Selecting the correct variety of tomato is paramount for achieving a high-quality finished product when preserving the summer harvest. The best results in terms of flavor, texture, and yield depend heavily on the fruit’s inherent characteristics. Choosing the right tomato prevents a watery sauce, ensures whole tomatoes remain intact, and maximizes the usable pulp. Focusing on specific cultivars designed for preservation saves significant time during processing.
Defining the Ideal Canning Tomato
The qualities that make a tomato perfect for fresh eating are often the opposite of what is desired for canning. An ideal preserving tomato possesses a high ratio of solids to liquid, meaning it contains less water and gel surrounding the seeds. This characteristic is often referred to as being “meaty” and is a primary factor in reducing the cook-down time necessary to achieve a thick sauce or paste.
The texture of the canned product is heavily influenced by the tomato’s thick cell walls and high pectin content. Pectin, a natural polysaccharide, acts as a gelling agent, preventing the finished sauce or juice from separating into layers of water and pulp during storage. Tomatoes with thick walls and small seed cavities, such as paste varieties, naturally concentrate this pectin and flesh. Conversely, a slicing tomato with many seed chambers and high moisture content requires substantially longer cooking times to evaporate excess water.
The skin of a canning tomato is also typically thicker, which makes the process of blanching and peeling them much easier. Varieties that hold their shape well after being subjected to heat are preferred for whole or diced applications. Choosing disease-free, vine-ripened fruit is important, as damaged or overripe tomatoes can have a lower acidity level that affects safety protocols.
Best Varieties for Sauce, Paste, and Whole Canning
Paste tomatoes are the preferred choice for thick products like sauces, pastes, and ketchup because of their dense flesh and low seed count. The classic example is the San Marzano, an heirloom variety known for its sweet flavor, meaty texture, and two chambers. Its dense pulp cooks down quickly into a rich sauce with minimal effort.
Roma tomatoes are widely available and serve as an excellent, versatile option for both sauce and whole canning. As a determinate plant, the Roma often yields a large harvest all at once, which is convenient for large batch canning. Another highly-regarded paste type is the Amish Paste, a large, meaty heirloom that provides a rich, complex flavor to sauces.
For canning tomatoes whole or in large diced pieces, firm and thick-walled varieties are ideal to maintain structure through heat processing. While paste tomatoes like Roma and San Marzano are excellent for this purpose, certain slicer types can also be used if the excess juice is removed. Varieties like the Rutgers or Ace 55 are known for their firmness and ability to hold their shape well when canned whole.
Acidity and Processing Safety
Regardless of the variety chosen, every home-canned tomato product must be acidified to ensure safety from the deadly toxin produced by Clostridium botulinum. This bacterium thrives in low-acid, oxygen-free environments, exactly what a sealed jar of low-acid food provides. The threshold for high-acid food is a pH of 4.6 or below, but modern tomatoes, even those that taste tart, often hover near or above this line.
The safety protocol requires adding a measured amount of acid to every jar before filling with tomatoes. This is necessary because the acidity of tomatoes can fluctuate unpredictably based on ripeness, growing conditions, and variety. The recommended method is to add two tablespoons of bottled lemon juice or half a teaspoon of food-grade citric acid per quart jar.
Bottled lemon juice is specified because its acidity level is standardized, unlike freshly squeezed juice. Once acidified, the product can be safely processed using a boiling water canner, which destroys molds and yeasts. Although pressure canning is an option, acidification remains mandatory for all tested tomato recipes to guarantee the safe pH level.