636 STATE BOARD OF AGRICULTURE. 



Eva M. Briiett (7) used the well-known equation of monomolecnlar 

 reactions in investigating the shock effect of the blanching followed by 

 cold dipping upon the spores of B. 'pscudo-tetanicus. This is expressed: 



1 B 



k = — log — 

 t b 



in which k = velocity coefficient of the rate of death of bacteria, a con- 

 stant, 

 t = interval of time between observations, 

 B = nund)er of bacteria at beginning of any time interval, 

 b = number of bacteria at end of time t. 



She concludes from the data obtained that "The bacteriological utility 

 of the blanching in the cold pack process of canning probably should 

 not be ascribed to shock" as bacterial spores are apparently not made 

 more sensitive to heat by preliminary heating followed by chilling; 

 rather, what little justification blanching has from the bacteriological 

 standpoint should be ascribed to its initial cleansing action, and as the 

 time required for sterilization probably varies directly in proportion to 

 the initial contamination it is desirable to reduce this as much as possi- 

 ble. The suggestion is made that the blanching process may so influence 

 the hydrogen ion concentration of the liquid that the time needed for 

 sterilization would be markedlj^ influenced. 



Carrie E. Castle (10) in experimenting Avith intermittent heating (1 

 hr. on 3 successive days) says that in the hot water bath method, the 

 jars should not only be completely immersed in the water but the water 

 should be cold when they are introduced and only brought to the boiling 

 point afterwards. Loosely packed jars only should be used in canning 

 by usual home metliods. With shallow water baths the maximum in- 

 terior temperatures were considerably lower than in the deeper baths and 

 the higher temperatures in the latter cases were maintained for longer 

 periods. 



Bovie and Bronfenbrenner (0) describe an apparatus employing 

 thermo-couples for measuring the rate of heat penetration in tin cans 

 of navy beans. The graph given at the close of their article shows that 

 although a constant autoclave temperature of 280 degrees F. was reached 

 in 15 minutes, the interior of the can did not approximate this tempera- 

 ture for much more than 15 minutes during the last of the 180 minute 

 processing period. 



Thompson (27) by using thermo-couples embedded in the center of 

 cans of various foods, asparagus, carrots, chard, cherries, corn, peas, 

 strawberries, spinach, string beans, and squash, determined the tempera- 

 ture-time curves when the cans were subjected to various temperatures 

 in hot water, steam, cool air and cool water. From his experiences a 

 chart of time-temperature relations has been constructed which may be 

 used for determining approximate]}' the temperature at the center of a 

 can at any time after immersion in tlie processing bath which is main- 

 tained at a constant temperature. A chart of this kind devised for 

 variable bath temperatures would be of the greatest use in solving the 

 bacteriological problems of food canning. 



