The transformation of a green tomato to a vibrant red fruit is a biological process known as ripening. This change involves the degradation of chlorophyll (the green pigment) and the simultaneous production of carotenoids. Carotenoids, such as lycopene, are the red and orange pigments that give the tomato its mature color. The time required for this transition is highly variable and depends on genetics and environmental conditions.
Typical Ripening Timeline
The ripening timeline is measured from the “mature green” stage. This stage is defined when the tomato has achieved its full size and may begin to lose its deep green color, sometimes showing a slight pale break near the blossom end. The tomato must reach this stage before the internal chemical processes leading to color change can begin.
Under optimal conditions, the period from the mature green stage to a fully red, ripe tomato spans 20 to 30 days while still attached to the vine. Larger tomato varieties may take longer to complete this process than smaller types, such as cherry tomatoes.
The appearance of the first blush of color, often called the “breaker stage,” signals that the internal ripening process is irreversible. The fruit is producing the necessary compounds and will continue to ripen even if picked. Any deviation from ideal growing conditions will directly affect this 20-to-30-day period.
Environmental Factors That Influence Ripening Speed
Temperature is the most significant environmental factor controlling the speed and quality of the ripening process. The ideal temperature range for efficient lycopene production (the compound that creates the deep red color) is between 68°F and 77°F (20°C and 25°C). When temperatures fall below 60°F (16°C), the chemical reactions slow down considerably, lengthening the time it takes to turn red.
Temperatures exceeding 85°F (29°C) also hinder ripening, causing the production of lycopene and other red pigments to cease. In these high-heat conditions, the tomato may remain green or develop a yellowish-orange color instead of deep red. This is common during heat waves, where the fruit might stall in the mature green phase.
Ripening is regulated by ethylene, a naturally occurring gaseous plant hormone. The tomato plant produces this hormone, which acts as the internal trigger for color change and softening. Plants under stress from drought or overwatering may produce less ethylene, slowing down maturation.
While light is necessary for the plant to grow, the actual process of color change does not require direct sunlight. Direct, intense sun exposure can heat the fruit beyond the optimal temperature range, inhibiting the production of red pigments. Ambient warmth, rather than direct solar radiation, drives the ripening process.
Techniques for Ripening Tomatoes Off the Vine
When the growing season ends or a frost is imminent, mature green tomatoes can be ripened indoors. The primary goal of post-harvest techniques is to concentrate the naturally produced ethylene gas and maintain a steady, moderate temperature. Only tomatoes that have reached the mature green stage, having attained their full size, will successfully ripen.
One effective method is placing the tomatoes in a brown paper bag or a cardboard box. This enclosed space traps the ethylene gas the fruit naturally emits, accelerating the ripening process. Adding an extra source of ethylene, such as a ripe banana or apple, can boost the gas concentration and speed up the color change.
The tomatoes should be stored in a single layer to prevent bruising and checked frequently for rot. The ideal indoor temperature for this process is around 65°F to 70°F (18°C to 21°C), which is slightly cooler than the vine-ripening optimum. Storing the fruit in a cool, dark location ensures consistent temperature and prevents excessive heat buildup.