We've all been there: The supermarket only has hard, unripe avocados but you're craving guacamole or avocado toast NOW. The internet claims that instant gratification can be yours if you simply wrap an unripe avocado in foil and put it in a preheated 200 degree oven for 10 minutes. Presto: ripe avocado.
I was skeptical. I imagined warm, mushy, baked avocado. But there did seem to be good reasoning behind the technique: Fruits like avocados and bananas release ethylene gas as they ripen, and the presence of the gas speeds ripening. (That's why putting a ripe banana in a bag with an unripe avocado will ripen the avocado in a day or so.) Apparently when you wrap the fruit in foil and warm it, the avocado releases ethylene, the gas is trapped under the foil, and ripening happens lightning-fast.
A similar trick works for speed-ripening bananas for when you simply must have banana bread but have only sad, green bananas.
So I decided to try it. I started with this unripe avocado.
It was definitely not ready to eat: Light-medium green and hard. Probably a day or two away from perfection. I wrapped it in foil and put it in a preheated 200-degree oven for exactly 10 minutes.
When I took the avocado out of the oven, the foil was warm to the touch. The avocado itself was barely warm, and it was definitely softer than before. I cut it open and found that the flesh, while still on the firm side, was definitely spreadable. Also, the flesh itself was hardly warm at all, which made me happy. So I did what anyone would do: I made toast.
The avocado still tasted...green. A little flat, not as buttery and wonderful as usual. But the difference is subtle. I think if I had seasoned it with lime juice, chile, and onion to make guacamole, I probably wouldn't have noticed. But this trick is not ideal for simple preparations that are all about the avocado flavor. Also, I've read that avocados that are really rock hard, days and days away from ripe, can take up to an hour to "ripen" in the oven. I would not recommend that—you're going to end up with a baked avocado, not a ripe one.
Final Verdict: Does it work? Sure, if you have an almost-but-not-quite ripe avocado, pop it into a low oven for a few minutes to soften it. But don't expect magic.