TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 35 



calculate corresponding curves for the different initial temperatures. 

 A series of curves calculated by means of this formula, using one of 

 the above experimental curves, will be found to agree closely with 

 the other experimental curves starting at different initial tempera- 

 tures. The formula is valuable in calculating curves of this sort in 

 that it saves much time and labor. 



Figure 21 also shows experimental curves for cooling both in air 

 and in water. Attention is directed to the very slow rate of cooling 

 in air as compared with that of cooling in water. The form of the 

 curves for cans cooled in water are of special interest. In the case 

 where the proportion of corn to liquor is the same as in the heating 

 curve (that is, 4 to 1) the temperature falls very rapidly at first, 

 but later the form of the curve becomes more regular and eventually 

 coincides with the second curve. 



In the corn of heavy consistency the lag at the beginning is greater, 

 and the temperature falls more slowly. If the head space in the corn 



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70 ( 



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 Tl 



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 ME IN 



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MINUT 



IZO 130 140 150 160 170 160 IK 



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Fig. 22. — Experimental time-temperature curves for " Maine style " corn in No. 2 tin 

 cans, starting at a uniform temperature of 80° C. ; processed for different time periods 

 at 116° C. ; and cooled in air at ordinary room temperature. Proportion of corn to 

 liquor, 4 : 1. The arrows indicate when cans wer.e removed from the retort. Curve 

 for can processed: A, For 30 .minutes ; B, for 45 minutes; G, for' 60 minutes; D, for 

 90 minutes. 



of heavy consistency is increased, the cooling will be faster and the 

 curve will resemble closely that for the can of corn having a normal 

 consistency. At temperatures above 100° C. and where the head 

 space permits there seems to occur a condensation of steam in the 

 head space, resulting in a simple sort of distillation which quickly 

 reduces the temperature below the boiling point of water. The re- 

 duction of the pressure in the head space causes ebullition and a con- 

 sequent stirring of the material, resulting in a rapid fall of tem- 

 perature. 



These results emphasize again the fact that cooling curves for 

 food materials are practically never the exact reverse of the heating 

 curves, even when temperatures of the surrounding medium are re- 

 versed. 



Figure 22 shows experimental curves for No. 2 cans of corn sealed 

 at 80° C. and processed at 116° for 30, 45, 60, and 90 minutes and 

 then cooled in the air at 20° to 25° C. 



