Home canning is an excellent way to preserve garden produce and share it with family and friends, but it can be risky—or even deadly—if not done correctly and safely according to Iowa State University Extension and Outreach. Steer clear of the following canning mistakes.
Making Up Your Own Recipe: Use only up-to-date, scientifically tested recipes approved by the United States Department of Agriculture (USDA) and follow directions exactly. Good sources are the USDA Complete Guide to Home Canning, the National Center for Home Food Preservation, and land-grant university publications. Without scientific testing, there is no way to know how long the product needs to be processed to be safe.
Processing Low-Acid Foods in a Water Bath: Canning low-acid foods requires special care. This includes red meats, fish, poultry and all vegetables (except for acidified tomatoes). Low-acid foods can support the production of the deadly botulism toxin if these foods are not processed properly in a pressure canner. A pressure canner heats food to high temperatures (240-250 degrees F or higher) and destroys the spores that produce the botulism toxin. A boiling water bath canner, which can be used for canning pickles or fruit, heats food to boiling temperature (212 F), which is not high enough to ensure safety for canning vegetables and other low-acid foods.
Not Venting the Pressure Canner: Trapped air inside a pressure canner lowers the temperature obtained for a given pressure and results in under processing. To be safe, the USDA recommends that all pressure canners be vented 10 minutes before they are pressurized.
Rushing the Pressure Canner Cool-Down Time: The natural cool-down of the canner is part of the tested processing time. Hurrying this process will result in under-processed food and siphoning of liquid from the jars. It may also cause jar breakage.
Failure to Acidify Canned Tomatoes: Because the pH of tomatoes is an unknown, the USDA recommends that bottled lemon juice be used to lower the pH of the product to be unquestionably safe.
Canning by Electric Pressure Cooker, Oven, Open Kettle, Microwave, or Dishwasher: Boiling water bath or pressure are the only approved canning methods. Any other method should be avoided as foods will be under processed and unsafe. Heat is conducted by air in an oven which is less efficient than water or steam. As a result product temperature never exceeds the boiling point; jar breakage is also a possibility. Open-kettle canning, placing hot food in jars and sealing with no further heat treatment, has been considered an unsafe home canning practice since the 1980’s due to insufficient heat to destroy bacteria. Microwaved food reaches 212°F but heating is not uniform. The water temperature of the dishwasher’s cleaning and rinsing cycles is far below that required to kill harmful microorganisms. While electric pressure cookers use pressure for cooking, they do not meet the appliance standards for home pressure canning, even if marketed as safe for pressure canning.
Home canning is perfectly safe but needs to be done correctly. If you are new to canning (or need a refresher), see our Food Preservation page.
Article released August 30, 2021
