Food Safety

How to Tell if an Avocado Is Bad

Dark green doesn’t necessarily mean rotten.

July  6, 2020
Photo by Ty Mecham

A few years ago, an Australian company called Naturo Technologies invented a machine—the Natavo Zero, aka the Avocado Time Machine. This ATM supposedly miraculously slows the avocado ripening process, keeping it from turning brown for up to 10 days without the use of chemicals—or olive oil, or lemon juice, or red onion. (Naturo Technologies is currently working on a new process of pasteurization that leaves more of the natural vitamins and enzymes in the milk.)

The implications of this Avocado Time Machine? Let’s say you did all the sleuthing at the store for the perfectly-ripe avocado: You sought out fruits (yes, they’re a fruit) with a darker green, almost black skin color. You squeezed only a handful (ha) of avocados at the store (applying gentle pressure only, obviously). You found the one that was perfectly ripe and ready, and nicked off the stem to check the color of the round (perfectly light green). But then, you got home, and forgot about the avocado—not remembering until days later, and your once-perfectly ripe avocado is now a brown and mushy avocado.

When the ATM was first getting publicity, it seemed like everyone I knew emailed me one article or another (from Mashable, Eater, Foodbeast, Food & Wine, Grub Street, Tasting Table...). Even my dad told me about it!

But here's the thing: Rather than being marketed or intended for home use, the machine is meant for large-scale food service. A press release from the company states that the "list of possible beneficiaries is long and includes the food service, quick service restaurants, catering companies, canteens, sushi chains, supermarkets and all kinds of retailers. It also permits the export of locally grown avocado fruit to countries with difficult import restrictions or hard to access markets." Moreover, the ATM, says Naturo, eliminates potential pathogens at a level that exceeds the strictest food safety codes—its benefit is in increased food safety, not just in aesthetics.

As Clint Rainey of Grub Street put it, "The idea is cool and all, even if it’s the work of somebody whose plan seems to be tackling the world’s problems in reverse order of importance, and is of absolutely no benefit to home cooks." So why all the attention? What's with our never-ending obsession with keeping avocados as green as possible as long as possible? What's really going on when an avocado turns brown? Is it just an unsightly, unappetizing phenomenon—or can you really taste the difference?

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Top Comment:
“I think I understand it even less now that I read this article. This is how I perceive the life of an avocado. Not ripe, not ripe, not ripe, not ripe, not ripe, not ripe,ripe, rotten. ”
— Frank
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The FAQ page of Avocado Central, a website run by the Hass Avocado Board, does not offer much information beyond, "Oxidation (exposure to air) can cause the fruit of an avocado and/or guacamole to turn brown." Kids' stuff.

Compound Interest, a site (and accompanying book) that dives into the chemistry of everyday food and drinks, offers a bit more explanation: In the presence of oxygen, the enzyme polyphenol oxidase converts the phenolic compounds in the avocado into quinones (more on how quinones affect flavor later). These quinones polymerize—they join smaller molecules into long chains—to create polyphenols, and it is this polymerization that appears as the brown coloration. It's not only oxygen exposure that results in the browning—it's also the damaging of the structure of the plant cells, which allows the phenolic compounds and the polyphenol oxidase enzyme to interact.

The ATM works to combat this by using steam to create pressure fluctuations that "switch off" polyphenol oxidase, thereby slowing the browning process.

If all that went over your head and you just want to know whether avocados that have browned from oxidation actually taste worse, here’s Monte Nesbitt, an Extension Program Specialist at the Texas A&M AgriLife Extension, to explain.


How to Tell if An Avocado Is Bad

1. Check the Color.

Not oxidation (your light green avocado turning dark green, even brown), but quinones "are responsible for bitter flavor,” Nesbitt says.”There can be some loss of eating quality as the process continues, although perceptions of these bitter flavors vary among people.”

Dark green flesh doesn’t always mean avocado is rotten.

So the impact of oxidation on avocado flavor is a bit up in the air. Eric Focht, a staff research associate at the University of California Riverside, said he wasn't aware of any blind taste tests of browned versus freshly-cut fruit. But, he'd "bet that if the subject couldn't see what they were eating, they'd notice little difference; I know I don't." Most of the aversion, he hypothesizes, is psychological: "We don't like the way it looks, so it's off-putting. A big part of food is its presentation, and we associate browning or discolored fruit with being bad or overripe or even rotten."

Our blind taste test. I don't want to eat that avocado on the right, even though I know it doesn't taste *that* different. Photo by Mark Weinberg
Dark green or gray flesh can mean chilling injury.

"On the other hand," Focht reminded me, "there are types of browning and discoloration in avocado fruit that DO affect flavor"—like chilling injury, which is browning or blackening of the skin and browning or graying of internal flesh due to low-temperature storage—"and it's important to distinguish between [these] and phenolic response."

So, a few years ago, we did a mini, totally unscientific, mostly anecdotal blind taste test at the Food52 offices. One of our avocados was truly funky—brown-gray from the moment we opened it up—and it tasted discernibly different, though not bad, per se: more like there was something obscuring the true avocado flavor; then-staffer Amanda Sims put it well when she said it tasted like an unripe avocado (slightly blah-ish) but with a soft texture.

The avocado that was pristine when we cut into it but left out to brown for a few hours, on the other hand, was harder to differentiate from the freshly-cut one: Maybe it tasted slightly bitter... maybe. It was hard to say! (Of course, the oxidation that occurs after a few hours is surely less impactful than oxidation that happens over a number of days.)

In all scenarios we realized that avocados—at least the ones we're getting in New York City (that is, shipped in from Mexico and California)—aren't so palatable on their own. But when you add the necessary salt and pepper and lime juice, any deterioration in taste due to oxidizing probably wouldn't be noticeable at all.

2. Taste it. (Yes, really!)

As for safety concerns? Nesbitt said that there's "no safety problem with consuming dark avocados unless they have also been exposed to room temperature and bacteria, thus recommendations to refrigerate them are valid." So if you're tasting something funky or rancid or "off" in your brown avocado (or the sandwich you're saving for the next day), it's important to think about why it's brown: It could be due to something other (or maybe more nefarious) than oxidation.

If presented with an unsightly, but otherwise very fine (largely light-green-fleshed, some dark bruisings OK, buttery but not liquified, absolutely no foul smells); avocado, we’re on Team Just Eat It. And it sounds like you are too: When we asked you your feelings about oxidizing avocados, most of you commented that you simply cut around discolored areas or use the less-than-perfect fruit in smoothies, on toasts, or in guacamole.

But! If you can't get behind browning avocados (and you're upset that the Natavo Zero is meant for commercial use, not home kitchens) and they do taste bitter or funky to you, you can take precautionary measures to stymie their browning (counterintuitively, the best choice may be to do nothing at all!).

Or, you can seek out special varieties less prone to browning (many of which aren't available in all parts of the country). Focht told me that "some avocados suffer from [browning] a lot more than others and Hass is one of the varieties that does have particular problems with browning after the flesh is cut. Many other avocados, however, show a significantly less pronounced response" and "some of them really do not seem to brown at all (Sir Prize, a UCR release [a cross that originated at UC Riverside] from the late 90s comes to mind)."

How do you tell if an avocado is good? Share your tips with us in the comments!

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I used to work at Food52. I'm probably the person who picked all of the cookie dough out of the cookie dough ice cream.

33 Comments

AGracie324 August 4, 2020
Living in AZ, we have the good fortune of getting avocados from the local Hispanic groceries that are just perfectly ripe..wonderful. My general notion is to eat the whole thing.....no problema! The other notion is ....if it looks gross, don't eat it! Works for me!
 
judy August 4, 2020
I grew up inSo. California, and have been eating avocados all my life--now 65. Though it is not rocket science, it does take some general experience to buy and keep avocados and be able to use them when desired. I am a great fan of Debbie's green bags and containers. They do prolong the life of fruits and veggies. As for avocados. I purchase them hard if I do not have a specific use for them. I purchase when they just give under gentle pressure with thumb or finger if I want them in a day or to. I buy them when they give a lot if I want them today or tomorrow. As for the green bags. I put them in the green bag and refrigerate them, taking them out a day or two before I need them to allow them to ripen. If they are browning because I didn't get to them, I simply spoon out the brown parts and toss. But once ripened , avocados have a short shelf life, no mater what one does. I like mashing a bit of lemon or lime juice into the flesh to help it keep. Or a perfect avocado half, pit removed, and cavity filled with balsamic vinegar, eaten right out of the skin with a spoon is pure heaven......
 
Annie August 2, 2020
This is the best avocado tip I've ever received, from a friend who grew up in Mexico: When you open the avocado, set the pit aside. After making the guacamole, put the avocado pit in the bowl with the guacamole; just push it into the center. The surface will not turn brown. Remove the pit just before serving (don't forget to lick off the guacamole). This works even if you made it a few hours before the party or meal and even if you've refrigerated it. This also works if you're only using half of an avocado: leave the pit in the side you're going to store. Just put it in a baggie and refrigerate. No browning.
 
judy August 4, 2020
For me, using the pit to prevent browning fails. I mix in a little lemon juice. I do leave the pit in the half I am not going to use. Put in a baggie, but make sure the plastic complejteladheres to the green flesh around the pit and all the way to the edge of the fruit. That will keep the air off and prevent browning.
 
Adrienne B. August 2, 2020
Here's what I do. I buy a few green Hass avocados and put them in the vegetable bin in my refrigerator. It slows ripening a LOT. I've had them take three or even four weeks to ripen in the fridge. If I want one to eat the next day, I take it out and put it on the counter, hopefully with a banana to help it along. By the time dinner rolls around the next day, that avocado is perfectly ripe. As for the little brown bits, unless they have white on them, we eat them just fine. Also, I don't use lime or lemon with avocado because the flavor is too strong - if I need to keep cut avocado from browning, I put plastic wrap directly on the avocado or guacamole.
 
Dale August 1, 2020
I wish someone would spread the word...to test if an avocado is ripe, lightly press the top! NOT the whole avocado in the middle!!! Drives me absolutely crazy watching idiots squish the hell out of these poor things😩🤬
 
Irene V. August 1, 2020
If I know I will be using avocados for a recipe, I usually buy them a few days in advance and buy them underripe and let them ripen on the counter. That way, I know by the time I need them they should be perfect. If they're ripening too quickly, I put them in fridge. I have only rarely purchased avocados and found them to be rotten when cut.
 
[email protected] August 1, 2020
I so enjoyed the comments, especially by Frank.
I live In Las Vegas, close to California and Mexico. I have bought the bag of small avocados from Costco in the past 3 months, every one nasty, so I threw them out. Albertsons were larger, bought 3, ripened on the counter, then put in the fridge. When I took each out, they were brown and stringy. Threw them out. Sprouts not much better. I bought one large from Trader Joe’s 3 days ago, fingers crossed. I’m looking at the photos of the perfect ripened halved avocados in this article and it’s been a long time since I have experienced one so perfect. Are the good ones going to the commercial businesses and the crappy ones going retail?
 
Kevin K. August 1, 2020
I’ve not had issues with avos from Sprouts - as long as I but them unripe and allow them to ripen at home. Same with TJs - though not the ones in the mesh bags as they’re inconsistent. The best are the loose ones. I shop at the Sprouts on Sahara and Hualapai and the TJs in DTS.
 
Michele August 1, 2020
I read an article about Avocados last year I forget where, sorry. But it said if your Cados are ripe and ready then refrigerate them to prevent them from continuing to ripen or over ripening. I have had excellent results with this strategy.
I also have a question, since oxidation leads to inflammation in the body, is it damaging to your cells if you consume oxidized foods? Unintentionally, of course.
 
Stacy K. August 1, 2020
If they are ripe and ready then EAT THEM
 
Irene V. August 1, 2020
To keep my avocados, once cut, from oxidizing, I wrap them in aluminum foil. Press the foil right up against the flesh, making a smooth seal, and wrap it up (I leave the pit in as well). I don't know the science behind it, but my avocados will stay green for at least a couple of days. Also, if I'm not going to use the whole avocado, I cut it crosswise (not lengthwise) which exposes less of the flesh (and wrap in foil as noted above). Hope these tricks work for you as well.
 
touchofgrey56 August 1, 2020
What if I were to build a hyperbaric chamber in my basement for storing my avocados? Would that help keep them fresh?
 
Jeannine F. August 4, 2020
No. It would have the opposite effect!
 
Stacy K. July 31, 2020
Hey - you didn't really leave the option open for perfect avocado ripeness - I don't want to eat an overripe gray/brown tasteless soft creepy avocado - it was good last week! But I don't want to eat a perfectly ripe avocado that was left out to oxidize and turn brown either - NOPE - I want to eat a perfectly ripe avocado - cut into it and consume it while it is pristine in its flavor and texture and goodness - a bit of yellow/gold and a lot of mellow green - the perfect avocado - not hard to get!
 
Anne J. July 31, 2020
Oy! This is avocados, not blood typing before transfusion. It’s unlikely to hurt you if you eat a little to see if it tastes bad, I have no immune system thanks to ongoing chemo but I still taste them. But, and here is the best advice, pay attention to your fruits. They can stay fine for a long time in the refrigerator which is why I buy mine not quite ripe and bring them out as needed to ripen on the counter. If it isn’t important enough for you to pay attention at the front end to your foods, perhaps you aren’t ready for the responsibility of buying and using avocados. This is really said tongue in cheek but really a lengthy article to a topic which is a very esoteric issue these days.
 
Mar July 31, 2020
Fair enough! You just reminded me that it is way too easy for me to procrastinate // waste time online!

 
Kevin K. July 31, 2020
On the food safety issue: off odors do NOT indicate a food safety problem - despite the “expert” commentary on Food52 - as maleficent bacteria have NO odor. If it smells off it might well taste off - so perhaps pitch it - but it’s not automatically a food safety concern, especially if it hasn’t been cut till now. As for already cut avocados or already made guacamole, scoop off the offending dark stuff. You’re good.
 
Mar July 31, 2020
Keeping a good but cut avacado green has never been a mystery to me - use the citrus acid or spray oil trick. I thought this would be about how to keep an UNCUT avocado good for longer. Avoiding the "not yet, not yet, not yet, not yet, ripe, too bad, it's too late!" phenomenon. They go from under ripe to spoiled in a day. Any tips on prolonging the "uncut window"??
 
RuthAnn July 31, 2020
We buy a bag of very green avocados from Costco almost every week. It seems to take about 3 to 7 days for them to ripen. Do not feel the body of the avocado just test if the top near the stem end gives under slight pressure. If so it is ripe and we put it in the frig and it lasts for several days until cut. This process has worked well for us over the last few years. I would never buy a ripe avocado since frequently it is over ripe when cut.
 
Nikki July 31, 2020
From someone who has a horrible sense of smell, I have learned that if it smells like bacon (yes, bacon!) it's bad. I have come across that look okay, but maybe on their way out, but if they smell like bacon.. toss 'em! I am pescatarian, so the small of raw meat is not appealing to me (although, it wasn't really either when I ate meat) and so this is one way I try to discern if it's good enough to use! Hope this helps, and I also hope I'm not the only weird one who thinks this. Haha!
 
Emilie R. August 1, 2020
Bad avocado doesn't just smell like bacon, it also tastes like bacon. Nasty bacon. Gross!
 
rbrock1225 July 31, 2020
I started doing something years ago when I used to prep materials for business meetings my husband was having at our home and I couldn't be around to help with food. We ended up w/an assortment of deli meats/cheeses and I'd fix platters of fixin's. All he had to do was take stuff out of the refrigerator.

For the avocado, I'd slice avocado, fan it out on a small plate, then spray the surface w/Pam. Pam is just canola oil but provided an barrier to oxygen. The small amount of oil from the Pam is negligible compared to the amount of fat in avocado. Plus it doesn't affect the flavor like lemon/ lime/ onion does

I'd put a bit of plastic over it and it could sit happily for the ~six hours until he served it. Once you started picking at those slices, what was left would brown. Similarly, if I want to fix guacamole for a party, I'll go ahead and do so, spray the surface w/Pam, put some plastic on it (press it directly to the surface), and it can sit for hours.
 
Frank July 31, 2020
I think I understand it even less now that I read this article. This is how I perceive the life of an avocado. Not ripe, not ripe, not ripe, not ripe, not ripe, not ripe,ripe, rotten.
 
pjcamp July 24, 2020
Vacuum seal it.

No air, no oxygen. No oxygen, no oxidation.

Now of course no vacuum sealer makes a perfect vacuum, but it is plenty close enough for there to be little to no noticeable browning.
 
Jill P. July 31, 2020
And in the absence of a vacuum sealer, a tight wrap with Press-and-Seal keeps the avocado mostly green for a few days after cutting. I slice it in half, leave the pit in, use the half without the pit, cover the remainder with the shell, and wrap and refrigerate...
 
Sherry M. July 6, 2020
I am a chef of many years, and this question of how to keep avocados from turning brown has been a mystery to me most of my life until recently. Living in Mexico, I always have a large container of pico de gallo on hand. When I place a half of a cut avocado face up on top of the pico de gallo and cover the container with its lid, the cut avocado does not turn even the slightest bid brown! I am amazed! For those who don't know pico de gallo, it's mixture of fresh diced tomatoes, diced onions, minced jalepeño chili, chopped cilantro, salt, lime juice. I don't know if it is the acidity or the humidity of being enclosed in the container or a combination of the two, but it definitely keeps the avocado perfect for the next few days. Good luck!
 
Beth November 27, 2019
This has been driving me absolutely nuts this year. We get our avocados from an organic grocery store. I generally buy them on the green side and let them ripen slowly at room temperature for a few days until they have a little bit of give to them. More often than not, when I cut them open, they have large areas of browned flesh and I wind up cutting out almost have of the avocado. It's been frustratingly hit-or-miss with avocados this year; some are perfect but many others have had all this ugly browned flesh and strings through them.
 
Beth November 27, 2019
...cutting out Half (not "have") of the avocado. Oops.