How to Sterilize Canning Jars
The airtight vacuum seal of Ball, Kerr & Bernardin glass jars is designed to keep jam, marmalade, conserves, pickles relishes, chutneys, sauces & other preserves fresh.
Preserving food is becoming more popular, and knowing how to sterilize glass Mason jars is the first step in making great jams and pickles. More important, safe food handling helps prevent food poisoning.
Glass Mason jars are most commonly sold in the U.S. under the brand names Ball and Kerr, and in Canada under the brand name Bernardin. There are also more contemporary looking jars available from such companies as Weck.
A standard Mason jar comes with a flat metal lid with a red rubber strip around the bottom edge and a metal screw-on band that holds the lid on the jar while it is being processed in boiling water. Once the jar has been boiled, however, the vacuum seal is all that holds the lid on. A lid that is not tightly fixed to the jar is a good indication that the food inside has started to spoil.
Standard and Wide Mouth Mason Jars
Canning jars come in standard sizes with either a wide or a narrow mouth: half-pint (8 ounces), pint (16 ounces), quart (32 ounces), and half-gallon (64 ounces). This means that a thrifty cook can collect used jars. Replacement bands and lids can be bought separately. The bands can be reused, but the lids should only be used once and then discarded. The old-fashioned method of using a paraffin wax seal is no longer considered to be a safe one.
The method described in this article for hot water bath canning can be used with high-acid fruits and vegetables. A modern recipe should be used. Low-acid fruits and vegetables, fish, and meats cannot be safely preserved in a simple hot water canner; they require a pressure canner.
Supplies Needed for Sterilizing Mason Jars
- Canner (a large pot with a wire insert for sterilizing glass jars, available in many hardware stores, as well as chain stores like Walmart in the US or Zellers in Canada, and in kitchen supply stores.)
- Jar lifter (pictured)
- Basket strainer or equivalent
- Newspaper or dishtowel
- Jars, bands, and lids
How to Sterilize Canning Jars
- Wash jars in hot, soapy water.
- Set clean, empty jars (without lids) upright on a wire rack in canner. They should not be stacked upon one another, and they should not be crowded too tightly, so they do not break in the boiling water.
- Cover with water, making sure there are at least two inches of water over the top of the tallest jar.
- Bring to boil. This may take as much as 30 minutes. To speed it up, start the pot with water that’s hot from the faucet, and cover the canner while it is heating up. (This is a good time to start cooking the food to be preserved if there is adequate room on the stovetop.)
- When the water has reached a full rolling boil, start timing. Allow the jars to remain in the canner for a full ten minutes by the clock at a full rolling boil.
- The jars are now sterile. Place sufficient lids and bands into a basket strainer or some other container that will allow them to sit in the hot water. Put the lid back on the canner, turn off the heat, and prepare the food to be preserved.
How to Process Food in Jars
- When the food is ready, lift the jars carefully out of the hot water, pour the water out and fill them to within about ¼ inch of the top with hot food (check the recipe for the best head-room). Avoid touching the jar’s rim.
- Gently wipe any food spills off the rims and place a lid on each jar.
- Screw on the bands, but only fingertip-tight; hot air must be able to escape from the jars when they go back into the canner.
- Set the filled jars upright in the canner. Again, they should not be stacked, and they should not touch too closely. It is normal for them to release a lot of bubbles when they hit the water.
- Turn the heat up again. When it reaches the boiling point, start timing, and leave the jars in the canner for as long as the recipe calls for.
- Use the jar lifter to remove jars from the canner one at a time and place them on a heat-resistant surface on a layer of newspaper or a dishtowel in case of drips. Do not tilt them, and do not touch them or try to tighten the lids for at least 12 hours. Expect to hear a loud pop from each jar as the cooling process sucks the lid tight against the jar.
- Test the tops of the jars when they are cool, . If a top is loose or can be popped in and out, there is no seal. Refrigerate the jar and eat it right away.
- Label the jar with contents and date. Properly sealed jars will keep food fresh for anything from a few weeks to several years, depending on the contents.
The satisfaction of assembling a shelf of homemade preserves and the pop of a properly sealed lid being opened are just some of the rewards of learning how to sterilize canning jars properly.