Canning Food Properly Is Vital

Food preservation season has arrived.  Please do it correctly so you don’t invite botulism to your dinner table.

Botulism is a deadly form of food poisoning. It’s most commonly associated with improperly processed home-canned vegetables, such as peas, peppers, corn, lima beans, green beans and mushrooms, as well as other low-acid foods that are canned at home, including soups, meats, fish and poultry. However, it also can be associated with commercially canned foods, although rarely.

If canned food isn’t processed properly, spores of the bacteria Clostridium botulinum aren’t killed and may produce a deadly toxin (poison) in the food.

Just a teaspoon of pure botulism poison could kill millions of people, according to the national Centers for Disease Control and Prevention. Even just a taste of contaminated food can make a person sick or worse.

Botulism symptoms include blurred or double vision, slurred speech, difficulty swallowing, muscle weakness, nausea, vomiting, stomachache and diarrhea. The symptoms usually start to appear 18 to 36 hours after eating food containing the toxin. Botulism is treatable if the victim receives prompt medical care. Without treatment, the illness causes paralysis that starts with the head and moves to the arms and legs and can cause death, the CDC says.

We’re in the heart of home canning season, so it’s critical to use up-to-date equipment and research-tested methods. Be aware that home-canned tomatoes need to be acidified with lemon juice or citric acid and properly processed to be safe.

The proper equipment for safely canning low-acid foods such as vegetables and meat includes a pressure canner and standard canning jars with new two-piece lids. Do not use your oven or dishwasher to seal foods, even if you found a unique idea on Pinterest or Facebook. Those methods are not safe at all.

Foods such as salsa, which is a mix of acid and low-acid ingredients, need to be properly acidified with lemon juice or vinegar using a tested formula and processed according to current recommendations.  If you have a favorite salsa recipe that hasn’t been research-tested, it’s safest to freeze it rather than can it.

Food containing the botulism toxin generally doesn’t taste or look unusual, although the cans may provide a clue that the food is contaminated. Throw away any cans that are swollen or bulging and food from glass jars with bulging lids. You also shouldn’t taste food from swollen containers or food that is foamy or smells bad.

You also should get rid of recalled canned products without opening the cans. For information on the brand names and UPC codes of recalled foods, visit the FDA Web site at

To keep humans and animals away from the tainted food, the Food and Drug Administration advises double bagging it in plastic bags and disposing of it with nonrecylable trash.

But even properly processed commercially canned foods won’t last forever. For example, cans and metal lids on glass jars can rust. The acid in foods such as tomatoes and fruit juices can cause cans to corrode. Light may cause food in glass jars to change color and lose nutrients. Temperatures above 100 F can cause food to spoil.

Here is some advice for storing canned foods:

* Store them in a cool, clean, dry place where temperatures are below 85 degrees. Temperatures in the 60- to 70-degree range are ideal.

* Store commercially-canned low-acid foods (such as green beans and peas) in a cupboard for up to five years, but they should be used within a year for best quality.

* Use high-acid foods (such as tomato-based products) within 12 to 18 months. Foods stored longer will be safe to eat if they show no signs of spoilage and the cans don’t appear to be damaged, but the food’s color, flavor and nutritive value may have deteriorated.

* For research-based information on home canning, freezing, drying and pickling, visit the NDSU Extension Web site at and click on “Food Preservation.”


Julie Garden-Robinson, Ph.D., R.D., L.R.D., is a professor and food and nutrition specialist with the NDSU Extension Service.