Date: May 1989 (Revised April 1995)
Source: University of Minnesota
Time, energy and money are lost when food spoils. There are several reasons home-canned foods spoil. The most common ones are: failure to heat process the filled jars, processing by an incorrect method, processing for insufficient time, and failure of lids to seal.
When you can low-acid vegetables and meat, you must use a pressure canner. Because the pressure canner keeps steam confined until it builds up pressure, it can build up temperatures above the boiling point. You need these high temperatures to destroy botulism spores that can cause food poisoning in low-acid foods. At 10 pounds pressure at sea level used in home pressure canning, you will get a temperature of 240 degrees F. Adjustments need to be made as altitude increases. You must maintain the recommended pounds of pressure throughout the processing period. If at any time during processing the pressure drops, the food will not be adequately processed. Whenever pressure drops below the recommended processing level, bring it back up and re-time for the entire period needed for the particular food.
In many old canning books, there are no instructions for heat processing jars of food after filling. The older books describe a canning method called "open-kettle canning", and spoilage with this method is quite common. Because the filled jars are not pasteurized or sterilized by heating after the lids are put on, molds, yeasts and bacteria survive and can cause food to spoil. The lids may seal at first, but later on become unsealed, indicating that food is spoiling. Do not use this method for any home-canned food.
When foods canned in a pressure canner spoil, it is usually due to one of the following reasons:
If you used a boiling water bath canner and canned food spoils, the cause could be failure to have water hot when you placed the jars in the canner, not having enough water to cover the tops of the jars by at least an inch, processing for too short a time, or processing low-acid foods with this method.
If you have further questions, contact your county office of the NDSU Extension Service.
Back to Canning Menu
Go to Ask Extension Index Page
For More Information Contact your North Dakota County Extension Office of the NDSU Extension Service for additional information or see our main NDSU Web Page for publications and articles on Agriculture, Horticulture, Youth and Family, Business and Community and Food and Nutrition at http://www.ag.ndsu.nodak.edu/