The transition of a tomato from green to red involves a complex biological process influenced by the plant’s internal signals and the surrounding environment. The exact time frame is highly variable, depending on factors like the tomato variety and prevailing weather conditions. Understanding this process helps gardeners manage expectations and maximize the harvest.
Typical Ripening Timeline
The ripening process begins once the tomato reaches its full, mature size, known as the mature green stage. From this point, the average time required for the fruit to fully transition to a deep red color typically falls within a range of 20 to 30 days. This conversion period can be shorter for small-fruited varieties, such as cherry tomatoes, and longer for large beefsteak types.
Ripening occurs in distinct phases, beginning with the “breaker stage,” where a faint pink or yellow blush appears on the blossom end of the fruit. This initial color change signals that the fruit will continue to ripen even if it is picked from the vine. The tomato then progresses through the turning, pink, and light red stages before reaching the final, fully ripe stage.
The Role of Ethylene in Color Change
The entire ripening sequence is orchestrated by the plant hormone ethylene. Ethylene acts as a signaling molecule that initiates internal changes once the fruit reaches physiological maturity. It is responsible for triggering the shift in the fruit’s pigment production.
Ethylene’s first action is to break down chlorophyll, the green pigment responsible for photosynthesis. As chlorophyll disappears, the fruit synthesizes and accumulates carotenoids, which are responsible for the red and yellow colors. The most prominent of these is lycopene, the compound that gives red tomatoes their characteristic hue. The concentration of lycopene can dramatically increase as the fruit moves from green to fully ripe.
External Conditions that Affect Ripening Speed
The speed and success of the color change are sensitive to external environmental factors, with temperature being the most important influence. The enzymatic conversion of pigments is most efficient within a specific temperature band. The ideal range for maximum lycopene production is between 68 and 77 degrees Fahrenheit (20 to 25 degrees Celsius).
Temperatures outside this optimal range inhibit the process, causing the fruit to stall in the green or yellow stage. If the temperature consistently rises above 85 degrees Fahrenheit (29 degrees Celsius), lycopene synthesis is significantly reduced or stops entirely, resulting in tomatoes that stay yellow-orange instead of turning red. Similarly, temperatures dropping below 50 degrees Fahrenheit (10 degrees Celsius) also inhibit the necessary pigment enzymes, stalling the ripening process.
While warmth is necessary, direct sunlight is not required for the fruit to develop its red color. Intense, direct sun exposure can sometimes lead to sunscald or toughen the tomato skins. The color change is a chemical process driven by the fruit’s internal temperature, not by exposure to light. Other factors, such as inconsistent watering or an excess of nitrogen in the soil, can also stress the plant and indirectly slow the fruit’s maturation.
Techniques for Ripening Tomatoes Indoors
When the growing season nears its end, or if temperatures become unfavorable, mature green tomatoes can be ripened indoors. The best candidates are fruits that have reached the mature green stage (characterized by a slight shine and full size) or those already showing the first blush of color, known as the breaker stage. Tomatoes picked at the breaker stage will achieve a flavor nearly comparable to a vine-ripened fruit.
A common method is to place the tomatoes in a brown paper bag or a cardboard box. This container traps the ethylene gas that the tomatoes release as they ripen. To accelerate the process, a ripe banana or apple can be added, as these fruits are prolific producers of ethylene.
The container should be kept at room temperature, ideally between 68 and 75 degrees Fahrenheit, and out of direct sunlight. Tomatoes stored in warmer conditions will ripen in a few weeks, while those kept on the cooler side of this range will take up to a month. Fruit exposed to temperatures below 50 degrees Fahrenheit will ripen slowly and develop a bland, mealy texture.