Don't Use Low Acid Vinegar for Canning Food, Experts Warn

The recent popularity of low-acid vinegar products has food safety experts reminding people to use vinegar with 5% acidity when canning to avoid food spoilage and food-related illness.

Statistics suggest that around 71 million households in the United States have a garden. And about 18 million of those households only recently began growing their own food. So, it appears that gardening at home has become a new personalized farm-to-table experience for many.

But as the dog days of summer arrive, some people with gardens are facing mountains of produce ready to be canned or frozen. While both preservation methods deliver delicious results, canning can have some caveats, as it requires stricter adherence to proper processing and handling procedures to prevent food spoilage during storage.

Tomatoes, in particular, have been the subject of debate in the food preservation world because new varieties may have lower acidity than those grown by past generations. This lower acidity might impart a pleasant taste, but it's not helpful in the canning process, where a high acid content is necessary to ensure the canned tomatoes stay safe to eat.

The National Center for Home Food Preservation says adding lemon juice or 5% acidity vinegar to whole, crushed, or juiced tomatoes when canning is required to increase the acidity — even when pressure canning.

This is because the bacteria that causes botulism poisoning can grow in sealed jars at room temperature if the food's pH is above 4.6. While testing found that some current tomato varieties have pH values at or above 4.6, a few have a pH of 5 or higher.

In addition to canned tomatoes, even some salsa recipes and pickled vegetables need the added acidity of vinegar to ensure they are safe to eat later.

However, not all vinegar products are created equal, and some of the newly popular low-acid vinegar options may contain less than 5% acidity — which could make preserved food unsafe to eat.

According to Virginia Tech experts, distilled, white, apple cider, balsamic, red wine, malt, etc., contain acetic acid, and the percentage of acid in the product should appear on the label.

In a July 28 news release, Melissa Wright, director of the Food Producer Technical Assistance Network at Virginia Tech, says, "Some labels may also bear the concentration in grains, where 10 grain is equal to 1 percent acidity, so you'd want to look for 50-grain vinegar."

Wright warns, "Vinegars with less than 5 percent acetic acid concentration should never be used in home food preservation, as they can lead to unsafe pH levels and spoilage.

In addition, whether processing a simple tomato sauce or creating a signature salsa, Wright says that if a person is unsure about canning recipes or procedures, they should contact a local university extension agent. They can also consult the National Center for Home Food Preservation or the USDA's Complete Guide to Home Canning.