It's bad enough when a filled canning jar breaks in the canner,
making a mess and ruining a jar of good food. But when it happens more than once
in a great while, that indicates a problem we can correct! What causes a canning
jar to break is not quite the mystery that it appears to be.
Breakage can occur for many reasons. Here's my
Top 10 List (apologies to David Letterman) of Why Canning
Using lower quality commercial food jars
rather than jars manufactured for home canning Miracle Whip and
mayonnaise jars are the perfect size and the threads fit, but they break
so easily in the canner they just aren't worth. Some spaghetti sauce jars
(those whose tops fit a standard canning lid and ring) do seem to be more
robust, and I don't recall ever having a "Classico brand spaghetti sauce jar
Using jars that have hairline cracks Admittedly, hairline
cracks can be difficult to see and few of us carefully inspect every jar for a
thin crack before using them.
The lids were overtightened As the contents of the jar heat
and expand, the air in the headspace is pushed out of a tiny gap between the lid
and the jar, while the ring keeps the lid from lifting up too much and allowing
water in! It works like a one-way valve, letting the expanding air out.
This is necessary to create the vacuum, when you remove the jars from the
canner, the contents cool, contract and suck the lids down. So, don't make the
lids as tight as you can; just snug. Follow the lid manufacturer's
Putting hot food in cold jars I leave my jars in the
dishwasher on "heated dry", after running the "sanitize cycle". Some
people fill their jars with the hottest water from their facet until the are
ready to fill them. And of course, sterilizing them by submersing the
empty jars in the canner or in a large pot of boiling water works well. If
a jar is going to break, it would most likely do it then, while it is still
Putting cold food in cold jars and then immersing into the
canner Food and jars should be hot when placed in the canner. Sudden change in temperature create too wide a margin between temperature of
filled jars and water in canner before processing. That leads to "thermal
shock" in the glass jar.
Food was packed too solidly or jars were overfilled. Then as
the jars heat in the canner, their contents expand and the jar breaks! Follow
the recommendations for headspace, which are specific to each type of food.
Some expand more than others, too!
Putting jars directly on bottom of canner instead of on a rack.
This is easy to correct! Use a rack! I like the better quality stainless
steel racks best, but in a pinch a wash cloth on the bottom of the canner
(inside, of course) will work.
Pressure canners have their own specific issues causing jar breakage:
- Canner became dry during the processing period. This is caused by either a
steam leakage in your canner, which means you need a new part, or by using
insufficient water for the processing period. - Jars were placed directly on
canner bottom. A canning rack should always be placed on the canner bottom. It
is not necessary to place a rack between a layer of pint or half-pint jars.
Stagger the jars by placing a top jar on two bottom jars. - Pressure was
reduced quickly after processing. Always let pressure drop of its own accord.
- Air was exhausted from canner at too high a temperature. Adjust heat so a
steady gentle flow of steam emerges from the vent pipe. - Pressure had
fluctuated during the processing period. This can be caused by an unsteady heat
source or steam leaking from the canner.
Jars were placed in a cold, drafty place to cool. Always
allow the jars to cool jars on a towel or rack at room temperature, away from
windows, vents and drafts.
And finally, the jars themselves may be the cause of difficulty.
Jars eventually weaken with age and repeated use. Repeated
heating and cooling cycles take a toll.
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Cleaning supplies to remove rust from rings and jars
A visitor wrote in to tell how she uses Copper Glo (order at ledt) to
remove rust from rings and jars:
Comments from a visitor on September 15, 2010: "You mention not using
jars that have rust on them. One way to remove rust from jars is with Copper
Glo. I get Copper Glo at our local Giant Eagle. I had a jar with rust on it
and was getting ready to pitch it when my mom told me about Copper Glo. I
was afraid to use it at first because I was afraid it would scratch the jar,
but decided it was worth a try. Amazingly, the rust came off and the jar
Rubber seals for the older zinc caps - Know first thathome
canning experts do not recommend that you use the rubber ring system. The
modern flat lid and metal ring system (above) is superior in reliability and
safety. If you insist in using the rubber ring system, do not use old rubber
rings: they have aged and will probably not seal effectively, especially on
an older jar. You can get new rubber canning rings quite inexpensively
Canning & Preserving for Dummies by Karen Ward
Average Customer Review:
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The All New Ball Book Of Canning And Preserving: Over 350 of the Best Canned, Jammed, Pickled, and Preserved Recipes Paperback - May 31, 2016
This is THE book on canning! My grandmother used this book when I
was a child. It tells you in simple instructions how to can almost
anything; complete with recipes for jam, jellies, pickles, sauces, canning
vegetables, meats, etc. If it can be canned, this book likely tells
you how! Click on the link below for more information and / or to buy (no
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Complete Guide to Home
Canning and Preserving
by United States Dept. of
guide contains virtually everything consumers need to know about home
canning: how to select, prepare, and can fruits, vegetables, poultry, red
meats and seafoods; how to preserve fruit spreads, fermented foods and
pickled vegetables; how to prepare foods for special diets, and much more.
Also includes scores of simply written recipes that even beginners can
handle (smoked fish, turkey-tamale pie, chicken croquettes, more. It's the
second book to get, after the Ball Guide.
Click on the link at left for more information and / or
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