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11.1.8 What about zinc rings, rubber sealed jars, and other antique (Out-dated or superceded are other terms) canning equipment?




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This article is from the Food Preserving FAQ, by Eric Decker ericnospam@getcomputing.com with numerous contributions by others.

11.1.8 What about zinc rings, rubber sealed jars, and other antique (Out-dated or superceded are other terms) canning equipment?

Lots of things are legal for sale but are not conducive to good health. Do not
confuse commercial availability and/or commercial use with suitability for
home-canning.

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 seal.

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 for canning.

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.

[N.B: In addition to being beautiful, some of those colored glass canning
jars are valuable collectors' items. Why bother canning with them?--LEB
[Food in blue jars? No thank you. Colour is a key indicator of food
condition. No canner will deprive herself of that advantage. -ED

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.
[N.B: Zinc lids are an especially bad idea for processing pickles, since
zinc is highly reactive in high salt and acid.--LEB

Mayonnaise jars or "one-trip" commercial jars are considered by some canners

[ they make excellent feed stock in recycling for manufacture of REAL canning
jars - ED ]

to be an inexpensive alternative to buying canning jars. ( use only for DRY or
highly acidic foods - pH proven to be lower than 4.0 )

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. This occurs 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.

As noted, the glass geometry is different than the standard canning jar. Canning
lids and rings will not fit well and most certainly will not attain the seal
they are desinged for. The seals of mayo-type jars are single use ONLY. It is
a false economy to use mayo-type jars for any form of preserving.

Prepared by Mary Keith, June, 1991
Revised by M. Susan Brewer, June, 1992
Revised by Eric Decker, January 2001

 

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