The Bridgeport times and evening farmer., 1921-09-02
TEMPERATURE AT GAN CENTER
 IMPORTANT

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 or water bath in which is is being proceSSed. United States Department of Agriculture Bull detin 456, A Study of the Factors Af- fect1ng Temperature Changes in the Container During the Canning of Fruits and Vegetables, which has just been issued, centers attention on these time-temperature relations. The pur- pose has been to bring out the under lynis 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 microorganisms which cause spoiIage are destroyed. Since the elimination of these micro organisms is dependent upon the use of heat as a steriIizing agent, it be- comes of paramount importance to know just what temperatures and processing periods will destroy them. If uniformly good results are to be expected a. sufficient degree of heat must penetrate to all parts of the can or jar and must be maintained long enough to render all microrgantSnS harmless Before an accurate judg- ment as to the proper cooking period can be found 1t is necessary to know how long a. time is required for the heat to reach the food at the center of the container.
 The mercury thermometer, if prop erly caIibrated and standardized, has been found sufficiently accurate for practical work. A satisfactory appar- atus has been devised for using the mercury thermometer to measure temperature changes at the center or the can.
 The fruits and vegetables as pro- cessed in these tests fall roughly into two groups with reference to time temperature relations. The first group consists of those fruits and vegetables, such as string beans, packed so that there is a free liquid filing the inter spaces between the pieces of material. The rate of change of temperature at the center of the can is very, rapid The second group consists of mater ials of a. heavy or pastry nature that are packed in such a way that nttle or no convection can occur, as with corn or sweet potatoes The rate or change of temperature in this group is very slow Sometimes mechanical agitation is employed Variations in the composition of the material now ever, have very little effect if the consistency of the material is such that no conviction can occur
 Salt has very little direct effect up on the rate of change Of tempera!ure in the can. Dilute sugar solutions have only a small effect, but the con centrate dsolutions retard the rate Of change. Solutions of starch also re- tard it. In per cent Starch the con- sistency becomes such that all convec- ton is stopped and the rate of change is very slow. Other material Of a viscious nature, such as protein or pectin, retards the rate of change of ten1perature The retarding effect of a 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 are only of importance in the processing Of materials of heavy consistency such as corn Whether the processing temperature is 100,