Pasteurising food in jars, commonly called "canning", is a popular way to store food without refrigeration. Pasteurising is effective as a method of sterilising food because bacteria cannot survive when exposed to temperatures above 82.2 degrees Celsius for an extended period of time. Many foods including vegetables, picked products, jellies and meats can be safely stored by canning.
Determine if your food is high-acid or low-acid. High-acid foods can be canned using a hot water bath, whereas low-acid foods require a pressure canner. You can test the pH using litmus paper and increase the acidity by adding lemon juice. A low-pH indicates a high-acid food.
Determine the correct jar size and processing time based on the food you are canning, your kitchen's elevation and the method you are using - water bath or pressure canner - will factor into the overall processing time and jar size that you use. Refer to Home Canning Pressures and Processing Times (http://msuextension.org/publications/HomeHealthandFamily/MT198329HR.pdf)
Clean and sterilise your jars. In order to sterilise your jars, place them right side up in your boiler, cover with water and boil for at least 10 minutes. Simmer your lids in a separate pot.
Fill your boiler with water and insert the rack. Turn on the burner to begin preheating the water.
Fill the empty jars with food. Depending on what you are canning you will use a hot pack - filling jars with hot food - or a raw pack - filling jars with raw food, such as green beans, and boiling water.
Remove air bubbles from jars using a non-metallic spoon or spatula and stirring the contents of the jar. Top off the jars after all air bubbles have been removed.
Clean the mouth of the jar using a wet paper towel. Be sure that there is nothing on the mouth of the jar that will prevent the lid from sealing.
Apply the preheated lid and screw on the ring as recommended by the jar's manufacturer. A lid that is too loose may allow food to leak, whereas a lid that is too tight may lead to broken jars.
Place the jar into the boiler using a canning jar lifter. Repeat this process until your canning rack is full.
Process your jars for the recommended amount of time. High-acid foods in a hot water bath are heated to a rolling boil (100 degrees Celsius) before the time begins. Low-acid foods in a pressure canner are heated to between 116 and 121 degrees Celsius and 4.54 Kilogram pressure before processing time begins.
Remove jars from hot water bath immediately and let cool for 12 hours. Pressure canners should be allowed to cool and should not be opened until the pressure gauge has returned to zero.
In order for the pressure gauge to function properly, pressurised canners must be vented (by boiling for 10 minutes thus forcing all air to escape) prior to sealing.
Botulism is a rare food poisoning cased by the bacterium Clostridium botulinium and it can be fatal. Be sure to use the correct method and processing time for the food you are pasteurising.
Tips and warnings
- In order for the pressure gauge to function properly, pressurised canners must be vented (by boiling for 10 minutes thus forcing all air to escape) prior to sealing.
- Botulism is a rare food poisoning cased by the bacterium Clostridium botulinium and it can be fatal. Be sure to use the correct method and processing time for the food you are pasteurising.