Pick the best produce with these science tricks

If you’ve ever stared at a pyramid of watermelons and just grabbed the one on top, keep reading. You and your probably-subpar fruit could use a lesson or two in how to select the ripest, juiciest melon at the market.

Produce selection is one of those valuable life lessons most people never get. And honestly, a lot of folks don’t even know what they’re missing. If you didn’t grow up eating fresh summer corn picked that morning, peaches plucked right off the tree, or strawberries you harvested yourself, you probably don’t know how great fruit can taste. Lots of grocery store stock won’t ever taste as good as the haul you’ll get from a farmer’s market (or, better yet, at the farm itself), but a little know-how can help you find the best of the lot—and understand when to skip out.

This seems like where we should start, but it’s actually one step too far. First, we have to define what a fruit is, that will help you understand why we’re not also going to talk about how to pick out ripe vegetables.

Scientifically and botanically speaking, fruits are reproductive bits—they’re how plants spread their seeds. Vegetables are, basically, everything else. When you chow down on asparagus or some nice, crunchy iceberg lettuce, you’re eating a part of the plant nature didn’t really intend for you to eat.

“Their ultimate goal is to produce a seed, but humans came along and modified it, and said let’s make the leaves lush, and soft, and tender,” says Marvin Pritts, a professor of plant science at Cornell’s College of Agriculture and Life Sciences. “The original species wasn’t that good—it was edible. We’ve made it taste good.”

Because vegetables are somewhat artificially produced for humans, it’s not a guessing game to know when exactly the product will be ready. Once they’re the size you want, you can pick them.

“Farmers don’t harvest vegetables until they’re ready, and then it’s just a race against time,” says Patrick Ahern, who’s one of the folks in charge of buying produce for Baldor Specialty Foods, one of the largest fresh produce distributors in the Northeast. “Every minute after that, it gets worse.”

Ahern's advice for the best veg is to buy it as close to the source as possible and to eat it right away (or store it properly if you need to save it). It's a good sign if greenery is still attached to veggies like carrots, since it's a clue that the produce was harvested within the last few days (Ahern says this is why high-end chefs often only buy carrots with the tops still on). But overall, vegetables will keep a lot longer and better than any fruit.

This brings us back to what the heck a fruit does when it ripens. A plant’s ultimate goal for its fruit is to get you to eat it, since for millions of years “you” were an animal who was going to poop out the seeds, thereby spreading the plant around. We’ve interrupted that chain with our newfangled sewage systems, but plants haven’t figured that out yet. They still produce fruits that are luscious and ready to eat precisely as the seeds become mature. Pitts says up to 10 percent of a plant’s genes are for controlling ripeness, which is a tribute to exactly how complex and important the ripening process is.

As a fruit grows, it accumulates nutrients, water, and, in some cases, starch, but it stays green to blend in with surrounding leaves until the seeds are mature. Only once it’s ready to be eaten will the chlorophyll break down, revealing the true color underneath. Simultaneously, the starches will change into sugars and the fruit will begin producing aromatic compounds, which give it its characteristic flavor. That’s ripening.

A century ago, kids used to get oranges for Christmas. That may sound like a poor gift now, but at the time, it was special—oranges were only available in winter. As time went on, researchers and farmers developed incredibly clever ways to ship produce around the world year-round, giving us lucky folks in the developed world access to most fruit whenever we want it. But as we’ve bred plants for storage and appearance, Pritts laments, we’ve lost a lot of flavor.

The American supply of strawberries, for instance, is grown almost exclusively in California. If you picked those berries at optimal ripeness, they’d spoil before they got to the East Coast. So farmers harvest strawberries a little early, when they’re hardy enough to withstand the shipping. Normal, wild strawberries wouldn’t turn red off the vine, so farmers today use varieties bred to blush even after they’re picked.

But here’s the problem: some fruits can’t really ripen after they’re picked. Strawberries, peaches, and many other fruits don’t store starches, so they have to remain attached to the plant to produce the optimal levels of sugars. If you pick ‘em too early, they’ll contain some sugar, but no amount of leaving them on the counter will help them develop a better, sweeter flavor. That’s why nothing compares to a tree-ripened peach.

Other fruits, like apples and bananas, do stockpile starches, and can thus be ripened in storage. Bananas are exclusively picked green, shipped, and then exposed to ethylene gas at their destination to ripen them. Ethylene gas is a kind of chemical trigger for a lot of so-called climacteric fruits—it gets the ripening process rolling. Farmers and distributors can withhold ethylene until exactly the right moment, ensuring consumers get a perfectly ripe product. It also means these fruits will ripen on your kitchen counter, since they produce small amounts of ethylene themselves.

Here’s a TL;DR for those of you who scrolled down to get to the goods: some fruits will ripen nicely in your kitchen, while others won’t ever develop a better flavor. Knowing the difference—and understanding the signs of a ripe fruit—will help you know when the off-season stuff just isn’t worth it. Here’s what Ahern looks for in good produce:

For all melons, you want the one that “feels heavier than it looks,” Ahern says. He admits that may be hard for someone who has little experience weighing produce in their hands, but the idea here is to select the densest melon. Pick a few up and see how they feel. The sweetest one will be particularly heavy for its size, since heft is a sign that the melon contains a lot of water. As they ripen, melons (and a lot of other fruits) accumulate water as they develop sugars and other aromatics, so a heavy specimen was likely ripened on the plant—which means lots of flavor.

You can also rap your knuckles on a watermelon to help you out here, since a nice hollow sound indicates more water content. Watermelons ripened on the vine will also have a large yellow spot where they were touching the ground. If the spot is white, though, it’s not ripe yet.

The same heft principle applies here, but the yellow spot and knocking tricks don’t. Instead, look for a melon that has a little bit of give on the bottom (opposite the stem) where the flower was attached. Ideally, it should also be a little bit sticky at that end and have a nice aroma at the stem. Cantaloupes and Galia melons should have defined netting (that rough pattern on their skin), and, in general, the best melons will have the most intense color. Those that don’t have a bright hue when ripe should simply be less green.

Like a good melon, a nice citrus will feel heavier than it looks. A light piece of fruit either means it was picked before it was ripe or that it’s been sitting around a long time, since it’ll dehydrate as water evaporates through the skin.

They say knowledge is understanding that a tomato is a fruit, and wisdom is knowing not to put one in a fruit salad. We’re here to tell you that true enlightenment is realizing redness is not a sign of a ripe tomato. You could expose a bright green tomato to ethylene and turn it a juicy red. What you can’t fake is the tomato smell, so bring one up to your sniffer and get a whiff of the stem end. If it doesn’t smell like a tomato, it’s not ripe. If it has a nice aroma, opt for one with a little give to it, but without too much smush, and definitely not any black specks or crinkly age lines, since those all indicate an overripe tomato.

This trendy fruit actually can’t ripen on the tree, making it a boon for both avocado farmers and you. Though they reach peak ripeness for only a brief time, you can tell by brushing the calyx—the bit that looks like a tiny stem. If the calyx comes off easily, the fruit is nice and ripe (though if there’s brown underneath, it’s probably overripe). If the calyx doesn’t come off, it’s not ready yet. You can also check out the color, which should be a deep green, assuming you’re eating a Hass. If you want to squeeze it, you can, since a ripe avocado will have a little give to it, but Ahern doesn’t recommend this because it’ll cause bruising when the fruit does ripen.

One hot tip: try looking for ones at the bottom of the pile, where ethylene has a better chance of building up (just make sure they haven’t been crushed by those on top). If you really can’t find one, toss hard avocados in a paper bag, maybe even with a banana, to trap the ethylene and prompt ripening.

Pears are like avocados in that they’re only ready to eat for a very short period of time. Buy them hard and as blemish-free as possible—any spots will turn brown once ripe—and let them sit on your counter until they start to charge color (green varieties, unfortunately, don’t change much, so it’ll be harder to tell). Once ripe, they’ll have a little give to them, though Bosc pears will be a bit harder than others. Ahern also says that although he prefers to buy local for almost everything, pears from nearby farms often just get tossed into a box. It’s usually the fruit from pear-producing areas like Washington, which package their produce carefully, that often yield the best bruise-free pears.

Since apples are picked pretty much at peak ripeness and kept in cold, ethylene-controlled storage until they’re ready for the grocery store, you really just want an apple that’s as blemish-free as possible. With non-green varieties, you’re also looking for a bright color.

Pretty much all berries are picked only when ripe, so for everything except strawberries you’re basically making sure you don’t have many rotten pieces. Turn the container around in your hands and take a peek at the bottom to make sure you don’t see (or feel) mushy bits. With strawberries, the best indication is a pleasant odor—you can smell ripe strawberries from a distance.

There are tons of varieties of mangoes, but the ones we get in the U.S. pretty much universally start off green and turn yellow or red as they ripen. You’re looking for as much color as possible, as well as a little give when squeezed, and a nice mango aroma.

The key here is smell, especially with peaches. Neither fruit ripens well off the tree, so don’t bother buying rock-hard versions. They’ll soften in your kitchen, but they won’t develop any more flavor. If you can find a plump peach, make sure it’s as blemish-free as possible.

Again, smell is key. A good pineapple will smell like one, and the skin should have a more yellow tint rather than pure green. Another good test: try to pull out the leaves at the top. If they come off easily, that’s a good sign it’s ripe.