K-State Research and Extension

When preserving any food, use the best food possible for the safest results. This includes tomatoes. During the fall, many gardeners still have tomatoes on the vines. But once a frost or freeze happens, these tomatoes are not safe to preserve by canning.

When tomatoes are left on the vine towards the end of the growing season, the pH increases above 4.6. This is the dividing point whether a food is a high acid or low acid food. When the pH is above 4.6, it is a low acid food. These tomatoes are also more susceptible to other microbial damage. Tomatoes that have signs of blight or other fungus related infestations have a higher pH making them a low acid food. All of these are not safe for canning.

For information on preserving tomatoes, see www.bookstore.ksre.ksu.edu/pubs/MF1185.PDF.

Yes! That extra time is important and time well spent for safely canned tomatoes. This is true for any produce that is canned. For example, potatoes, peaches, and apples are also peeled before canning.

According to the National Center for Home Food Preservation, “Most bacteria, yeasts, and molds are difficult to remove from food surfaces. Washing fresh food reduces their numbers only slightly. Peeling root crops, underground stem crops, and tomatoes reduces their numbers greatly. Blanching also helps, but the vital controls are the method of canning and making sure the recommended research-based process times found in the USDA’s Complete Guide to Home Canning are used.”

Easily peel tomatoes by dipping them in boiling water for 30-60 seconds or just until the skins split. Then dip in ice water, slip off the skins and remove cores. See how at https://youtu.be/diZGx8RZAd0. This method can be used for peaches or nectarines.

As fall approaches, those end of season unripe tomatoes are still usable. Be sure to pick them before a frost or freeze if canning them.

Unripe, or green, tomatoes can be preserved just like ripe tomatoes. So when canning them they still require acidification. Here are some ideas to can green tomatoes.

• Pickled Green Tomato Relish
• Pickled Sweet Green Tomatoes
• Piccalilli
• Fall Garden Relish
• Rummage Relish
• Oscar Relish
• Green Tomato Pie Filling
• Tomatillo Green Salsa—may use green tomatoes instead of tomatillos
• Spiced Green Tomatoes

Don’t want to can them, or it is after a frost or freeze? Then freeze them for later use.

It is always best to preserve any food at its peak ripeness and freshness. Tomatoes that are overripe can be a problem if canned.

The acidity level in tomatoes varies during the growing season. If overripe, they are less acidic than when at the peak of ripeness.

Do not use damaged tomatoes or any that have mold growth. These may contain harmful pathogens that may not be destroyed during the canning process.

The best preservation method for these tomatoes is to freeze them.

Source: https://extension.umn.edu/preserving-and-preparing/canning-tomato-products-safety-guidelines

Treat all varieties and colors of tomatoes the same. They all require added acid for safely canned tomatoes. Learn more at www.bookstore.ksre.ksu.edu/pubs/MF1185.PDF.

The safety of canning tomatoes primarily rests on the pH, or acidity, of the tomatoes themselves. Some myths state that older tomato varieties, or heirloom varieties, are more acidic than todays modern tomatoes. But research has shown that this is not true.

Research conducted at three universities, North Dakota State University, University of Illinois, and Utah State University, show that many varieties of heirloom tomatoes are actually less acidic than todays tomatoes. To be considered a high acid food, the pH needs to be below 4.6. Many are above that pH level and into the 5.0 or above pH range.

This is why, no matter what variety of tomato you preserve, it is important to add acid in the form of citric acid, bottled lemon juice or vinegar to can them safely. See instructions at www.bookstore.ksre.ksu.edu/pubs/MF1185.PDF.

Sources: North Dakota State University Extension; Utah State University; and University of Illinois