A friend of mine asked me the other day about butter- “to leave it out or not to leave it out?” In my childhood household, both were common, and we routinely had a dish of butter on the counter for morning toast. When I asked my mum her thoughts, she pointed out that her childhood home had always left the butter out in a dish- but that they hadn’t had a refrigerator, and hadn’t lived in a hot climate. (Ah, Dublin in the 60’s.)
A little digging turned up some interesting points-
The case for leaving butter out: As butter is mostly fat, with a low water content, and often a large amount of added salt, it is unlikely to spoil rapidly if left out. The rule of thumb is that butter in a butter dish will last roughly ten days before rancidity may occur (though temperature, the type of dish, and whether the butter was made with pasteurized milk, can effect this average.) If you have a large family and use butter regularly, making it to ten days seems unlikely. For those with European leanings, there are butter crocks designed to increase the butter’s out-of-fridge life by as much as two weeks. It is important to note that butter softens at roughly 60 °, so this is the mean “room temperature” often referred to. If your internal room temperature exceeds 70°, it is time to refrigerate.
The case for refrigeration: If you live in a region where your average room temperature is 70° or higher, then refrigeration is a good idea. If you are a pastry chef, chilled butter is also preferable. Finally, if you use butter very rarely, keeping it in the fridge and softening it (roughly 30-45 mins at room temperature) is likely the way to go.
In either case, you needn’t fear- rancid butter is not harmful, just unpleasant. To avoid this worst case scenario, use the sniff test- if it smells “off,” dispose of it. Keep in mind that butter is susceptible to absorbing the aromas of it’s surrounding food, so if you keep it on the counter, make sure it is separate from any aromas you may not find appetizing.
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