Research is continually being conducted in the area of home canning. As a result, recommendations may change. Many factors over which we have no control may cause seal failure or spoilage. Seal failure or spoilage may not be apparent from the appearance or odour of home-canned products. Consumption of spoiled food can lead to serious illness or death. ATCO Blue Flame Kitchen assumes no responsibility or liability for any seal failure or spoilage that may occur as a result of following the general information set out below.
Current preserving and food safety information recommend that all home-canned foods be processed. Processing means that jars are filled, leaving the correct headspace, and then heated in a boiling water bath or pressure canner for a specific length of time. This is done to destroy microorganisms and enzymes that may cause spoilage. This heating step also forces air out of the jars. As the jars cool, an airtight vacuum seal forms preventing air and microorganisms from re-entering the jars. Specific processing times are established through laboratory testing.
Whether you're new or experienced, questions on home canning come up. We have compiled some of the common questions we have received over the years.
High Acid Foods
High acid foods are food with a pH lower than 4.6. Most fruits are naturally acidic and can be made into jams, jellies, syrups and butters. Acid can also be added to some less acidic foods, such as carrots, tomatoes and cumbers to make relishes, chutneys and pickles. High acid foods are processed in a boiling water bath. For specific canning information, visit these pages:
Low Acid Foods
Low acid foods are foods with a pH of 4.6 or higher. Examples of low acid foods are:
- Meat, game, poultry, fish and seafood
- Soups and stews
- Tomato-vegetable mixtures without added acid (pasta sauce, vegetable juices, stewed tomatoes)
All low acid foods must be processed in a pressure canner. Temperatures of at least 240°F (116°C) are required to eliminate the risk of botulism and the only way to achieve this temperature is in a pressure canner. Visit our Canning Vegetables and Meat for more information.
Unsafe or Outdated Procedures
It is essential to replace outdated preserving procedures with updated ones. Avoid following the home canning advice of untrained celebrities, old cookbooks, back-to-nature publications and out-of-date home canning leaflets. Some of these unsafe or outdated procedures include:
- Sterilizing jars in the oven or dishwasher
- Open kettle canning (hot fill)
- Steam canning
- Microwave oven canning
- Oven canning
- Slow cooker and sun canning
- Turning jars upside down to cool after processing
- Sealing jam or jelly with paraffin wax
- Retightening screw bands of metal lids after processing
- Canning of tomatoes without added acid
- Water bath canning of vegetables, soup, meat, fish or poultry
Preparing the Jars and Lids
Glass canning jars must be sterilized before use. To sterilize jars, place upright into the rack in a boiling water canner or on a rack in a large pot. Cover jars with room temperature water. Cover canner with lid. Place over high heat and bring to a boil; boil rapidly for 15 minutes at elevations of 1001 - 3000 feet (305 - 914 meters) and 20 minutes at elevations of 3001 - 6000 feet (915 - 1829 meters). Leave water-filled jars in canner until ready to fill with prepared ingredients.
The flat piece of two-part metal canning lids must be prepared according to manufacturer’s instructions; leave in hot water until ready to use. If you do not have instructions for preparing these flat lids, place them into a small saucepan, cover with water and bring to a simmer. Do not boil as this can lead to seal failures. Screw bands do not need to be sterilized; keep at room temperature.
General Canning Steps
1. Before beginning, review the following information and assemble all equipment and ingredients.
2. Visually inspect canning jars for nicks, cracks, uneven rims or sharp edges that may prevent sealing or cause jars to break. Screw bands may be reused. Check to ensure screw bands show no rust, are in good condition and fit properly on jars. Discard any jars and screw bands that are not in good condition. Use new metal flat lids each time to ensure a vacuum seal. Wash jars, screw bands and lids in hot soapy water. Rinse well.
3. Sterilize jars just before use following PREPARING THE JARS AND LIDS, above.
4. Prepare ingredients according to recipe directions.
5. Drain one jar at a time into the sink and fill immediately with prepared ingredients.
6. Remove air bubbles by sliding a non-metallic utensil, such as a narrow rubber spatula or plastic knife, between the jar and ingredients. After removing air bubbles, add additional liquid, if required, to maintain directed headspace. Wipe jar rim thoroughly with a clean damp cloth.
7. Center flat lid on jar. Apply screw band just until “fingertip tight”. Do not overtighten. “Fingertip tight” allows some give between the lid and jar and allows air to escape during processing. This creates a vacuum seal as the product cools.
8. Place the filled jar into the raised canner rack. Repeat process with remaining jars. When all jars are filled or the canner is full, lower rack into hot water. Be sure jars are covered by at least 1 inch (2.5 cm) of water; add boiling water, if required. Place lid on the canner and turn heat to high.
9. When water returns to a full rolling boil, begin counting processing time. Reduce heat to maintain a gentle and steady boil for the required time. Turn off heat and remove canner lid. Allow boil to subside, then lift jars without tilting and place them upright on a rack, dry towel or a cutting board to cool in a draft-free place. Do not retighten screw bands or turn jars upside down as seals may be broken. Allow jars to cool undisturbed for 24 hours.
10. After cooling, check jars for vacuum seal by pressing on the center of each lid. Sealed lids curve downward and do not move. Refrigerate any unsealed jars and use them within one week or freeze or reprocess within 24 hours. Reprocessing is not recommended as it may give a significantly overcooked product. If a sealed jar becomes unsealed after some time in storage, this indicates spoilage from microbial growth. Discard the contents of the jar.
11. To store sealed jars, wipe with a clean damp cloth. Remove, wash and dry screw bands. Store separately or replace loosely on jars, as desired. Label jars and store in a cool dark place. As a guideline, use home canned foods within one year.
- Canning at High Altitudes
Note: ATCO Blue Flame Kitchen information and recommendations contained in this publication have been researched and are in accordance with current guidelines published by Bernardin Ltd. and the Cooperative Extension Service, University of Georgia. We acknowledge their assistance. The Bernardin Ltd. "Guide to Home Preserving" is available at retail outlets in Alberta.
The methods and procedures outlined in this publication are recognized as safe. Many factors over which we have no control may cause spoilage. ATCO Blue Flame Kitchen assumes no responsibility for any failures or spoilage that may occur.