My sister called at four in the afternoon once, mid-panic, because she had promised guacamole for a party and every avocado in her kitchen was a green rock. I talked her through this and the dip made it on time.

Why the paper bag works

Avocados ripen because they give off ethylene gas. A closed paper bag traps that gas around the fruit, so it ripens faster without cooking it. Put the avocados in a brown paper bag, fold the top shut, and leave them on the counter. Check after a few hours.

Want it even faster? Add a banana or apple

Bananas and apples release a lot of ethylene too. Toss one into the bag with your avocados and they should soften within twelve to twenty-four hours instead of several days. I keep a banana in the fruit bowl for exactly this reason.

When you are truly out of time

If you need usable avocado in under an hour, your best move is speed-ripening with gentle heat. Wrap the avocado in foil and set it in a warm spot for about ten minutes, or nestle it next to the toaster oven while it runs. This does not truly ripen the flesh, but it softens the texture enough to mash for guacamole in a pinch. Do not microwave it unless you enjoy warm, mushy disappointment.

What not to do

• Do not squeeze avocados hard to test them. You bruise the flesh and it turns brown inside.
• Do not store ripening avocados in the fridge. Cold pauses the process.
• Do not use a plastic bag. It traps moisture and speeds up rot instead of ripening.

Press gently near the stem. If it gives a little, it is ready. The stem trick never lies: pop the little cap off and if the flesh underneath is green, you are good to go.