Are Tomatoes Acidic Enough for Canning?

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Are tomatoes acidic enough? The safety of your family depends on whether there is enough acid when canning. Find out how to be sure.

-by Patrice Lewis The decision whether to water-bath or pressure can food product comes down to one primary factor: Acid. How much natural acid is in a food determines the safest means by which it should be canned. In a nutshell, acidic foods are usually canned in a water bath, while low-acid foods are canned in a pressure canner. The bacterial spores that cause botulism are unable to produce toxins when in a high-acid environment.

The acidity of a food is determined by its pH, which has a scale from 1 to 14. Seven is considered neutral; anything below 7 is acidic, anything higher is alkaline. The lower the number, the stronger the acid. For both commercial and home canning, the point separating low-acid from high-acid foods is pH 4.6.

High-acid foods (which have a pH of 4.6 or lower on the pH scale), or some foods which have acidifiers added to them, are safe to water bath can. Combined with high temperatures, high-acid foods are hostile to “spoilers” during canning, which means they can be water-bath canned.

High-acid foods include all fruits, fermented foods such as sauerkraut, and properly acidified foods such as pickles and preserves.

Which tomatoes are acidic enough for safe canning?

Tomatoes are one of the most commonly canned garden products, but are tomatoes acidic enough? Most people think of tomatoes as a vegetable, but biologically speaking, they’re fruit. Historically, tomatoes were considered safe to water-bath can, and these canning procedures or tomatoes were often handed down from generation to generation. Unfortunately, these generational methods are no longer safe.

Why not? Consider some history. In the 1970s — at the height of the hippie back-to-the-land movement, when canning hit a huge resurgence— there arose some cases of botulism poisoning from home-canned tomatoes, which left people scratching their heads in confusion. Are tomatoes acidic? Why would tomatoes suddenly be unsafe to can in a water bath? The tomatoes in question had been processed according to proper procedures at the time. What happened?

Breeding is what happened. Modern tomato breeds, both open pollinate as well as hybrid, have been bred for ease of harvesting as well as milder flavor and are often lower in acid than their heirloom ancestors. Some current varieties have pH values as high as pH 5 or higher.

Using heirloom breeds is no guarantee of sufficient acidity. An heirloom variety simply means it breeds true, not necessarily that it’s an ancient line. A low-acid hybrid can become open-pollinated(“heirloom”) after only seven generations, or seven years, of breeding true.

What else causes low acid tomatoes?

There are other factors that can cause tomatoes to be low-acid. Bruises, cracks, blossom-end rot, insects, and over-ripening can reduce acidity levels. Tomatoes that are ripened off the vine, grow in areas with shortened daylight hours, or grow in the shade tend to have a lower pH than those ripened on the vine in full sunshine. Do not can tomatoes from dead or frost-killed vines.

For all these reasons, it’s important to add acidifiers to tomatoes, regardless of whether they’re heirloom or open-pollinated, since you never know if it’s a newer “heirloom” with a low-acid content. Botulism is NOT a risk to mess around with.

An acidifier will make tomatoes acidic.

What is an acidifier? Simply put, it’s an ingredient designed to lower the pH in a jar of food. The most common acidifiers are lemon juice, vinegar, and citric acid (available in many grocery stores, health-food stores, or online). If using lemon juice, use only commercially bottled lemon juice (fresh-squeezed lemon juice has variable and unknown acidity levels). If using white or cider vinegar, make sure it has 5%acidity (do NOT use homemade vinegar since the acidity level is unknown).

An acidifier must be added to crushed, juiced, or whole tomatoes prior to canning. It can be added directly to the jars before filling them with the product.

• If using lemon juice, add 2tablespoons/quart of tomatoes (or 1tablespoon/pint).
• If using citric acid, add ½teaspoon/quart of tomatoes (or ¼teaspoon/pint).
• If using vinegar, add 4tablespoons/quart (or 2tablespoons/pint). Keep in mind vinegar may change the flavor of the product.

Adding an acidifier is recommended even when canning produces high-acid tomatoes. It takes mere moments and ensures you won’t have to ask, “Are tomatoes acidic enough?” and your tomatoes will be safe.

Acidifying other tomato products.

Acidifiers are necessary to create a low enough acid environment to allow tomatoes to be safely water bath canned. However, even if pressure-canning tomatoes, the acidifier should be added.

If tomatoes are blended with low-acid foods such as meat, peppers, onions, etc., then they MUST be pressure-canned according to the ingredient requiring the most processing time. There is no exception to this. Are tomatoes acidic enough for pressure canning? No. Acidification is still necessary for pressure-canned tomato products such as salsa or spaghetti sauce. The amount of acidifier should never be reduced. If desired, sugar can be added to offset the tartness of the acid.

It’s crucial to use tested recipes, especially when it comes to tomato recipes such as salsa, spaghetti sauce, etc. A tested recipe is one in which every component and proportion has been laboratory tested, including measuring the temperature of a product inside the jar to make sure the food is sufficiently heated during the scanning process. Be careful of using recipes posted on social media sites or by celebrity chefs, since they aren’t necessarily using or sharing tested recipes.

It’s also important not to alter tested recipes. Ingredients can be subtracted or divided, but never added or multiplied (for example, a recipe’s quantity of onions can be halved, but never doubled).

Acidifying Tomatoes: Safe is Best

For canning anything —including tomatoes — an authoritative and up-to-date canning guide is essential. (Try the USDA’s Complete Guide to Home Canning which can be found at this link:https://www.nifa.usda.gov/aboutnifa/blogs/usdas-complete-guide-homecanning)

None of these warnings or cautions is meant to scare people away from the incredibly rewarding practice of canning. Acidifying tomatoes and using safe canning practices are a small and easy price to pay in exchange for the amazing world of food preservation that opens up — and that includes canning the remarkably flexible tomato.

PATRICE LEWIS is a wife, mother, homesteader, homeschooler, author, blogger, columnist, and speaker. An advocate of simple living and self-sufficiency, she has practiced and written about self-reliance and preparedness for almost 30 years. She is experienced in homestead animal husbandry and small-scale dairy production, food preservation and canning, country relocation, home-based businesses, homeschooling, personal money management, and food self-sufficiency.

Follow her website www.patricelewis.com/

or blog

www.rural-revolution.com/

Originally published in the September/October 2023 issue of Countryside and Small Stock Journal and regularly vetted for accuracy.