64 BULLETIN 956, U. S. DEPAKTMEISTT OF AGKICULTTJEE. 



(7) Differences in the diameter of the container are of much less 

 importance in those materials in which there is a free liquid than in 

 materials of heavy consistency. Thus there need be little difference 

 in the processing period of No. 2 and No. 3 tin cans of string beans, 

 but there must be considerable difference in the processing period 

 of No. 2 and No. 3 tin cans of sweet corn. 



(8) The temperature of the bath or retort is reached in the 

 container in approximately the same time, whether the processing 

 temperature is 100°, 109°, 116°, or 121° C. Tomatoes are a striking 

 exception to this rule, because the higher temperatures break down 

 the tissues of the fruit. 



(9) The difference in the rate of cooling in the air and water is 

 very marked. In materials having a free liquid the cooling is 

 exceedingly rapid, as in string beans, but is considerably slower in 

 materials having a heavy consistency, as in sweet potatoes. Cooling 

 in air is always very much slower than cooling in water. 



(10) Since a steam-tight closure in glass containers can not be 

 made, any temperature above 100° falls to 100° as rapidly as the 

 temperature of the retort, so that the temperature is always 100° 

 or below when removed from the retort. 



(11) In the intermittent process, the first processing period may 

 or may not affect the rate of temperature change in the second 

 processing period, depending upon the composition and nature of 

 the material. Any change during the first processing period which 

 interferes with convection retards the rate of change of temperature 

 during the second processing period. This change may be the 

 simple compacting of the material, the going into solution of starch, 

 protein, pectin, or any other mucilaginous material. If the material 

 at the outset is such that no convection occurs, then the gelatinization 

 of starch or other such change has very little effect upon the rate 

 of change of temperature in the can. 



(12) The fruits and vegetables as processed in these tests fall 

 roughly into two groups, with reference to time-temperature rela- 

 tions. The first group consists of those fruits and vegetables packed 

 so that there is a free liquid filling the interspaces between the 

 pieces of material. The rate of change of temperature in this 

 group is very rapid. The second group consists of those materials 

 that are packed in such a way that little or no convection can occur. 

 The rate of change of temperature in this group is very slow. 



