Michigan State University Extension
Preserving Food Safely - 01600501


     Many  fresh foods contain from 10 percent to more  than
30  percent air.  How long canned food retains high  quality
depends on how much air is removed from food before jars are

     Raw-packing  is  the practice of filling  jars  tightly
with  freshly  prepared,  but unheated  food.   Such  foods,
especially fruit, will float in the jars.  The entrapped air
in and around the food may cause discoloration within 2 to 3
months  of  storage.   Raw-packing  is  more  suitable   for
vegetables processed in a pressure canner.                  

     Hot-packing is the practice of heating freshly prepared
food  to boiling, simmering it 3 to 5 minutes, and  promptly
filling jars loosely with the boiled food.  Whether food has
been hot-packed or raw-packed, the juice, syrup, or water to
be  added  to  the foods should also be  heated  to  boiling
before adding it to the jars.  This practice helps to remove
air  from  food tissues, shrinks food, helps keep  the  food
from floating in the jars, increases vacuum in sealed  jars,
and improves shelf life.  Preshrinking food permits  filling
more food into each jar.                                    

     Hot-packing  is the best way to remove air and  is  the
preferred pack style for foods processed in a  boiling-water
canner.  At first, the color of hot-packed foods may  appear
no better than that of raw-packed foods, but within a  short
storage  period, both color and flavor of  hot-packed  foods
will be superior.                                           

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