Ensuring High-quality Canned Foods (2/2)

INGREDIENTS

INSTRUCTIONS

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 sealed.  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 2 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. Controlling Headspace  The unfilled space above the food in a
jar and below its lid is termed  headspace. Directions for canning
specify leaving 1/4-inch for jams  and jellies, 1/2-inch for fruits and
tomatoes to be processed in  boiling water and from 1- to 1-1/4-inches
in low- acid foods to be  processed in a pressure canner This space is
needed for expansion of  food as jars are processed, and for forming
vacuums in cooled jars.  The extent of expansion is determined by the
air content in the food  and by the processing temperature. Air expands
greatly when heated to  high temperatures; the higher the temperature,
the greater the  expansion. Foods expand less than air when heated.
======================================================= === * USDA
Agriculture Information Bulletin No. 539 (rev. 1994) * Meal-Master
format courtesy of Karen Mintzias  From Gemini's MASSIVE MealMaster
collection at www.synapse.com/~gemini

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