- Food and Cooking
Home Canning Safety
Modern Home Canning
Water Bath versus Pressure Canner: What’s the big deal?
Some foods are high in acid (a pH of 4.6 or lower) and others are not. So what does it matter? The acid content of the higher acid foods has enough acidity to prevent the growth of bacteria and other micro-organisms that cause dangerous food spoilage and also destroy them rapidly when heated. So what foods are high in acid?
- All fruits except figs
- Most tomatoes
- Fermented vegetables
- Jams, jellies and preserves
For these foods a Boiling Water Processing at 212° F is sufficient. Processing times vary by the type of food, the size of the jars, and density of the contents and can range from 5 to 85 minutes. Always refer to your tested recipe for the proper processing time.
Figs and tomatoes require some extra care. Bottled lemon juice, citric acid or 5% vinegar must be added to acidify them to the proper pH so they can be safely processed in the Boiling Water Canner.
Low acid foods (pH 4.6 or greater) need to be sterilized at 240° to 250° F from 20 to 100 minutes to kill the bacteria and control all risks of botulism, a fatal toxin produced by the bacterium Clostridium botulinum. Boiling water cannot reach these temperatures. Low acid foods include:
- Mixtures of low and high acid foods
A pressure canner must be used for these foods. This canner builds up steam under pressure and can reach the higher temperatures when operating at 10 to 15 pounds of pressure per square inch (PSI). Exact processing time depends on the food, density and jar size so make sure you refer to your tested and approved recipes for proper processing times.
It is best to store canned foods between 50 and 70° F. NEVER, never, never eat food from a jar when the lid is popped or has become unsealed in storage. This is a clear sign of spoilage and often is botulism which can be fatal. Though one of the goals in canning is to remove the air, Clostridium botulinum is