Why are some banana peels grayish?

“If you cut the banana in half you’ll see a bunch of little black spots, which is the end of the strand that you cut through. The vascular strands are what carry the liquid from the plant into the fruit,” Brecht said. 

How do cold temperatures cause discoloration in bananas?

Bananas, as tropical fruit, don’t do well in chilly temperatures. At 56 degrees Fahrenheit or less, a banana won’t ripen properly. It will eventually collapse into mush as its cells break down.

Chilly temperatures cause liquid fats in membranes in banana cells to solidify (like butter in a fridge). This messes up the cells’ plans in a variety of ways, including making those membranes leaky and causing compounds that are normally kept separate to mix. Add in some oxygen and this leads to a series of reactions that produce brown and black discoloration. (The damage inflicted by cold temperatures triggers the same sequence of color-changing events as when a banana or other types of produce, like apples, avocados, potatoes, are cut, bruised or otherwise hurt and turn varying shades of brown and black.)

But even before the banana discolors, you may also notice that a banana or other fruit injured by cold is less fragrant. This is because the enzymes that help generate the alluring aromas central to the ripe fruit are inactivated by the cold. Those enzymes are normally enveloped by protective liquid fats, ready to be deployed as ripening proceeds, but when those fats solidify in a chilly environment they essentially lock up the enzymes in “icebergs” of fat, Brecht explained. 

Will a grayish banana ever ripen properly?

Maybe! Sometimes chilling injury is literally only skin deep. 

“The less severe the chilling injury, the more likely it’ll be able to recover and ripen and be edible,” Brecht said. But “the farther and farther the chilling injury goes the more likely the fruit won’t be able to complete ripening at all.”

Brecht said it’s possible the banana can bounce back once it returns to room temperature. I’ve eaten a number of grayish bananas (likely because my grocery store or their banana supplier stored the fruit too cold) and have usually found them to be just fine for my banana-eating needs. If a banana is simply a little dull or grayish, I say you should go for it. 

Another weird trick of chilling injury is that the damage it causes may not be immediately obvious. The gray color often doesn’t show up until after the bananas return to room temperature. Brecht said that’s because the colder temperatures slow reactions down. So the damage occurs in the cold, but isn’t “processed” until the fruit warms up.  

But…is it ever OK to put bananas in the fridge?

If you put an intact banana in the fridge, its peel will eventually turn an inky brownish black color. What this means for the inside of the banana depends, however, on how ripe it was when you put it in the fridge. 

Unripe bananas should never go in a consumer fridge, which should be set to 40 degrees Fahrenheit or less. They won’t ripen. 

Bananas that are farther along in their ripening journey, however, are less sensitive to chilling injury. If your bananas are perfectly ripe and you want to hit pause before they veer into banana bread-level overripe, then refrigeration will keep them in the perfectly ripe zone for longer, likely for a couple days. During that time, however, the peel may still darken. But below it you should find perfectly ripe banana. The peel, Brecht noted, is actually more sensitive to the cold than the ripened fruit below it. 

Still, if you wait too long, the banana will continue to age and degrade. Whether it’s in the fridge or on the counter, the flesh will eventually collapse into mush and turn brown and black.

How long in the fridge until a banana shows signs of chilling injury?

It can take anywhere from a few hours to a few days, depending on the type of banana, how mature it is and the temperature, according to the University of California’s Postharvest Research and Extension Center. 

Chilling injury in bananas is very common, Brecht said. “The lowest safe temperature is 57, 58 degrees, but they ripen at 60, 62 degrees so their best ripening temperature and the lowest temperature they can tolerate are quite close. You can measure exposure time in hours for what it would take for them to start showing chilling injury.”

Between harvest, shipping and the store, produce companies try to keep bananas as cool as possible, without dipping into temperatures that will damage them. While too-cold temperatures are a problem, cool, but warm enough temperatures slow cellular processes and stall microbial growth—those are good things that can extend the food’s shelf life. 

“There’s a lot of fruit that are chilling sensitive,” Brecht said. “If it’s a species that evolved in tropical or subtropical parts of the world, it never had to deal with low temperature. And now when we handle things postharvest, lowering the temperature is the No. 1 thing that you do to maintain the quality and make them last longer. So, the handlers are always trying to hold the fruit at the lowest temperature they can to get the most of that benefit and sometimes it goes to too low a temperature for that sensitive fruit.”