When most people think of home canning foods they often think of canning tomatoes or homemade salsa. A national survey in 2005 indicated that 59% of home-canners added tomatoes to their pantry shelves in one season alone. As we approach August here in Michigan, fellow canners will begin stocking up on this kitchen staple.
When home canning this year, keep in mind not all tomatoes are created equal. There are thousands of varieties throughout the world and giving Michigan’s climate and soil, not every tomato has the same acidic value. In home canning, achieving the proper acidic value will make or break the preservation process.
Tomatoes for many years were considered high in acid, however, tomatoes are fruits and, as such, the amount of acid in tomatoes varies dramatically over the growing season. The amount of acid in tomatoes is highest in unripe (green) fruit and attains a lower acidic value as the fruit reaches maturity.
To successfully home can tomatoes, the fruit must have an acidic value of 4.6pH or lower allowing home canners to water bath their recipe. Anything with a low acidic value (a pH of 4.7 or higher) the recipe must be pressure canned to properly kill bacteria. Even though these two preservation methods are available to home canners, I am often asked, “Well how can you tell if a tomato is high in acid?”
Valid question, tough answer. Many seed catalogs use descriptions such as a tomato being “low acid”. Sadly, all this means to the reader is the fruit will have a sweeter taste over other more acidic-tasting tomatoes. The description means nothing to the fruits pH level. More confused? Don’t be.
Researchers now know tomatoes are not consistently high enough in acid alone and current canning recommendations require acid be added to all canned tomato products. Acid can be added to each jar in the form of bottled lemon juice, citric acid or vinegar containing a minimum 5% acidic value.
Many factors play a role in determining a recipes acidic value. When home canning, do not think in terms of each ingredient separately, but rather the recipe as a whole. Take for instance, my Basil Diced Tomato. Although the main ingredient is Roma tomatoes known for being higher in acid, I add other vegetables and fresh herbs which lower the overall acidic value of the entire recipe. Because of this, I play it safe by adding lemon juice to the recipe which naturally increases the acidic content and pressure can the jars instead of water bathing. Another example of this is home canning Stewed Tomatoes.
My best advice is to follow a tried and true recipe with ingredients and processes which uphold safe home canning practices. And even though every tomato is different, rest assured knowing no matter which tomato you choose, there are ways keep your home canned foods safe and delicious all year long!
So this August, whether you are picking your own tomatoes off the vine or stopping in at your local farmers market, enjoy preserving Michigan’s beautiful bounty safely and in a variety of delicious ways!
Fun Fact: Botanically, the tomato is a fruit. It is classified as such because the portion that is eaten contains reproductive structures (seeds). But in 1893, the tomato was declared a vegetable by the United States Supreme Court. The reason involved the collection of import duties. So, the tomato is either a fruit or a vegetable, depending on whose definition is used.
–Diane Devereaux, The Canning Diva