54 PASTEURISATION OF MILK AND CREAM. , 


station. In a few preliminary observations on the condi- 
tions of efficient pasteurisation the authors state that two 
distinct rules have been formulated as necessary, viz. (1) 
the avoidance of a cooked taste or flavour in the treated pro- 
duct ; and (2) the destruction, as far as possible, of fermenta- 
tive.or disease bacteria. They point out that milk heated 
to a temperature of 160° F. or over acquires a more or less 
pronounced scalded flavour, varying in intensity with the 
period of heating, contact with the air, and other factors. 
“To destroy the different. bacteria requires a temperature 
that varies with the condition of the germ. Ifthe organisms 
are present in the resistant spore stage, no single application 
of heat will entirely destroy them, unless the exposure is made ~ 
for a number of hours. In the vegetating, growing condi- 
tion, which stage comprises about 95-99 per cent. of the 
organisms present, by far the larger majority are killed when 
inilk is heated to 135°-140° F. for 10-15 minutes. Even such 
disease forms as cholera, diphtheria, and typhoid fever 
germs cannot withstand the above temperature, while 
the sour milk species for the most part succumb readily 
under these conditions.” 
But while these conditions as to heat and time of 
exposure might be considered sufficient for ordinary pas- 
teurising purposes, the fact that the tubercle bacillus is more 
resistant than the other disease-forms mentioned has caused 
the temperature at which that germ is destroyed to be 
regarded as the proper limit for pasteurisation; and in 
general practice this limit has been a temperature of 155° F- 
for 15-20 minutes. Milk or cream pasteurised at this tem- 
peratuze is, however, rendered much thinner, although the 
amount of fat remains unaltered; the cream on such milk 
does not rise to the surface, and the impression is created 
that the product is deficient in butter-fat owing to the fact, 
discovered by Messrs. Babcock and Russell, in 1896, that in 
milk heated above 140° F. the fat globules become uniformly 
diffused throughout the product, instead of being aggre- 
gated in tiny clots or clusters as is the case in normal milk. 
Some recent investigations of Dr. Theobald Smith* as to the 


* Jnl. of Exp. Med., 1899, p. 217. _ 
