Michigan State University Extension
Preserving Food Safely - 01600630
10/13/97

### CRYSTALS IN JELLY

    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

    water.

        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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