What gas makes apples ripen really fast?

Ethylene gas is produced by Apples and can be used to make other fruits, such as peaches, Pears, and tomatoes, ripen quickly.

Have you heard that old saying about one rotten Apple can ruin the whole bunch? That is true, because rotting Apples put out a lot of ethylene gas which speeds up the ripening (or over-ripening) of all of the other other Apples in the bunch.

If you want to speed up the ripening of unripened fruit, just place the fruit in a brown paper bag with several Apples, fold down the top of the bag, and leave at room temperature for a couple of days.

The bag captures the Apples' ethylene gas thus speeding up the ripening process.