How Long Does Mayo Last Unrefrigerated?  (When Does It Go Bad?)

Everyone knows the tell-tale signs that summer is finally taking off. Between the barbecues, picnics, beach trips, and camping plans, each year the warmer weather brings fun outdoor activities filled with great food. 

And with the great food always come certain warnings: drink plenty of water, keep your ice in a high-quality cooler, and don’t leave your mayonnaise out in the sun. 

That last instruction (which usually comes from an overly-concerned mother) always tends to cause a bit of controversy.

So the question remains: how long does mayo last unrefrigerated?

It’s always a good idea to know what the mayo shelf life is, but how long is it safe to keep it out of the fridge – whether it’s in your potato salad or sitting in the cooler? 

The Myth

People often assume that mayonnaise is the source of potential food-borne illnesses.

The belief is that when you let mayo sit outside, unrefrigerated and unprotected, it becomes more and more susceptible to bacteria.

Some Background

The myth of mayo stems from the fact that mayonnaise contains egg. The FDA offers strong recommendations for food safety when it comes to eggs and foods containing eggs.

Since this chicken by-product can contain Salmonella, they advise individuals to not only keep eggs refrigerated, but to ensure that they are fully cooked before eating. 

Salmonella is a group of bacteria that is common in causing food poisoning, which can result in fever, abdominal pain, diarrhea, and vomiting. In some rare extreme cases, it can even cause death. 

Likewise, the FDA also provides strict serving guides when it comes to eggs and egg dishes. These experts say it is best to serve any foods made with eggs immediately after serving.

If you intend to serve them later on, then they need to be refrigerated until then.

Furthermore, any egg dish that needs to be served warm should be reheated to a temperature of 165 degrees before serving. 

To take things a step further, the FDA states that cooked eggs should never be left out of the refrigerator for more than two hours – and just one hour in very hot temperatures.

The reason behind this is that bacteria will grow more quickly in warm temperatures, increasing the risk of food poisoning. 

When we take all of that information into consideration, it makes sense why people would jump to the conclusion that mayonnaise, which contains eggs, would fall under this same category and rules.  

The Truth

The truth of the matter is that your potato salad containing mayonnaise will be just fine to leave out at your next family picnic, and there’s a very, very slim chance that it will harm anyone at all.

Although the product does use eggs, it does not follow the same rules as eggs on their own do. 

Generic, typical, store-bought mayo is usually made with some kind of acid – most commonly, vinegar or lemon juice.

Because the product is acidified, it actually kills any food-borne pathogens it comes into contact with. 

So not only will there not be any Salmonella in your mayo, but your mayo will prevent any other bacteria from forming.

In a way, the mayonnaise is actually protecting you and your family. The same is true for other dressings as well.  

If someone gets sick from eating potato salad outdoors, it’s more likely that the potatoes caused it and not the mayo.

So How Long Does Mayo Last Unrefrigerated?

You’ve probably noticed that mayo is not kept in the refrigerator section of the grocery store.

Because it has been pasteurized, it has a decently long shelf life while the container is still sealed.

You’re safe to keep it unopened and sealed in your pantry for about three or four months after its “best used by” date.

If for some reason you’re looking to store mayo for longer, you can refrigerate it unopened and sealed for up to a year.

Even though mayonnaise contains acids that will help kill off bacteria, it still should be refrigerated after opening.

So long as you do this, it’ll keep for a good two or three months.

However, unrefrigerated, your open jar of mayonnaise will probably be bad after about eight hours.

If you’ve accidentally left it out on the counter overnight, the safety option is to toss it. 

Some easy signs to tell if your mayo has gone bad is signs of mold or spore growth, or a horrible smell. Your mayonnaise may also be a couple shades darker than usual, too. 

Conclusion

There may be foods at the barbecue that can potentially house harmful bacteria, but your mayonnaise is not to be blamed for any food-borne illnesses.

With the amount of acid added to this product, not only is it safe to keep outside, but it has a long shelf life, too. 

You can certainly leave products with mayo outside at an event for a few hours, but it’s also a good idea to keep a cooler handy for particularly long, hot days.

Your potato salad will taste better cool, anyway!