30 



BULLETIN 956, U. S. DEPARTMENT OF AGRICULTUEE. 



These curves indicate that the lieat penetrates into the cans very 

 slowly. It requires two hours to approach the temperature of the 

 retort in a No. 2 tin can and nearly three hours to reach the same 

 temperature in the No. 3 can. In one and one-half hours the pint 

 glass jar approaches the temperature of the retort and in about two 

 hours the same temperature is reached in the quart glass jar. It is 

 very evident, therefore, that little convection is taking place. Con- 

 vection is prevented in part by the finely divided condition of the 

 corn, and further by the viscous condition of the liquor, which 

 results from gelatinization of the starch. The differences in the rate 

 of change of temperature between the No. 2 and No. 3 tin cans are 

 very great, indicating the necessity of different processing periods. 



no 



70 



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20 JO 'fo SO eo 



Fig. 32. — Time-temperature relations for sweet corn (Maine style) when processed in 

 No. 3 tin cans at 100°, 109°, 116°, and 121° C. These curves were plotted from read- 

 ings made at intervals of 5 minutes. Rise in temperature when processed : A, At 

 100° C. ; B, at 109° C. ; C, at 116° C. ; D, at 121° C. 



The difficulty of getting the heat to the center of a No. 3 can and the 

 quart glass jars is so great that it is advantageous to can sweet corn 

 in No. 2 tin cans or in pint glass jars. It is to be noted that the 

 low conductivity of the glass ceases to be a factor here, and the rate 

 of change of temperature follows more nearly the order of the 

 diameters of the containers, i. e., the pint glass jar is fastest, then the 

 No. 2 tin can, the quart jar next, and the No. 3 can slowest. This 

 order is quite different from that of string beans. 



Stirring the material would very greatly aid in getting the heat 

 to the center of the can for corn prepared in the Maine style, and for 

 this reason agitating cookers might be especially advantageous for 

 handling corn packed in this manner. 



