Tomato ripening is the biological process where the mature green fruit transitions into the colorful, soft, and flavorful edible stage. This transformation occurs after the initial growth phase, which takes 40 to 50 days after the flower is pollinated until the fruit reaches its full size. The total time required for a tomato to reach full ripeness after flowering typically ranges from four to eight weeks, depending on environmental conditions.
The Science of Ripening: Hormones and Color Change
The ripening process is primarily controlled by the gaseous plant hormone ethylene, which initiates the transformation. Tomatoes are classified as climacteric fruits, meaning they produce a burst of this hormone at the beginning of the ripening phase. This hormonal surge triggers internal changes, including the softening of the fruit’s flesh due to the breakdown of cell walls. The most visible change is the shift in color from green to red, resulting from pigment biochemistry. Ethylene accelerates the degradation of chlorophyll (the green pigment), while the fruit synthesizes and accumulates carotenoids, most notably lycopene, which is responsible for the characteristic deep red color.
External Factors Influencing Ripening Speed
Temperature is the most important environmental factor influencing the speed and quality of ripening. The biochemical reactions that produce the red pigment lycopene occur optimally between 68 and 77 degrees Fahrenheit. When temperatures exceed 85 degrees Fahrenheit, the production of lycopene and other carotenoids slows down significantly or stops completely. Extended periods above 90 degrees Fahrenheit inhibit enzyme activity, causing the fruit to remain yellowish-green or pale. Conversely, temperatures below 50 degrees Fahrenheit halt the process by inhibiting the enzymes responsible for pigment production.
Light exposure plays a less direct role than temperature. Tomatoes do not require direct sunlight to ripen once they reach the mature green stage. Intense direct sun can cause the fruit to overheat, inhibiting color-producing enzymes and potentially resulting in sunscald damage.
The inherent genetics of the plant also dictate the timeline, as different varieties have distinct days-to-maturity. Early-season varieties are bred to ripen more quickly than late-season varieties under the same conditions.
Ripening Off the Vine
A tomato must reach the “mature green” stage before it can successfully ripen after being picked. At this point, the fruit has finished growing in size and contains sufficient internal ethylene to complete the process, even when separated from the plant. This technique, known as storage ripening, is often used when frost is imminent or at the end of the growing season.
To encourage post-harvest ripening, store tomatoes at room temperature, ideally between 60 and 75 degrees Fahrenheit. Placing mature green or blush-stage tomatoes in a closed container, such as a brown paper bag, traps the naturally emitted ethylene gas. Adding a high-ethylene fruit, like a ripe banana or apple, can further accelerate the process. Mature green fruit may take one to two weeks to fully ripen, while fruit that has already begun to blush will ripen much faster. Avoid refrigeration, as the cold temperature stops ripening and destroys the fruit’s texture and flavor.