Why You Should Store Cut Avocados With Sliced Onions

There is no greater pleasure than cutting into an avocado and finding its soft, green flesh perfectly ripe. Their timing is notoriously finicky ... one minute they're hard as rocks, then the next thing you know, they're overripe and past their prime. Or worse, you slice one open and use half, and then by the time you go to use the other piece, it's turned brown and mushy.

We know how to slow down avocado ripening by storing them in the refrigerator, but keeping them from turning brown once they've been cut open isn't as simple. While there are numerous storage methods found online that claim to keep cut avocados from browning, they can be hit or miss, and some are even dangerous. There is one hack, however, that actually does work and has the science to back it up — the trick is to store cut avocados with sliced onions.

When you cut into an avocado, exposure to air is what causes it to brown. On the other hand, when you chop an onion, it releases sulfites. Like a match made in heaven, sulfites slow down the oxidation process in avocados, preventing their discoloration from happening so quickly. For this to work, use an airtight container like lidded Tupperware, and line the inside with pieces of onion. Place your cut avocado on top, seal the container tightly, and store it in the fridge. This technique will buy you at least a few more days of gorgeous, green freshness.

The chemistry behind why onions prevent brown avocados

The fun science part helps to explain why avocados turn brown in the first place, as well as why onions hinder them from oxidizing too quickly. Browning is caused by an enzyme called polyphenol oxidase, which — along with avocados — is also in apples, peaches, pears, bananas, potatoes, and mushrooms. When exposed to oxygen, the enzymes catalyze into melanin — this is the same brown pigment that colors our hair, eyes, and skin tone. The sulfites released by onions function as a natural anti-browning agent by inhibiting avocado enzymes from reacting with the air. 

Of course, we'd be remiss not to acknowledge the obvious, and that's the pungent smell and flavor of onions. When storing chopped onions, their strong scent permeates; every time you open the refrigerator door, you get a whiff of onions. Needless to say, storing them together will transfer both their odor and their flavor to delicate-fleshed avocados. 

This isn't necessarily a bad thing, as long as you don't use oniony avocados in sweet applications where the aromatic essence would ruin the taste. Instead, stick with savory uses for the fruit where the pairing goes well together. Your best basic guacamole recipe is an excellent choice because it's already made with both ingredients. You might as well give those onions a second life as well ... go ahead and use them in your guac, too. Onion-infused avocado will also do well on toast, in pesto, or folded into omelets.

How to safely store cut avocados for freshness

Other storage suggestions touted online include leaving avocados with their pit, coating avocado halves with oil, enclosing them in plastic wrap, or all three at once. These all operate on the premise of keeping air from interacting with the exposed flesh. Another popular hack is to douse cut avocado in lemon or lime juice. Citric acid lowers avocado's pH, which in turn inhibits the enzymes from setting the browning process in motion. Although this method can work, the juice can affect the fruit's texture, turning it gummy or slimy. 

A word of caution: One storage method that went viral on TikTok has been found to be unsafe. The idea is simple enough; just store avocados (cut or whole) submerged in water. This is said to keep them fresh and green for weeks at a time. The problem with this, according to the FDA, is that avocado peels can harbor microorganisms that cause food poisoning, like Salmonella and Listeria. In fact, in a statement to Good Morning America, the FDA specifically warned against soaking avocados, stating that these pathogens "that may be residing on the avocado surface may potentially multiply during the storage when submerged in water."

There's no reason to mess around with food-borne illnesses just for the sake of tasty avocados. The next time you need to keep some from going brown, store them with onion slices for an easy and effective way to maximize freshness.