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.                     

Go To Top of File        MSU Extension Home Page        Main Page for this Data Base

This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This information becomes public property upon publication and may be printed verbatim with credit to MSU Extension. Reprinting cannot be used to endorse or advertise a commercial product or company. This file was generated from data base 01 on 03/09/98. Data base 01 was last revised on 10/13/97. For more information about this data base or its contents please contact wrublec@msue.msu.edu . Please read our disclaimer for important information about using our site.