A sudden, unexpected frost can bring a swift end to the tomato growing season, often leaving a gardener with a substantial harvest of fruit in various stages of development. Freezing temperatures cause water inside the tomato plant’s cells to expand, rupturing the cell walls and stopping the fruit’s maturation process. Fortunately, frost-damaged plants do not necessarily mean a ruined harvest. A significant portion of the fruit can often be salvaged with prompt action and proper handling. The key lies in quickly assessing the damage and applying specific techniques tailored to the fruit’s ripeness level.
Immediate Assessment of Frost Damage
The priority following any frost event is to harvest all remaining fruit immediately, regardless of color or size, because even a light freeze compromises the fruit’s future quality. Look for visual signs of damage, which often manifest as dark, water-soaked spots on the skin or a translucent, bruised appearance near the stem end. This soft, water-logged texture occurs as ice crystals form and then thaw, causing the cellular structure to collapse.
If the temperature drops low enough for the fruit to freeze solid, the damage becomes extensive. A completely frozen tomato that thaws will become mushy and flavorless due to deep cellular destruction. Furthermore, exposure to cold temperatures below 50 degrees Fahrenheit can destroy the enzymes necessary for proper flavor and color development, limiting its ability to ripen effectively later.
Salvaging Unripe Green Tomatoes
The largest portion of a frost-hit harvest often consists of green tomatoes, which can be divided into two groups: those mature enough to ripen and those that are not. Mature green tomatoes, often exhibiting a slight pale-green or “whitish” hue, contain sufficient reserves to complete the ripening process off the vine. These fruits can be placed in a cool, dark environment, ideally between 55 and 70 degrees Fahrenheit, to encourage a slow color change.
Ripening Mature Green Tomatoes
To hasten the process, mature green tomatoes can be stored with a high-ethylene gas producer, such as a ripe banana or apple, inside a paper bag or a box covered with newspaper. The ethylene gas released by the ripe fruit triggers the ripening enzymes, causing them to turn red over the next few weeks. Check these stored tomatoes every few days and remove any that develop soft spots or show signs of decay to prevent spoilage from spreading.
Using Immature Green Tomatoes
Truly unripe, hard green tomatoes that show no signs of turning color will not ripen successfully but can still be used for cooking. These are typically prepared in recipes like fried green tomatoes, relish, or pickles, where their firm texture and tart flavor are desired. Unripe tomatoes contain higher levels of the glycoalkaloid tomatine. Cooking and processing the fruit, such as in pickling brine, helps to ensure the safety of this late-season harvest.
Processing Slightly Damaged Ripe Tomatoes
Ripe or nearly-ripe tomatoes exposed to frost will likely suffer from compromised texture, making them unsuitable for fresh slicing. The freezing and thawing process causes the cell walls to break, resulting in a mushy, watery fruit. The first step is to carefully cut away any dark, soft, or bruised areas, salvaging only the firm, undamaged flesh.
These slightly compromised tomatoes are best utilized in cooked preparations where the texture does not matter and the excess water can be reduced. Making tomato sauce, paste, or soup base is an excellent way to use this fruit, as cooking concentrates the flavor and evaporates the surplus liquid. Dehydrating or drying the trimmed tomato pieces is another effective preservation method that concentrates their flavor.
For preservation methods like canning, the safety protocol is more stringent because frost damage can potentially raise the fruit’s pH level, reducing its natural acidity. If the vine was killed by the frost, the tomatoes are often considered unsafe for traditional water-bath canning methods unless additional acid, such as lemon juice or citric acid, is added and the fruit is fully sound after trimming. Freezing the cooked product is often the safest and simplest method for long-term storage.
Identifying and Discarding Unsafe Tomatoes
It is necessary to discard any tomatoes that pose a food safety risk or are beyond practical culinary use. Any tomato that froze solid and became completely mushy upon thawing should be immediately composted, as the texture and flavor will be unpalatable. The extensive cell damage in these tomatoes also makes them prone to rapid spoilage from bacteria.
Tomatoes showing signs of mold, rot, or fermentation must also be thrown out. Mold on soft fruits like tomatoes can penetrate deeply beyond the visible surface. Look for fuzzy patches of mold, a sour or off-putting odor, or any sign of leakage or significant internal breakdown. When in doubt about the condition or safety of a frost-damaged tomato, the most prudent course of action is to discard it.