by Magda D. Healey

Created on: January 11, 2010

Preparation of the jars is crucial to successful and safe home canning of produce.

Canning, or bottling is a time-honored way of preserving food well known to our grandmothers well before the advent of freezing. It's healthier than salting or pickling, preserves most nutrients and more universally applicable than drying.

Canning relies on application of heat (effectively, pasteurization) to kill the harmful bacteria and other organisms that would lead to spoiling of food. The jars are usually sealed by creating a vacuum inside that further prevents spoilage. The products most commonly canned at home are now fruits and vegetables, although meat can also be successfully canned (this is more hazardous and has a danger of producing a botulism toxin which develops in low-oxygen conditions).

The jars used for home canning vary by country, but the most common jars now used are Mason or Kilner jars with a twist-off metal lid and an elastic seal. Glass preserving jars with rubber sealing rings can also be used for canning.

Whichever type of jar is being used, the most important par of preparation is through washing of the jars: use hot water and washing up liquid, or simply place the jars in the dishwasher. If hand washing, rinse the suds (the British habit of not rinsing dishes should be avoided in this case as nobody likes a subtle flavoring of Fairy washing up liquid in their fruit) and then dry the jars on either using a clean, fresh tea towel or air dry on a rack.

Dry (or damp, but not dripping with water) jars should be then sterilized. How necessary this step is largely depends on the product being canned - anything with high sugar content or very acidic will be naturally preserved, but produce canned au naturel will need pretty sterile environment not to spoil, and particularly, not to develop mold. The easiest way to sterilize jars is to put them into a low oven (about 100-120C) for at least 10 minutes. Jars washed on a hot cycle in a dishwasher can be considered to be already sterilized for most purposes.

If the produce is to be canned traditionally using heat (in a water bath oven or pressure cooker), the jars don't need to be sterilized, but should still be washed thoroughly.

While selecting the jars, make sure to check the edge for chips and discard any with uneven edge - a chip is not only a hazard but will prevent the seal taking place and let the air in.

Lids and rubber sealing rings (when used) should also be thoroughly washed in hot water. If using metal lids, discard any which are obviously rusty (especially for acidic fruit) or deformed. If using glass lids, discard any with chips. If using rubber sealing rings, discard any that are deformed or show signs of slackness.

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