NDSU Extension - Mercer County


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Preserving Summer’s Bounty

food preservation, canning, food processing

Submitted by Dena Kemmet, Extension Agent/Family and Community Wellness

I recently received a call from someone questioning the safety of processing times on an old recipe. I appreciate the reminder! With the resurgence in gardening, people are “putting up” canned goods again. Food preservation recommendations have changed through time as scientists learn what is and isn’t safe. Plus, vegetable varieties available today are not the same as those grown when your great-grandmother was canning. For example, tomato varieties have been bred to be less acidic to appeal to our modern tastes. An old recipe could have dire results when using current tomato varieties.

Botulism, one of the deadliest types of foodborne illness, is caused by eating improperly canned food. Commercial canners are extremely cautious about their canning procedures, but they have occasional safety recalls due to a botulism risk, too.

Vegetables are low-acid foods, meaning they do not contain enough acid naturally to prevent spores (forms of bacteria) from surviving and growing. Spores can produce a deadly toxin in an airtight environment, such as a sealed jar, unless the food is acidic or has been heated under pressure for a specified time.

Boiling food will not kill the spores. For safe canning of low-acid foods, a pressure canner must be used. Using a pressure canner allows the mixture to reach a higher temperature than a boiling water bath canner.

Unfortunately, foods containing the botulism toxin usually do not have an unusual taste or appearance. You cannot tell it is there. 

Improper canning can lead to the development of deadly bacteria and toxins. This is why using up-to-date equipment and research-tested methods when preserving food is vital.

When you preserve food at home, especially by canning, you are a scientist. Food preservation isn’t the time to put on your ‘creative’ hat.

Selecting the right container for preserving your garden’s bounty is just as important. Mason-type jars are the best choice for canning. Some people like to re-use glass mayonnaise or salad dressing jars. The National Center for Home Food Preservation says that is OK if new two-piece lids are used. However, they have a narrower sealing surface and are tempered less than Mason jars, so expect more seal failures and breakage when reusing jars that once held commercial products. Don’t process mayo jars in a pressure canner.

To seal jars, use self-sealing lids that consist of a flat lid and a screw band. Tighten the screw band with your fingers, not your muscles, because overtightening can lead to seal failures. You can reuse screw bands, but don’t reuse lids.

In addition to using research-tested recipes, be sure you have all the equipment and supplies you need. The Mercer County NDSU Extension office has a pressure gauge tester. Call before you bring the gauge if possible.

Visit the NDSU Extension office or website at https://www.ag.ndsu.edu/food/food-preservation for free information and some tasty, research-tested recipes.

Let us know if you would be interested in a hands-on food preservation class. If we have enough interest, we may schedule a class later this summer or early fall.

Source: Julie Garden-Robinson, Ph.D., R.D., L.R.D., NDSU Extension food and nutrition specialist

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