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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