Does submerging an avocado in water keep it fresh? The science behind the hack

There seems to be no reliable calculus for timing an avocado’s ripeness. One day the fruit seems rock hard and the next it's squishy shades of brown.

An online hack boasts a way to suspend the ripening process for avocados, lemons, limes, and other produce. According to the hack, all one must do is submerge the produce in water and store it in the fridge. Then, produce can stay young for weeks. Is it too good to be true?

Rutgers University food scientist Karen Schaich — who tested the idea out herself — tells Inverse why, even if it works, it still might not be a good idea.

Do fruits and veggies stay fresh submerged in water?

According to those who have tried this technique, avocados can be submerged whole while unripe, and even weeks later, the inside remains a pale green. Another amateur food scientist claims lemons and limes can store for up to three months in water.

Karen Schaich explains her take on this technique. “Everybody on the web says, ‘Oh, it's because it keeps the oxygen out,’” she tells Inverse. “But that’s only one part of browning.” Browning is the oxidation reaction that causes some fruits and vegetables to turn brown.

This method of storing doesn’t prevent oxidizing as much as it does slow ripening. For example, fruits that have been cut open can brown and oxidize as oxygen reaches them and breaks down superficial tissue. But while ripening fruits can turn brown, that’s a different chemical process.

Part of this depends on whether the fruit is climacteric, which means that the fruit ripens after harvest and after separation from its parent plant.

Some climacteric fruits:

• Apples
• Peaches and nectarines
• Avocados
• Pears
• Mangos
• Bananas
• Apricots
• Plums
• Blueberries
• Cantaloupe

And some non-climacteric fruits:

• Citrus fruits such as lemons and grapefruit
• Strawberries
• Raspberries
• Cherries
• Grapes
• Pineapple

The compound responsible for ripening in climacteric fruits is a gaseous plant hormone called ethylene. There’s an initial concentration of ethylene in fruit, which boosts further ethylene production. This type of process is known to be “autocatalytic”. So as ethylene production starts, the molecule comes in droves. “Those are all enzymatic changes, and some of the messages that tell the fruits they should be breaking down the starches into sugars and producing flavor compounds are triggered by the production of ethylene,” Schaich says.

Schaich thinks that submersion in water slows this ethylene production, which halts ripening. On the other hand, non-climacteric produce, such as lemons and grapes, won’t continue to ripen, but storage in water keeps them from dehydrating quickly. To her, however, the method doesn’t seem viable for days or weeks.“I have never had a fruit or vegetable that I could put very long in water without it becoming waterlogged because these tissues pick up water,” Schaich says. She finds it “extremely difficult to believe” that water wouldn’t permeate the skin, even of an avocado’s tough exterior.

To appease her curiosity, she tried this method herself using a lemon (non-climacteric, so it stops ripening once picked) that was already several weeks old. She had been storing it in a mesh bag, and while it was a little dehydrated there were no signs of “microbial or biochemical spoilage,” she says. She stored it in a container of water in the fridge for nine days.

Just a day after the experiment began, she noticed the lemon had absorbed water and swelled, with a hydrated, firm rind. “The lemon actually looked like it had been ‘restored,’” she writes to Inverse, concluding that water restores dehydrated lemons as quickly as within a few hours. The reason the lemon absorbs water, she says, is to balance dissolved molecules; there was a far higher concentration of dissolved molecules in the lemon than in the surrounding water. The water enters the rind’s pores to balance the ratio of water and dissolved particles both in and outside the lemon.

At this point, she wondered if eventually absorption would stop and the rind would stay supple. The lemon continued soaking for several days, continuing to swell with an intact rind. “At this point, I wondered whether the lemon would swell to bursting,” she writes. “To my surprise, eventually the lemon swelling stopped.” She turned her attention to the rind to see if it would change at all now that it stopped taking in water. After five days, she describes the lemon as feeling softer. “The squeeze was still firm but the rind began to lose some of its stiffness,” she writes to Inverse.

To truly test the experiment with all senses, she juiced and tasted the lemon. “The rind was definitely softer and tore easily at the edges,” she writes. The water the lemon had soaked in had taken on a “light lemon taste, which could have resulted from some terpenes” — natural chemical compounds in plants responsible for flavor and aroma — “migrating from the peel.” The juice itself, she says, was much more sour than usual, which she attributes to some sugars and flavor compounds leaching from the lemon into the surrounding water to balance the concentration of dissolved molecules. She concludes that had this lemon continued soaking, the rind would have continued to soften. “[There] is definitely a useful time limit for this method,” she writes.

Why it's probably not a good idea to submerge your produce in water

Safety is also a potential complication. “You cannot keep bacterial contamination out of the water, even if you wash [the produce] in a bleach solution before you put it in water,” she says. One way to reduce possible contamination risk is by boiling the water first, but it could still be contaminated by anything floating around your kitchen or refrigerator.

There’s also the issue that microorganisms already living on the produce’s surface might not get completely scrubbed with water or bleach. Listeria monocytogenes and Salmonella are just a few culprits that can give you some nasty food poisoning. Listeria bacteria can still grow at refrigerated temperatures, so soaking produce in a listeria-laced bath means the germs can multiply, and even infiltrate the avocado.

“Microorganisms that are in the water can pass in through the pores on the outside and they can get into the tissues,” she describes. “So it is not a practice that I would recommend.”

What is the best way to store produce?

Water and avocados actually do work at keeping these fickle fruits from oxidizing. If you’ve made a batch of guacamole, Schaich recommends filling a container with it and then topping it off with a thin layer of water and perhaps some lemon or lime juice. In this case, the water slows oxygen from reaching the guacamole and further breaking down the compounds into brown mush. The fattiness of the avocado will keep the water from seeping into the mixture.

If you have wilted lettuce or other leafy greens, soaking them for a bit in water can help revive them, too. But again, leaving them in water for too long will probably result in waterlogging, so make it quick. And, as Schaich has learned, giving a lemon an overnight bath can also revive it.

Editor’s Note: This story has been updated with new information from Karen Schaich.

CHECK, PLEASE is an Inverse series that uses biology, chemistry, and physics to debunk the biggest food myths and assumptions.

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