Michigan State University Extension
Preserving Food Safely - 01600951
10/13/97

TESTING JAR SEALS

    After cooling jars for 12 to 24 hours, remove the screw

bands
and test seals with one of the following options:     

    Option 1.  Press the middle of the lid with a finger   


               or thumb.  If the lid springs up when you   


               release your finger, the lid is unsealed.   


    Option 2.  Tap the lid with the bottom of a teaspoon.  


               If it makes a dull sound, the lid is not    


               sealed.  If food is in contact with the     


               underside of the lid, it will also cause a  


               dull sound.  If the jar lid is sealed       


               correctly, it will make a ringing,          


               high-pitched sound.                         


    Option 3.  Hold the jar at eye level and look across   


               the lid.  The lid should be concave (curved 


               down slightly in the center).  If center of 


               the lid is either flat or bulging, it may   


               not be sealed.                              

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