is all you need to tell if your butter has gotten too funky for your tastes.
For best results, pack your room-temp butter in a French crock to keep it from absorbing kitchen odors, and eat it within a week. After all, that’s why you’re leaving it out in the first place.