Home canning tomatoes offers a rewarding way to preserve the flavor of summer, but the success of the final product depends heavily on the initial choice of fruit. Not every tomato variety is equally suited for the heat and duration of the preservation process. Selecting the right tomato impacts everything from the texture and consistency of the sauce to the safety of the sealed jar. Finding a good canning tomato involves understanding specific physical and chemical requirements that ensure both quality and safety for long-term storage.
Essential Physical Characteristics for Canning
The ideal tomato for canning possesses a high ratio of solid flesh, or meatiness, compared to its watery seed gel. This characteristic, often referred to as high solids content, is paramount for creating a thick, rich sauce or paste without hours of reduction time. Varieties with low moisture content yield more preserved product per pound of raw fruit, making the canning process significantly more efficient.
The physical structure of the tomato also determines its suitability for different preservation methods. For whole or diced canning, a tomato needs a thick, durable skin that resists collapsing during the heating process. This thicker skin helps the fruit maintain its shape and prevents it from turning into mush inside the jar.
A thick skin is advantageous because it allows for easier removal. When tomatoes are briefly blanched in boiling water, a thick skin separates cleanly from the flesh, simplifying the peeling process. Furthermore, a small locule, or seed cavity, is desired, as fewer seeds and less gel contribute to a denser, more desirable texture in the finished product.
Ensuring Safety: The Critical Role of Tomato Acidity
The most important factor in home canning is the acidity level, measured by pH. Tomatoes are a borderline acid food, with a natural pH that ranges from 4.3 to 4.9. For safe water bath canning, the food’s pH must be 4.6 or lower to prevent the growth of Clostridium botulinum.
The acidity of a tomato can fluctuate significantly based on factors like the variety, the stage of ripeness, and the weather during the growing season. Overripe tomatoes, for instance, tend to have a lower acid content than those picked at peak ripeness. This inherent variability means that no tomato can be relied upon to be acidic enough on its own.
The United States Department of Agriculture (USDA) recommends adding acid to all home-canned tomato products. This is done by incorporating a measured amount of bottled lemon juice or citric acid directly into each jar before processing. For a quart jar, this means adding two tablespoons of bottled lemon juice or one-half teaspoon of crystalline citric acid.
Bottled lemon juice is preferred over fresh-squeezed juice because its acidity level is standardized and consistent. This addition of acid ensures the pH falls below the 4.6 safety threshold, allowing for safe preservation using the boiling water bath method. Without this step, the product would require a pressure canner to reach temperatures high enough to destroy botulism spores.
Recommended Tomato Varieties for Preservation
The best canning tomatoes are “paste tomatoes” because their physical characteristics align with the requirements for thick sauces. Varieties like Roma, San Marzano, and Amish Paste are oblong and dense, offering the low moisture and high solids content necessary for a quick-cooking sauce. San Marzano tomatoes are prized for their minimal seeds and intense flavor, making them a frequent choice for premium sauces and pastes.
For canners who prefer a more general-purpose tomato, certain slicing or beefsteak types are suitable, though they will yield a thinner product. Varieties such as Rutgers and Celebrity are sturdy and flavorful, making them excellent choices for canning as whole tomatoes or for making juice. While they contain more water and seeds than paste tomatoes, their robust flavor holds up well to heat processing.
Heirloom varieties, like Black Krim or Brandywine, produce great flavor but are more unpredictable in terms of acid levels. Their high variability and moisture content mean they require the addition of acid and may result in a thinner, more rustic sauce. When choosing any variety, selecting determinate varieties that ripen all at once is efficient for large-batch canning.