Selecting Canning Jars and Lids



If you are going to invest the time, the produce, your own energy
and your electrical energy in home canning, then it should be
important to you to select the best containers for your food. Here
are some pointers to guide you, or maybe to give you some answers
about why the jars you have used in the past broke in the canner or
did not sealed. 

The best jars to use are standard canning jars.  There are several
brands on the market.  They are all suitable. However, as in any
mass-produced product, you may find a few mistakes.  Be sure to
check the rims, or sealing surfaces. Run your fingertip lightly
around the circle to check for any chips or bumps. These will
prevent the canning lid from sealing properly.  Also look to see
that the rim is circular. Occasionally a jar will stick momentarily
in the mold and an oval jar is the result. These curiosities can
not be used. 

While the jars themselves will last for decades, until they are
broken,  their safe life for canning is much shorter.  With the
repeated heating and cooling of canning, the glass gradually
becomes more brittle.  Eventually, it becomes very sensitive to
even light shocks.  Older jars are often the ones that break in the
canner for no obvious reason.  Glass manufacturers generally say
that a canning jar will have a reliable life of 12 to 13 years. 
After that their tendency to break increases, and they should be
replaced.  This includes most of the blue glass jars.

Many of the older jars were made for use with rubber rings and zinc
lids.  In this style of lid, the seal was not on the rim of the jar
mouth but on the shoulder, below the threads. Therefore, the
smoothness of the rim was not important.  Many of these jars have
rough rims, and rims of uneven thickness.  These jars will not seal
reliably with today's lids.  They can be used to store grains and
pasta, but are not a good choice for canning.

Mayonnaise jars or "one-trip" commercial jars are considered by
many canners to be the inexpensive alternative to buying canning
jars.  For some foods that is true.  Mayonnaise jars may be safely
used for canning foods in a boiling water bath canner.  They are
generally reliable and will not break at that temperature. 
However, they should never be used in a pressure canner.  The glass
sides are slightly thinner than in a standard canning jar.  When
there is a pressure difference between the inside of the jar and
its environment they may explode.  Thisoccurs when the canner cools
while the contents of the jar are often still boiling.  In
addition, the rims of mayonnaise jars are often thinner than those
of canning jars.   This means that there is less space for the jar
lid to properly seal onto.  It is very important that the lid be
carefully adjusted onto the jar and be exactly centered. Otherwise
it may not seal.



Prepared by Mary Keith, June, 1991
Revised by M. Susan Brewer, June, 1992