Michigan State University Extension
Preserving Food Safely - 01600738


There are several types of breaks that occur. Each
break looks different and has specific causes. If the
reason for jar breakage can be determined, faulty procedures
can be corrected so this problem does not occur.

Thermal shock is characterized by a crack running
around the base of the lower part of the jar and sometimes
extending up the side. To prevent thermal breakage:

-Avoid sudden temperature changes, such as putting
a hot jar on a cool or wet surface or putting hot
food or liquid in a room-temperature jar. Keep jars
in hot water until filled.

-Use a rack in the canner.

-Avoid using metal knives or spatulas to remove air
bubbles or steelwool pads to clean jars. They may
damage the glass and make it susceptible to
thermal shock.

The internal pressure break is characterized by the
origin of the break on the side. It is in the form of a
vertical crack which divides and forks into two fissures.
To prevent pressure break:

-DO NOT USE the oven method for processing home-
canned food.

-Provide adequate headspace in jars for food to
expand when heated.

-Keep heat steady when processing.

-Avoid reducing canner pressure under running water
or lifting the pressure control or petcock when
pressure drops to zero at room temperature.

The impact break originates at the point of impact and
fissures radiate form the point of origin. To prevent
impact break:

-Handle jars carefully. Jars that have been
dropped, hit or bumped in transit or at home are
susceptible to breakage. Test new jars that may
have been mis-handled by immersing them in room-
temperature water, bring to a boil and boil 15

-Avoid the use of metal tools to remove air

-Avoid using very old jars. Jars have a life
expectancy of about 10 years.

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