The incidence of people preserving food by canning in the oven or in the dishwasher is increasing as many gardeners and home cooks are looking for a shortcut to preserve their fresh produce at home. However, these are unsafe canning practices. Using unsafe canning practices can cause a deadly foodborne illness called botulism, which is virtually undetectable.
It is estimated that there are 55 actual cases of botulism annually in the United States. Although this is small in comparison to other foodborne illnesses, the death rate associated with foodborne botulism is as high as 17.3 percent. The cause for each case was inappropriate home canning methods, not recognizing the signs of food spoilage, and unawareness of the risk of botulism from home canned foods.
Signs of food spoilage in home canned products include:
- Bulging lids and unsealed jars
- Dried food starting at the top of the jar
- Rising air bubbles and unnatural color
- Unnatural odors
- Spurting liquid
- Cotton-like mold growth on top of the food surface and underneath the lid
Botulism causes a very deadly type of foodborne illness that begins usually within 72 hours after consuming the contaminated food. Symptoms can include digestive upset, blurred or double vision, difficulty swallowing or breathing, paralysis, and eventually death.
Canning in the oven and dishwasher does not heat the food in the jars to a temperature high enough to kill any and all pathogens that may be present in the food. It is important to remember that a sealed jar does not mean food inside the jar is safe to eat. It takes less heat to seal a jar than it takes to make the contents safe. Depending on the type of food, ALL canning must now be canned in a boiling water canner (high acid foods) or a pressure canner (low acid foods).
To ensure that your home canned goods are safe, be sure you are using recipes that follow the most current canning guidelines. Significant changes were made in 1994 that are critical to the safety of some processes. These included changes in canning tomatoes, pickles, and meat processing. Also, other recipes were reviewed and updated for safety and food quality. In 2006 and again in 2009, canning guidelines were reviewed and revised. For this reason, all recipes should be 1994 or later.
Some recommended resources include:
- ISU Extension and Outreach Food Preservation Resources
- Ball: Blue Book, Complete Book of Home Preserving (1994 or later)
- So Easy to Preserve
- USDA Complete Guide to Home Canning
- National Center for Home Food Preservation