You Can Ripen Bananas In Under An Hour, But There's A Catch

Bananas can be a finicky purchase. Without mashing or peeling them right in the store (typically frowned upon by most grocery stores), you have to take a risk with their ripeness. Grocery store bananas are generally set out in their green, unripe state to give them a longer shelf life. But, unless you like green bananas as a snack or you have as many as five days before you need to use the bunch, this can be inconvenient. However, there is a method for satisfying your banana cravings right away — as long as those cravings involve baking.

This particular banana-ripening technique only works when you've got breads, muffins, and banana upside-down cake in mind, because its secret ingredient is raw egg yolk. Serious Eats shared the method after some scientific experimentation, beginning with the understanding that one of the enzyme byproducts of banana ripening converts starch into maltose and glucose (or sugar), which makes the bananas sweeter and more moist. With that chemical process in hand, you can harness the similarly enzymatic power of egg yolks and ripen your green bananas in as little as 30 minutes.

The egg-and-banana mixture works partly because of the chemical makeup of egg yolks and partly because of the chemical process of banana ripening. Bananas are climacteric fruits, which means that they'll keep ripening even after they're picked. As they ripen, they produce ethylene gas that alters green chlorophyll pigments to change the color (which is called enzymatic browning), denatures a polysaccharide called pectin to make the banana softer, and converts the unripe banana's high starch content into sugar to make it sweet. The enzyme that makes that last quality possible is called amylase, and it's also found in egg yolks.

Mixing unripe bananas with the amylase-laden egg yolks will introduce that enzyme and its effects ahead of schedule, artificially speeding up the ripening process and turning bananas from starchy and acidic to sweet and rich in moisture (exactly what you want for baking). Most recipes for baking with bananas will call for eggs already (even a simple three-ingredient banana bread), so you probably won't have to change the necessary ingredients. All you'll need to do is mash the bananas with just the raw eggs and wait about 30 minutes. The best ratio is one egg yolk to one medium-sized banana, which is usually around four ounces. If that ratio doesn't line up with your recipe and you have too much banana, you can lengthen the waiting time or add more eggs.

Incorporating the amylase enzyme into your unripe bananas is quick and effective, but it's only useful if those bananas are part of a recipe (since raw eggs rarely make a good snack). There are other ways to circumvent nature, though, and ripen bananas in a pinch, but each has its place. If you have a couple of days to spare or your primary purpose is snacking, you can stick bananas into a paper bag with a ripe, climacteric fruit that will produce ethylene, like a peach or avocado. The ethylene production of the ripe fruit will speed up the banana's own ripening process, and it will go from green to yellow in only about two days.

Other ripening solutions are, like egg yolks, best used for baking because they change the banana's texture. The oven works quickly — just set skin-on bananas in a 250-degree-Fahrenheit oven for about 5–10 minutes. The skins will darken, and a green banana's firm interior will get soft. If you leave them in the oven for longer, the sweetness will become more pronounced. The microwave works even faster, but you'll have to forgo the sweetness since there's no starch conversion taking place. Just peel the banana, make some holes with a fork, and microwave for about 30 seconds or until you get the soft texture. You won't get all-inclusive artificial ripening like you would with eggs, but these methods are better suited to eggless recipes.