To get green tomatoes to ripen to a red color, store them in a location that is between 55 and 60 degrees Fahrenheit for about a month. This technique also works with tomatoes that have a blended green-and-pink coloring.
- Pick the tomatoes
Tomatoes from new plants respond better to the indoor-ripening process than those that come from more mature plants. Pick healthy, undamaged tomatoes before the first frost.
- Prepare the tomatoes
Cut off the stems, which can damage the tomatoes when they are stored closely together. Remove any tomatoes that are already close to ripening because their proximity to the green tomatoes causes bruising.
- Store the tomatoes
Place the green tomatoes in a location that remains a consistent 55 to 60 degrees Fahrenheit. Temperatures below 50 degrees Fahrenheit cause the tomatoes to soften before they ripen. Do not place the tomatoes in a refrigerator. When the skins become pink, move the tomatoes to a warmer location to finish ripening.
- Speed the process
The normal ripening process takes a few weeks. If you want the tomatoes to ripen faster, mix some apples in with the green tomatoes. Both the tomatoes and the apples emit ethylene gas, which causes the tomatoes to ripen. Adding the apples increases the amount of ethylene gas being emitted, speeding up the ripening process.