Ripening does not truly begin until the tomato reaches the “mature green” stage, which is when the fruit has reached its full size but has not yet shown any color change. The transition from green to the final color is driven by a complex interaction of internal plant signals and external conditions. The duration of this transformation is highly variable, depending mostly on the specific variety being grown and the environment surrounding the plant.
The Typical Ripening Timeline
Once a tomato reaches its full mature size on the vine, the transformation from its initial green color to the final red typically takes a period of 20 to 30 days. This timeframe represents an average, and specific varieties may ripen slightly faster or slower based on their genetics. The ripening process is a gradual journey marked by distinct stages of color change.
The first visible sign is called the “breaker stage,” where the fruit begins to show a definite break in color from green to a yellowish-pink hue, usually near the blossom end. Following the breaker stage, the fruit progresses through the “pink” stage when roughly half of the surface shows color. Finally, the fruit moves into the “red” stage when the color covers more than 80% of the surface. Even at the mature green stage, the fruit has developed enough to continue ripening off the vine, though it will not develop the exact same flavor profile as a vine-ripened tomato.
The Chemistry Behind the Color Change
The shift in a tomato’s color is the result of a coordinated biochemical process within the fruit. The initial green color is due to high concentrations of chlorophyll, the same pigment responsible for photosynthesis in leaves. As ripening begins, the fruit starts to produce the plant hormone ethylene gas, which acts as the primary molecular trigger for the ripening cascade.
Ethylene signals the plant to cease photosynthesis, leading to the rapid degradation of the green chlorophyll pigment. Simultaneously, the fruit begins the synthesis of new pigments, primarily lycopene, a type of carotenoid. Lycopene is an antioxidant compound that accumulates in the fruit’s cells, giving the tomato its characteristic red color. The gas released by one fruit can encourage the ripening of nearby tomatoes.
Environmental Factors That Influence Ripening Speed
Temperature is the most significant external factor controlling the speed of the color change. The optimal temperature range for the enzymes responsible for lycopene production falls between 68°F and 77°F (20°C to 25°C). Within this range, the chemical reactions proceed efficiently, leading to a vibrant red color within the typical timeframe.
When temperatures consistently rise above 85°F (29°C), the synthesis of lycopene pigment is effectively halted, even though the fruit may continue to soften. This is why tomatoes often remain green or turn a pale orange during periods of intense summer heat. Conversely, consistently cool temperatures below 60°F (15°C) also significantly inhibit the ripening process and slow the color change. While sunlight is needed for the plant to mature the fruit, direct sun exposure is not required for the color change itself, and can even cause sunscald if too intense.
Techniques for Ripening Tomatoes Indoors
When conditions on the vine are no longer suitable, such as before an expected frost or during a heat wave, mature green fruits can be successfully ripened indoors. The fruit must have reached the mature green stage—full size and firm—for this method to work, as immature fruits will not ripen. A simple technique is to place the picked tomatoes in a single layer inside a paper bag or a cardboard box. This container traps the naturally released ethylene gas, which speeds up the ripening process.
To further accelerate the color change, a highly ethylene-producing fruit, such as a ripe banana or apple, can be placed inside the container with the tomatoes. The added ethylene concentration quickly triggers the shift from chlorophyll breakdown to lycopene synthesis. The indoor ripening environment should be kept at a warm room temperature, ideally around 70°F, and away from direct sunlight for the best results.