Yes, a green tomato can successfully complete its ripening process even after being removed from the plant. This technique is often employed by home gardeners facing the end of the growing season or the threat of an unexpected cold snap or frost. By harvesting fruits at the correct stage, you can extend your yield and enjoy homegrown tomatoes weeks after the first freeze. This simple intervention allows the natural biological mechanisms within the fruit to proceed indoors.
The Science of Tomato Ripening
Tomatoes are classified as climacteric fruits, meaning they possess the unique ability to continue their ripening process even after being harvested from the vine. This post-harvest maturation is dependent on the internal production of the gaseous plant hormone called ethylene. Ethylene acts as the biological trigger, initiating a cascade of biochemical changes necessary for full maturation.
The most noticeable transformation is the degradation of chlorophyll, the green pigment, which then allows underlying pigments known as carotenoids to become visible, creating the familiar red, orange, or yellow colors. Simultaneously, the fruit’s texture changes as enzymes like polygalacturonase soften the cell walls. Stored starches are also converted into simpler, more palatable sugars. This complex, coordinated action leads to the sweet flavor and soft texture characteristic of a ripe tomato.
Identifying the Mature Green Stage
The success of indoor ripening depends on harvesting the tomato at the “mature green” stage. A truly immature fruit, picked too early, will likely shrivel or rot instead of successfully ripening. The fruit must have reached its full, intended size for the specific variety being grown before picking.
Visually, the dark green color of the tomato will begin to lighten, often showing a faint pale green or whitish star shape on the blossom end. The skin will transition from a dull, velvety surface to one that appears slightly glossy or waxy. A gentle squeeze should confirm the fruit is firm and hard, indicating the internal seed jelly has begun to form. Harvesting at this moment ensures the fruit has accumulated enough stored energy to complete the climacteric process off the vine.
Techniques for Indoor Ripening
Once the mature green tomatoes are harvested, several techniques can be used to manage the release and concentration of ethylene gas to encourage ripening. One method involves wrapping individual fruits loosely in newspaper or placing them in a single layer inside a paper bag or cardboard box. These enclosures trap the naturally produced ethylene gas around the fruit, accelerating the process.
The placement of the container is important, requiring a location that maintains a temperature range of 65 to 70°F. Temperatures below 50°F will permanently halt the ripening process. Temperatures consistently above 85°F can interfere with color and flavor development. Avoid placing the fruit in direct sunlight, as this can cause the tomato to cook or develop a tough, pale skin.
To accelerate the process, gardeners use companion fruits that leverage high external ethylene production. Placing a ripe banana, apple, or avocado in the same bag or box as the green tomatoes will introduce a surge of the gaseous hormone. These fruits are prolific ethylene producers and their presence can shorten the time required for the green tomatoes to turn red.
Regardless of the method chosen, check the tomatoes every few days and remove any that have fully ripened or begun to show signs of mold or rot. This prevents the decay from spreading to neighboring, healthy fruit. Maintaining a consistent, moderate temperature and monitoring gas concentration are the two main drivers of successful indoor maturation.
Why Some Green Tomatoes Never Ripen
The most common reason for failure is harvesting a tomato that is physiologically immature, meaning it was picked before the “mature green” stage. These under-developed fruits lack the necessary stored energy and are prone to water loss, causing them to shrivel and soften before any color change is observed.
Another inhibitor is storing the fruit in temperatures that are too cold, specifically below 50°F. This temperature threshold permanently halts the enzyme activity required for color development and sugar conversion. Any fruit showing signs of disease, such as dark spots or late blight, should also be discarded, as the disease often progresses faster than the ripening process.