Michigan State University Extension
Preserving Food Safely - 01600630


Crystals throughout jelly or jam may be caused by:          

-Too much sugar in the jelly mixture.                       

-Cooking the mixture too long or too slowly.  (Long slow    
  cooking results in too much evaporation of water).        

-Cooking  the  mixture too  little.   (When  sucrose  is    
  boiled in acid fruit juice to make jelly,  some of it     
  is "inverted", or broken down, to dextrose (glucose)      
  and levulose (fructose).  Sugar would probably            
  crystallize from most jellies if it weren't partially     
  inverted during the cooking process.  Too little          
  cooking results in insufficient sucrose inversion.        
  This  is  rarely  a problem in jellies  made  without     
  pectin since they require fairly long cooking.  How-      
  ever,  sugar  may  crystallize from jelly  made  with     
  added pectin because the boiling time-one  minute- is     
  too short to bring about much inversion.                  

     Crystals  that form at the top of jelly that  has  been
opened  and  allowed to stand are caused by  evaporation  of

     Needle-like  crystals  in grape jelly may  be  tartaric
acid,  the  natural substance in grapes from which cream  of
tartar  is made.   To prevent formation of tartrate crystals
in  the  jelly,  let extracted grape juice stand in  a  cool
place  (refrigerator)  overnight,  then strain  through  two
thicknesses of damp cheesecloth to remove crystals.         

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