process of preserving food by heating and sealing it in airtight
containers. The process was invented (1809) by Nicolas Appert, a
French confectioner. In the Appert process, the food was cooked in
open kettles and placed in glass jars, which were sealed by corks
wired in place. The jars were then heated by submersion in boiling
water. Commercial canning was introduced into the United States in
1821 by the William Underwood Company of Boston.
Early Canning Methods
1810 an English inventor, Peter Durand, patented the idea of using
tin-plated cans. Later, calcium chloride was added to the water
used to sterilize the food sealed in the cans, to raise the
temperature of the water above 100° C (212° F). Although the
food was heated faster, the increased internal pressure often
burst the cans. In 1874 the closed-vessel process, in which the
cans were heated by steam under pressure, was invented; the
pressure of the steam compensated for pressure that developed in
the can, largely eliminating the bursting of cans.
improvements in machinery and techniques for producing cans
resulted in better lining materials, such as lacquers and enamels,
and in the development of the sanitary open-top can, in which the
top is crimped to the can after filling, producing an airtight
seal by means of a rubber gasket. Other developments include the
use of cans made of aluminum, very thin steel, and coated and
uncoated plastic. Can openers are unnecessary for cans that have a
pullable metal tab or ring attached at the top.
the widespread popularity of canned foods, the major limitation of
canning is in the quality of the final product. Since food is not
a good conductor of heat, excess heat needs to be applied to the
container's surface for a period of time to guarantee sufficient
heat at the center, or "cold spot," in order to destroy
all organisms causing spoilage and disease. This method of
preserving causes foods to lose juices, texture, flavor, and
nutrients. The retort pouch, developed in the 1970s to alleviate
this problem, is a 3-layered laminate with flexible plastic films
as the outer and inner layers and aluminium foil in the middle.
The pouch, which is approximately 19 mm (0.75 in) thick, is filled
and sealed under vacuum. Because the pouch has a large
surface-to-volume ratio, heat needs to penetrate less than 10 mm
(0.38 in) from the surface to the "cold spot," thereby
yielding greatly improved products.
is a process of preserving foods in vacuum-sealed cans or
3-layered flexible pouches with sterilizing doses of ionizing
radiation. The source of radiation may be gamma rays of cobalt-60
or cesium-137, X rays, or electrons. Because the food is
irradiated while frozen (-40° to -18° C or -40° to 0° F), the
limitations of conventional heat sterilization are not
encountered. As with frozen foods, radappertized foods, prior to
vacuum sealing and freezing, must be heated to 70° to 80° C (158°
to 176° F) to inactivate viruses and autolytic enzymes that cause
loss in texture and flavor. Use of this method on a commercial
scale awaits approvals by national health authorities.
canning became an important method of preserving food after the
American John Landis Mason invented (1858) a practical glass jar
and lid, now called the mason jar. The preferred method for home
canning is the hot-pack method, in which precooked, hot food and
part of the liquid in which it was cooked are placed in a clean,
hot mason jar. The mouth of the jar is covered with a metal disk
that has a rubber ring seal. A screw-type lid is then partially
screwed onto the glass jar. After the jar has been processed in
boiling water for the length of time required for the type of
food, the screw top is tightened completely. Heat and pressure
during processing force most of the air from the jar and minimize
the danger of multiplication of disease-causing organisms. Jams
and jellies are usually prepared by the open-kettle method. The
jam is cooked to the proper consistency, then poured into hot,
sterilized jars, which are then sealed. Further heating is not
required; the sugar used in preparing jams and jellies acts as a
Processing and Preservation.
Edward S. Josephson, Ph.D.
Adjunct Professor, Food Science & Nutrition Research Center,
University of Rhode Island.
an outline for this article.
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