This trick for keeping my half avocado from going brown blew my mind

Avocados are notoriously one of the most fickle foods in the produce section—scratch that, in the entire grocery store. After waiting patiently (so patiently) for it to ripen, once you slice that baby open, you have just a few hours to use it before brown spots start popping up, threatening to turn the entire thing the color of poo.

Watch the video below to find out if avocados are really as healthy as they’re hyped up to be:

The thing is, using a whole avocado on your morning toast or in your smoothie is…a lot. Half or even just a fourth is typically filling enough. (Unless you’re making guac.) But it still sucks to have to put away that half of your avocado and know that it’s probably going to be brown and spotty and sad the next time you want to eat it. (Unless you stick it in the freezer…)

Fortunately, registered dietitian Toby Amidor, RD, has a handy little hack for how to keep sliced avocados from turning brown. “One way to prevent an avocado from browning is to pair it with an onion,” she says. Seems simple, right?

Why? Well, when avocado flesh is exposed to oxygen in the air, a chain reaction called oxidation occurs. This reaction deteriorates the quality of the avocado and makes it ripen and age faster, causing brown spots. (This happens with a lot of other foods, including apples and bananas.) However, onions contain sulfur, “which slow the oxidation that causes browning,” says Amidor. Think of the sulfur as a protective shield that helps your avos stay green and gorgeous for longer.

“[To try this], chop an onion and place a cut-open avocado, flesh-side up, on the onion in an airtight container or bag,” Amidor says. Then, store it in the fridge. The onion should give your avocado a couple extra days of life.

Of course, if you have no onions to spare, there are other ways to keep your cut avocados from turning brown. “Once you open up an avocado, throw it in the refrigerator [and] secure it with plastic wrap,” Tracy Lockwood Beckerman, RD, previously told Well+Good in an episode of You Versus Food. That way, you’re protecting it as much as possible from the oxygen exposure that leads to browning.

However, there is an added bonus of the onion method: you can use it to top off your avocado toast, too. Win-win!