Michigan State University Extension
Preserving Food Safely - 01600498
10/13/97

### LID SELECTION, PREPARATION, AND USE

        The  common self-sealing lid consists of a  flat  metal

    lid
     held in place by a metal screw band during  processing.

    The
     flat  lid is crimped around its bottom edge to  form  a

    trough,
     which  is filled with a  colored  gasket  compound.

    When
     jars are processed, the lid gasket softens  and  flows

    slightly
    to cover the jar-sealing surface, yet allows air to

    escape
    from the jar. The gasket then forms an airtight  seal

    as
     the jar cools.  Gaskets in unused lids work well for  at

    least
    5 years from date of manufacture.  The gasket compound

    in
    older unused lids may fail to seal on jars.

        Buy  only the quantity of lids you will use in a  year.

    To
     ensure a good seal, carefully follow the  manufacturer's

    directions
     in  preparing lids for use.  Examine  all  metal

    lids
     carefully.  Do not use old, dented, or deformed  lids,

    or
    lids with gaps or other defects in the sealing gasket.

        After  filling jars with food, release air  bubbles  by

    inserting
     a  flat plastic (not metal) spatula  between  the

    food
    and the jar.  Slowly turn the jar and move the  spatula

    up
     and  down to allow air bubbles to  escape.   Adjust  the

    headspace
    and then clean the jar rim (sealing surface)  with

    a
     dampened paper towel.  Place the lid, gasket  down,  onto

    the
     cleaned  jar-sealing  surface.   Uncleaned  jar-sealing

    surfaces
    may cause seal failures.

        Then  fit  the  metal screw band  over  the  flat  lid.

    Follow
    the manufacturer's guidelines enclosed with or on the

    box
    for tightening the jar lids properly.

        DO  NOT RETIGHTEN LIDS AFTER PROCESSING JARS.  As  jars

    cool,
     the contents in the jar contract, pulling  the  self-

    sealing
    lid firmly against the jar to form a high vacuum.

        *  If screw bands are too loose, liquid may escape

           from jars during processing, and seals may fail.

        *  If screw bands are too tight, air cannot vent

           during processing, and food will discolor

           during storage.  Overtightening also may cause

           lids to buckle and jars to break,  especially

           with raw-packed, pressure-processed food.

        Screw bands are not needed on stored jars.  They can be

    removed
    easily after jars are cooled.  When removed, washed,

    dried
      and  stored in a dry area, screw bands may  be  used

    many
     times.  If left on stored jars, they become  difficult

    to
    remove, often rust and may not work properly again.

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