Fresh foods
contain air which can cause loss of color and nutritional value when
canned. Raw-packed foods tend to float in the jars, while hot packing
allows more food to be placed in each jar. Immediately after canning,
the color of hot-packed foods may not appear any better than raw-packed.
However, within a short storage period both color and flavor of
hot-packed foods will be superior. Hot-packed foods have a better vacuum
seal and longer shelf life.
Directions for hot packing specific foods are available in University of
Missouri canning publications, the Ball Blue Book, University of
Georgia’s So Easy to Preserve and the National Center for Home
Food Preservation website mentioned in the accompanying article.
Proper headspace another canning quality factor.
Headspace is the unfilled space above food in a canning jar and below
the lid. This space is needed for expansion of food as jars are
processed and for forming the vacuum in cooled jars. A high jar vacuum
is important for an airtight seal and for maintaining good color, flavor
and nutritional value.
How much food expands during processing depends on the air content of
the food and the processing temperature. Temperatures are higher in
pressure canning than boiling water canning, so headspace recommendation
vary with the type of canning method. Generally, jams and jellies need
¼-inch headspace, acid foods processed in boiling water need ½-inch
headspace, and low-acid foods canned in a pressure canner need 1- to 1
¼-inch headspace.
Other May 2005
Articles:
Home Food Preservation Appeal
to do-it-Yourselfers
Canning and Freezing for One, Two or a Few
Strawberry Rhubarb Jelly
May 2005
