How Do You Know if Butter Has Gone Bad?

Yes, butter, like all dairy products, can go bad. The most common way of telling is by distinguishing a characteristic "rancid" smell and taste, which will take over the usual flavor of butter.

For ages, butter has been considered a safe food to keep at room temperature for extended periods. Yet, in recent times, the question has begun to reappear — does butter go bad outside the fridge? While there are some things to keep in mind, it’s usually safe to store it on the counter. Here’s what you need to know.

Yes, butter, like all dairy products, can go bad — however, the complete answer is more complex than one might think. Butter is one of the few foods kept at room temperature for long times. Experts point out that most butter doesn’t go bad for at least three months.

The durability of butter, however, doesn’t result from the food itself. Instead, research suggests that butter going bad is almost exclusively the result of the processing it has gone through during its production. This includes two crucial aspects: pasteurization and salting.

Pasteurization is a heating process used to destroy pathogens in foods such as milk and butter. It’s one of the most important aspects of making dairy products and, if done incorrectly, can lead to spoiled foods. Poorly pasteurized dairy will allow living bacteria to remain in the finished product, which could keep multiplying.

Salting, on the other hand, is one of the most efficient ways of keeping bacteria out of foods. A high salt content reduces the amount of water in butter, preventing most pathogens from staying and growing in the product. While this doesn’t mean unsalted butter is unsafe, it is good to consider it the next time you’re doing groceries. 

While salted butter that has been correctly pasteurized may sound like it can’t go bad, it can also spoil due to oxidization. Oxidization is a chemical reaction that occurs in lipids when exposed to conditions such as sunlight and causes a rancid smell and taste.

Because butter is at least 80% milk fat, it’s very susceptible to oxidization. When kept in poor conditions, butter will not only become rancid but also lose some nutrients and become a perfect habitat for pathogens. 

For centuries, butter has been a perfectly good food to store at room temperature for extended periods. Only recently have some people started to keep it inside their fridges, mainly for fear that it’ll go bad, like other dairy foods when kept on the counter. However, studies show that keeping butter out of the fridge may be a good option.

As previously mentioned, the durability of butter doesn’t come from the food itself — instead, it has to do with pasteurization and salt contents. These factors have nothing to do with cold, and research suggests that you can keep salted butter in the open for at least three months. 

Yet, oxidization is an issue when considering butter kept out of the fridge. Heat can promote this process, causing it to go rancid and become a potential food-poisoning hazard. Similarly, some airborne pathogens present in the environment may find their way into the butter after oxidization has occurred.

For this reason, research points out that butter kept between 10° and 15° Celsius can last for more than six months. Instead, butter stored at room temperature is estimated to only last for three months. In any case, it’s unlikely that a stick of butter will be kept for over three months.

Many people keep butter out on the counter to keep it soft and spreadable instead of letting it become hard in the fridge. While there aren’t any specific instructions regarding how to keep it fresh on the counter:

• Store it in an airtight container
• Keep it away from sunlight
• Avoid leaving it outside the fridge on hot days
• Check it every once in a while for rancid taste and smell

Eating any food that’s spoiled can result in food poisoning, which is caused by bacteria and viruses. It’s hard to know precisely which pathogen will grow on spoiled butter, but there are a few general guidelines you can keep in mind if you suspect food poisoning. Eating spoiled butter often results in:

• Stomach aches
• Nausea and vomiting
• Diarrhea
• Fever
• Headaches

These symptoms can last for a few days — however, serious cases of food poisoning may drag over a couple of weeks. The severity of each case will depend on how spoiled the food was and which bacteria came in contact with the body.

Younger children, older adults, and pregnant women are at an exceptionally high risk of getting food poisoning. This is due to their debilitated immune system, so it might be a good idea for them to only buy salted butter and keep it in the fridge to avoid the most amount of bacteria. Similarly, people who have chronic diseases will also be at a higher risk.

If you suspect that you have eaten spoiled butter or are already food poisoned, it might be time to check with a doctor. Usually, they’ll recommend certain beverages for keeping your fluids at healthy levels and, sometimes, prescribe an antibiotic for the infection. In the most severe cases, you may have to be hospitalized.

It’s usually easy to tell if a stick of butter has gone bad, as it’ll display obvious visual and tasteable signs. The most common way of telling is by distinguishing a characteristic “rancid” smell and taste, which will take over the usual flavor of butter. If the butter hasn’t yet spoiled completely, you might notice a lack of taste instead.

Severely-spoiled butter will often look moldy, change color, and present yeast formations. This is relatively uncommon to find but is a clear sign that a particular food has spoiled well over tolerable limits. If you’re in doubt about whether your butter has spoiled, it might be a good idea to throw it away anyway — most of the time, it’s better to be safe than sorry.