Alexandria gazette. [volume] (Alexandria, D.C.) 1834-1974, 1921-09-05
Temperature At Center of
Can Important In Canning

In canning work one of the most
important considerations is the time
required for the food at the center of
the container to reach the tempera-
ture of the retort of water bath in
which it is being ococessed. United
States Department of Agriculture
Bulletin $50 a Study of the Factors
Affecting Temperature Changes in
the Container During the Canning of
Fruitss1nd Vegetables, which has just
been issued, centers attention on these
time temperature relations. The pur-
pose has been to bring out the under
lying principles, rather than to lay
down definite rules of procedure. The
results of this experimentation are
of interest to scientific workers in the
field, to commercial canneries, and
similar large scale handlers of foods.
Successful preservation of foods by
canning is due primarily to the fact
that in the processing, or cooking, the
bacteria and other :nicroor garrisons
which cause spoilage are destroyed.
Since the elimination of these mic
roorganisms is dependent upon the
use of heat as a sterilizing agent, it
becomes of paramount Importance to
know just what temperatures and pro-
cessing periods will destroy them. If
uniformly good results are to be eX-
pected a sufficient degree of heat
must penetrate to all parts of the can
or jar and must be maintained long
enough to render all heterogeneous
harmless. Before an accurate judg
ment as to the proper cooking period
can be found it is necessary to know
how long time is required for the
heat to reach the food at the center
of the container.
The mercury thermometer, if prop
erly elaborated and standardized, has
been found sufficiently accurate for
practical work. A satisfactory appara-
tus has been devised for using the
mercury thermometer to measure
temperature changes at the center of
the can.
The fruits and vegetables as process
sed in these tests fall roughly into two
groups with reference to time-tem-
perarure at the enter of the can in
consists of those fruits and veget-
ables, such as string beans, packed so
that there is free liquid filling the
interspaces between the pieces of ma
terial. The rate of change of tenn
perature at the center of tn can in
this group is very rapid. The second
group consists of materials of heavy
or pastry nature that are packed in
such way that little or no convection
can occur, as with corn or sweet po-
tatoes. The rate Of change of tempe
nature in this group is very slow.
Sometimes mechanical agitation is
employed. Variations in the compost
ton of the material, however. have
very little effect if the consistency of
the material is such that no convec-
ton can occur.
Salt has very little direct effect
upon the rate of change of tempera
ture in the can. Dilute sugar solu-
tons have only small effect, but
the concentrated solutions retard the
rate of change. Solutions of starch
also retard it. In 5 per cent starch
the consistency becomes such that all
convection is stopped and the rate
change is very slow. Other material
Of q viscous nature, such as protein
or pectin, retards the rate of change
Of temperature. The retarding effect
Of glass container is of more import
ance in the first group than in the
second. Glass cools faster than tin
in the air, but can not be cooled in
water.
Differences in the diameter of the
container as only of Importance in
processing of materials Of heavy con-
sistency such as corn. Whether the
processing temperature is 100 degrees,