Quart canning jars are containers, usually made of tempered glass, which are used for preserving foods by the process known as “canning”.  This process heats the canning jars and the food placed inside them under pressure to destroy as many mold spores and bacteria as possible while preserving the nutrients inside the food.  This process extends the shelf life, or the amount of time before the food becomes inedible due to spoilage, of the foods inside the quart canning jars.

On the internet, quart canning jars are sold in cases of 12 jars, plus the rings and the caps needed to cover the jars for about $22.00 USD.  They are sold in both the wide mouth and the regular mouth varieties.  The mouth size is the size of the opening through which the food is introduced to the jar.

Quart canning jars are not the only type of canning jars available.  There are also pint sized canning jars, half-gallon sized canning jars, gallon sized canning jars, and two gallon sized canning jars.  The latter sizes of canning jars are usually used by institutions such as universities and hospitals unless of course you have a large number of people in your family.

My parents canned all their own food, but considered even the quart jars to be too expensive to buy.  Instead, they re-used the jars found on supermarket shelves.  This is a dangerous practice as the jars found on supermarket shelves are not made to withstand the pressures reached in the cooker while the food is being processed and so are more likely to shatter or break apart while being processed or immediately after being removed from the pressure cooker.  This would happen quite often to my mother while she was processing the food, and as a child I learned to handle the canning jars she used gingerly until they were cool to prevent such breakage.

When a quart canning jar broke inside the pressure cooker, the cooker would need to be emptied, and all the jars inside would need to be minutely examined for damage. Undamaged jars would be placed on a shelf to cool, while the damaged quart canning jars, along with their contents, would be put in the garbage.  The interior of the pressure cooker would then be cleaned thoroughly before being refilled water and more canning jars and being replaced on the stove.