1. Hotter Than Boiling
Clostridium botulinum is a very tough microbe, able to survive boiling temperatures and thrive in oxygen-free environments, where it multiplies and releases its deadly toxin. Home canners must use a pressure canner to achieve a temperature of 240 degrees F, which is only possible using 10 pounds of pressure in a pressure canner. Check the dial gauge for accuracy annually to ensure you're getting the pressure you need to obtain the correct temperature.
2. Quality Jars and Lids
You must use jars and lids in good condition if you wish to can vegetables properly to prevent botulism. Check the jars for chips or cracks that may prevent a perfect seal on the finished product. The bands you use to secure the flat lids should be free of corrosion. The sealing compound used in the flat lids is sufficient for one processing. You can only use the flat metal lids one time, and you must discard them after opening the stored vegetable.
3. Add Acid
The acidity of vegetables plays an important role in allowing or disallowing the growth of botulinum spores. With the exception of pickles and tomatoes, vegetables are low acid foods, which permit botulinum spores to grow. Foods with a pH of 4.6 or lower are less likely to serve as a host for botulinum spores. Look for canning recipes that include lemon juice, vinegar or ascorbic acid. Ascorbic acid is the scientific name for vitamin C, so you'll get a nutrient boost from this addition as well.
4. Leave Some Space
Exuberant canners may want to pack all they can into their jars, filling every available inch with their homegrown green beans. Although it seems efficient, filling the jars to the very top increases the chance of ruining the seal and subsequent spoilage of the vegetables. You must leave 1/4- 1/2 inch of headroom at the top of the jar to accommodate the expansion of the vegetables that occurs during processing.
5. Listen for the Ping
After you've processed your canned vegetables in the pressure canner, allow the jars to cool gradually. Don't rush the process by submerging the jars in cool water, or they may shatter. As the jars cool, you may hear the sealing process as the flat lids snap into place or make a pinging sound. If you aren't sure whether your jars have sealed, depress the flat lid with your finger. It shouldn't spring back. Don't attempt to help the seal by over-tightening the metal bands. This can actually break what was a successful seal.
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