Reasons why Home Canning Spoils (2007)

When home-canned food spoils, it is a waste of your time, energy and money. Why do home-canned foods spoil? The most common reasons include failure to heat-process the filled jars, processing for insufficient time, and failure of lids to seal.

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 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 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 you can low-acid vegetables and meat, you must use a pressure canner. Because this utensil 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 the 11 pounds of pressure used in home pressure canning, you will get a temperature of 240 degrees F.

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 retime for the entire period needed for the particular food.

When foods canned in a pressure canner spoil, it is usually due to one of the following reasons:

- An inaccurate dial gauge.

- Failure to vent steam from the canner for ten minutes before closing the petcock or placing the weighted pressure control on the canner. This allows air to remain in the canner, and temperatures will be lower than needed.

- Fluctuating heat under the canner.

- Processing for too short a time.

If you used a boiling water bath canner and the canned food spoils, it was caused by:

- Not having enough water to cover the tops of the jars by at least an inch.

- Fluctuating heat under the canner or interrupting the boiling process.

- Processing for too short of a time.

- Processing low-acid foods with this method.

Discard any canned food you suspect may be spoiled. For more information contact your local cooperative extension office.

For more information on this subject, Please visit the College of Agricultural Sciences Publications Web site.

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