Whether you’re making avocado toast or guacamole, avocados are a versatile, nutrient-dense food for any meal and any diet. However, once an avocado is separated from its tree, it can quickly spoil within days, according to Healthline.

So what are the signs when an avocado goes bad? And what are some ways to extend an avocado’s shelf life?

Why do avocados turn brown so quickly?

Avocados do not ripen when they remain connected to trees.

Darryl Holliday, an executive director of the Arkansas Food Innovation Center, explained to HuffPost, “You have to cut them down before they ripen, and there are so many seemingly minor things that can affect that process.”

Taste of Home shared that avocado — classified as fruit — has an enzyme called polyphenol oxidase. When it’s exposed to air, it causes the outer flesh to immediately start turning brown, while the inner parts stay green for longer unless the pit is removed. HuffPost added that this quick process is due to “the presence of phenolic compounds, which react with oxygen.”

In addition, like Holliday said, conditions such as skin cracks and unsuitable temperatures can increase an avocado’s browning process — which can harm its overall taste and appeal.

Here are some things to look out for.

Hard lumps

When an avocado looks to have small, protective lumps in the flesh, it simply means the avocado was damaged during growth, per HuffPost. They typically appear closer to the skin, but the lumps can develop closer to the pit and reveal the fruit as unripe.

The lumps are generally safe to eat, but since it may feel like a weird texture, it’s advised to simply eat around it.

Dark spots

According to Healthline, an avocado with multiple brown or black spots on its flesh essentially means the avocado is rotten. But if there is one isolated, brown-colored spot on the flesh, it won’t be harmful — but it’s recommended to cut that spot out for safe measure.

“The brown spots aren’t as flavorful, so you may want to cut them away,” Janilyn Hutchings, a food scientist for StateFoodSafety, said to HuffPost.

Stringy flesh

Ever tasted a tough, fibrous avocado? Holliday explained to HuffPost that storage temperature is the reason for this.

Because of its vast vascular tissue system, when temperatures are too hot during ripening or too cold, too quickly, cellulose strands from the outer flesh don’t fully ripen, therefore leading it to hold a stringier consistency.

Healthline stated its fibrous texture may associate more with growing conditions than a sign of expiration. As long as an avocado doesn’t appear to have other signs of spoilage, it could be OK, given its taste and texture are OK.

Despite this, an avocado with darker streaks may warrant caution.

Black skin

The majority of avocados eaten are the Haas variety — and they develop skin color changes over time.

A Haas avocado appears bright green and bumpy when not completely ripe, eventually turning darker during and after the ripening process. When it looks to be black, or near to, it’s a sign it’s overripe, especially if its texture feels mushy, per Healthline.

What to know when buying avocados

HuffPost recommended looking for avocados without observable bruises and blemishes. In terms of color, find a lighter green-skinned one for ripening or a darker one that “yields under slight pressure.”

If you want to keep it around longer, Taste of Home provided some options to prevent an avocado from browning, including:

  • Submerging it in refrigerated water.
  • Pressing and sealing it with plastic wrap.
  • Brushing vegetable oil or olive oil around it.
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