Pick tomatoes when they are greenish-white and full-sized. Make sure they are firm and solid before harvesting.
Pull the stems off the green, unripe tomatoes and rinse in cool water to remove soil or grime. Thoroughly dry the tomatoes with a towel.
Place the unripe tomatoes in a clean, brown paper bag. Put a ripe apple in the bag along with the unripe tomatoes. Ripe apples emit ethylene gas, which naturally speeds the ripening process in tomatoes.
Fold over the paper bag's opening to prevent the ethylene gas from escaping. Store the closed paper bag on your kitchen countertop.
Examine the tomatoes daily to check the ripening process. The tomatoes are ripe when they are red and slightly soft. Tomatoes generally ripen in one to five days, depending on when they are harvested.