How Long That Jar Of Mayo Will Really Last After Opening

Mayonnaise aficionados have divided themselved into some of the fiercest factions on earth. There are those who swear by Duke's (particularly folks in the South), those who would raise hell for Hellman's, and those who quietly but devoutly prefer Blue Plate, the best mayo you likely don't know about. It's also not uncommon for mayo fans to open a fresh jar, only to find an old one in the back of their fridge. Sure, it looks okay, but how long is mayo actually good for after opening?

Store-bought mayo that has been opened and consistently refrigerated is good for about 2-3 months. (On the other hand, homemade mayo will only stay good for about a week.) Before mayonnaise is opened, it's considered shelf-stable thanks to its acidic ingredients (like vinegar) and salt content. Once it's been opened and exposed to both the air and utensils, however, it's considered contaminated and must be refrigerated from then on to slow the inevitable growth of bacteria (and preserve the flavor and texture).

Also, an open jar of mayonnaise should never be left out for more than two hours. At the two-hour mark, its temperature will rise into bacterial growth territory. Unfortunately, if you've left a jar out for longer than that, you should probably throw it away and buy a new one.

If you reach for an open jar of mayonnaise from the bowels of your fridge but can't quite make out the Best By date, here are some tips for discerning whether or not this condiment is still good. First, a sniff test. If there's anything sour or foul about the way your mayo smells, it has likely gone bad. A rank odor upon first opening the jar is a clear sign of spoilage.

The next signs are visual. Even if the smell is still faint, if the mayo has changed from a creamy off-white to more of a yellow (or even a brown), it's past its prime and should be tossed. The same goes for visual signs of mold growth. Even though many people are comfortable cutting a moldy section off a piece of hard cheese and still using the rest, mayonnaise is soft, meaning the mold's "roots" could be more widespread throughout the entire jar. It all has to go.

Finally, if the mayo has changed in texture — if there's separation, if the creaminess has been replaced with clumpiness, or if there's a thin film or liquid on top — it should go out of the fridge and into the garbage.

Store-bought mayonnaise that hasn't been opened can sit in your pantry for a long while, and it may even be consumable past its Best By date. In fact, this date is simply the manufacturer telling the consumer when the product's quality might start degrading (while still being fully edible).

If you discover a jar of mayonnaise that's past its Best By date, consider a few things before using it. Has it been kept out of direct sunlight in a cool, dry location like your pantry or some other kitchen cabinet? Is the jar intact, including the inner seal? Once opened, do you smell or see any of the spoilage signs listed above, like discoloration, mold, or separation? If you're satisfied that the mayonnaise is still good, you can go ahead and eat it, and it should keep in the fridge for another 3-4 weeks.