reaches a full size and the fruit becomes a pale green, it begins the ripening process. After the tomato reaches a stage when it's about ½ green and ½ pink, a layer of cells forms across the stem of the tomato- sealing it from the main vine. At this point there is nothing moving from the plant into the fruit. At this stage the tomato can be harvested and ripened off the vine with no loss of flavor, quality or nutrition.

Red pigments in tomatoes don't form above 95°F so tomatoes ripened in extreme heat will have a orange-red color. Tomatoes held indoors at cooler temperatures will ripen slower. You can speed up or slow down the ripening process by raising the temperature (to an optimum of 85°F) or lowering the temperature (to a minimum of 50°F). Tomatoes develop their optimum flavor, nutrition, and color when the tomato is in the full red ripe stage but this doesn't have to occur on the plant!