Milk curdles and cheese gets moldy, but what about butter? Many people leave a stick of butter on the counter without thinking twice about it. Others religiously keep their butter in the fridge after each use.
So who’s right? Does butter go bad if you leave it out?
Butter is not a TCS food
Dairy is one of the major food groups categorized as a Time/temperature Control for Safety (TCS) food. TCS foods can be dangerous to eat if not kept at the correct temperature for the correct amount of time. Dairy products should be stored at 41 degrees Fahrenheit (5°C) or lower to avoid bacterial growth. If a dairy product is in a temperature higher than 41 degrees for 4 hours or more, it must be thrown out.
Butter, however, seems to be the exception to that rule. According to a report by the FDA, pasteurized butter is not a TCS food, meaning it does not have to be refrigerated to keep it safe.
But if butter is made from cream, a dairy product, why can it be left out? One word: pasteurization.
Pasteurization lowers bacteria counts in the cream to safe levels, and then once the butter is made, its physical properties protect it from bacterial growth. Bacteria need water to grow. Butter consists mostly of fat (at least 80%) and water. The water content is fairly high, but due to the churning process, water molecules are separated and surrounded by fat, which is almost impenetrable to bacteria. Even if bacteria do get to the water, they don’t spread easily to other pockets of water due to the fat. Also, bacteria are even less likely to grow on salted butter.
Other factors in butter storage
So are those people who refrigerate their butter just paranoid? Well, there are other factors to consider in butter storage:
- When butter is left out, it can easily become contaminated with elements in the environment such as dust and TCS foods. When butter becomes contaminated with TCS foods, it also becomes a TCS food.
- After a certain amount of time, the water molecules will interact with the fat in the butter, which leads to the decomposition of fats, a process accelerated by light that causes butter to become rancid and lose its fresh taste. This process of decomposition can be slowed by covering or refrigerating butter.
- Unpasteurized or any homemade butter is considered a TCS food. Only pasteurized, commercial butter can be left out.
- As an extra precaution, it is recommended for commercial kitchens to keep all butter refrigerated.
How long can butter sit out?
Butter, like all food products, will spoil eventually. There is still a debate as to how long butter can sit on the counter before going bad. For best quality, keep butter in a covered dish and use it within 10 days. You can also refrigerate or freeze butter to extend its shelf life.
To sum up, you don’t need to panic if your cookie recipe calls for butter at room temperature. And if you like to keep the butter out to keep it soft and spreadable, you’ll be fine as long as you keep it covered and use it within a few days. But if you prefer to keep your butter rock-solid and fresh in the fridge, that’s okay too.
Learn more about TCS foods and other food safety tips in our food handlers training.
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— Sophie Buckner
Editor’s note: This post was originally published in June 2015 and has been updated for freshness, accuracy, and comprehensiveness.