To ripen green tomatoes, store tomatoes in an area where the temperature stays around 55 to 60 degrees Fahrenheit and wait approximately one month for them to turn red. To accelerate the ripening process, mix a few ripe apples in with the green tomatoes. Then, when the skin of the tomatoes turns pink, move the tomatoes to a warmer area to complete the ripening process.
Place pink-skinned tomatoes in a bowl or on a single layer on a table for approximately a week so they can ripen. The room temperature should stay between 65 and 75 degrees Fahrenheit. To accelerate the ripening process further, place the tomatoes in brown paper bags with a few holes punched in the sides. This step increases the humidity levels around the tomatoes. Tomatoes placed in a plastic fruit-ripening bowl also ripen more quickly.
Never store green tomatoes in temperatures below 50 degrees Fahrenheit because the tomatoes become soft before they can ripen. Also, do not place ripening tomatoes directly into the sunlight.
Adding apples to the area where the tomatoes ripen increases the amount of ethylene gas in the area. Ethylene gas encourages tomatoes to ripen; commercial growers actually use large amounts of ethylene gas to ripen tomatoes sold in stores.