How to Ripen Tomatoes
Here’s a way to ripen green tomatoes that aren't quite at their juicy, peak ripeness or that you’ll have to pull off the vine before the first frost.
Ethylene gas is crucial for ripening fruits like tomatoes and peaches, so giving them a boost of gas when they're not quite at their peak can help speed up the ripening process. Place green tomatoes in a paper bag along with an apple. The apple produces ethylene gas which helps speed up ripening.