14 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE 
ADVANTAGES OF LOW-TEMPERATURE PASTEURIZATION 
In general, the trend of pasteurization has been toward the holder 
process, and with this tendency the use of lower temperature has be- 
come more common. As a general rule, when the holder process is 
used the milk is heated to not less than 142° F. for 30 minutes. 
From bacteriological, chemical, and economic standpoints, the present 
consensus is that pasteurization can be satisfactorily accomplished 
with a temperature as low as 142°. 
From a bacteriological standpoint, pasteurization at 142° F. for 
30 minutes is believed to kill all nonspore-forming disease-producing 
bacteria, and at the same time leave in the pasteurized milk the maxi- 
mum percentage of the bacteria that cause milk to sour (lactic-acid 
bacteria) and only a small percentage of those that cause it to decom- 
pose (peptonizers). When higher temperatures are used the total 
number of all kinds of bacteria is reduced, but the percentage of lactic- 
acid bacteria becomes less and less and the peptonizing group increases 
until at 180° or above, the lactic-acid bacteria are practically all de- 
stroyed and most of the bacteria left belong to the peptonizing group. 
The heat-resistant lactic-acid bacteria which survive pasteurization 
at 142° for 30 minutes play an important role in the souring of com- 
mercially pasteurized milk. m 
From a chemical standpoint, the advantage of the lower tempera- 
ture is that milk pasteurized at 142° F. for 30 minutes does not undergo 
any appreciable change affecting its nutritive value or digestibility. 
According to Rupp (50) the soluble phosphates of lime and magnesia 
do not become insoluble and the albumin does not coagulate. At 
150° about 5 per cent of the albumin is rendered insoluble, and the 
percentage increases with higher temperatures up to 160°, when about 
30 per cent of the albumin is coagulated. The heating period in 
Rupp's experiments was 30 minutes. 
From an economic standpoint the advantage of pasteurization at 
low temperatures is the saving in the cost of heating and cooling the 
milk. Bowen (15) has shown that the flash process requires approxi- 
mately 17 per cent more heat than the holder process. Also there is 
a correspondingly wider range through which the milk must be cooled, 
which also adds to the cost. This is because of the fact that in the 
holder process milk may be heated to 142° F. and held for 30 minutes, 
whereas to obtain the same bacteriological reduction with the flash 
process, with 1 -minute heating, the milk would have to be heated to 
165°, and even then it is doubtful whether all the disease-producing 
bacteria would be killed. 
TEMPERATURES AND METHODS MOST SUITABLE FOR PASTEURIZING 
It has been found that heating milk at 140° for 30 minutes will kill 
pathogenic bacteria, provided all the milk is heated to that point and 
held for the full length of time. But it has been shown by Schorer 
and Rosenau (52, p. 157) that it is difficult to do this under com- 
mercial conditions. These investigators inoculated milk with Bacillus 
diphtheriae, B. typhi, and B. tuberculosis and pasteurized it in 100- 
gallon lots under commercial conditions. They found that sometimes 
not all of the organisms were killed, and in this connection state : 
Nothing in our experiments throws doubt upon the thermal death points of the 
microorganisms tested. We are sure that if the milk reaches 140° F. and is held 
