Michigan State University Extension
Preserving Food Safely - 01600738
10/13/97

### JAR BREAKAGE IN HOME CANNING

        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

             minutes.

            -Avoid  the  use  of  metal  tools  to  remove  air

             bubbles.

            -Avoid  using  very  old jars.   Jars have  a  life

             expectancy of about 10 years.

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