As a member of the nightshade family, tomatillos (Physalis philadelphica) are closely related to tomatoes (Solanum lycopersicum). Tomatillos are annual plants and simple to grow. When growing tomatillo plants for their edible fruits, it is important to consider acidity because acidity determines the right soil for the plants, proper canning practices for the fruits as well as the nature of the fruits.
In the Soil
Growing conditions play a part in determining the health of tomatillo plants and their crop yield. It is important to provide tomatillo plants at least eight hours of full, direct sunlight daily as well as well-draining soil. Tomatillos are not heavy-feeding plants and are adaptable to soils of different fertility; however, the correct soil pH is important for the plants to thrive. Tomatillos grow best in slightly acidic soil, with a pH of 6.0 to 7.0. Use a home soil test kit to test your soil's pH.
As a Food
Foods are placed in two categories: acidic or alkaline. Certain foods, including some citrus fruits, are acidic. Tomatillo fruits, called tomatillos, belong on the list of highly alkalizing foods due to their effect on the body's pH level. When it comes to preserving tomatillos through canning or using them to make salsa, however, they are considered on the borderline between a low and highly acidic food and must undergo a process of acidification so they do not spoil.
Acidification for Preservation
Canning is a process used by many gardeners to preserve fresh fruit and vegetable crops beyond the growing season. Tomatillos are canned alone or with other ingredients to make salsa verde, also known as "green sauce" in Mexican cuisine. Tomatillos may be canned using a boiling water bath or a pressure canner. Typically, a pressure canner is used only for fruits of low acidity, but that canning process also is recommended as the best way to prevent spoilage in tomatillos. Lemon juice or citric acid are added to canned tomatillos and tomatillo-based salsas because their acidity prevents spoilage.
During the canning process, acidic ingredients are added to canning jars before tomatillos are added. About 2 pounds of tomatillos make 1 quart of fresh canned fruits. When making salsa, 5 cups of tomatillos with their husks removed make roughly 2 pints of salsa. The acidity of these fruits is increased by the addition of 2 tablespoons of lemon juice or 1/2 teaspoon of citric acid to each 1-quart-size jar. When using 1-pint jars, add 1 tablespoon of lemon juice or 1/4 teaspoon of citric acid. Vinegar is also an appropriate ingredient to increase acidity during canning, but it has the potential to change the flavor of salsa or fresh tomatillos.