12 BULLETIN 342, TJ. S. DEPARTMENT OF AGRICULTURE 
A study of 404 municipal ordinances, made in 1928 (Table 5), shows 
that cities in the population groups from 50,000 up to and including 
500,000 and over are very uniform in their requirements for pasteur- 
ization. The temperature requirements range from 140° to 145° F., 
with the majority of the cities using 142°. The lengths of time for 
which the milk is required to be held at these temperatures are even 
more uniform, with 97 of the 99 cities studied requiring 30 minutes. 
The cities in the groups 10,000 and less, 10,000 to 25,000, and 25,000 
to 50,000 show more variation in temperature and length of time re- 
quired. However, disregarding the cities in these groups that have 
no requirements, nearly half of the others require a temperature of 
142° and the greater number require 30 minutes as the time of holding. 
Results of studies made upon continuous-flow holders, both under 
actual commercial conditions and in the laboratory, indicate that 
careful qualitative bacteriological analysis should be made of the milk 
pasteurized by this method. It must be remembered that a low-count 
milk is not always a safe milk. If an apparatus is used which pro- 
duces a low-count milk but which does not hold every particle of milk 
at pasteurization temperature for at least 30 minutes, such apparatus 
should be viewed with distrust, for the safety factor is not assured. 
In many instances the actual flow through the machine does not coin- 
cide with the theoretical flow. The holder process has almost entirely 
replaced the flash process, and is the one most used in the United 
States. 
Pasteurization in the bottle was developed several years ago, but 
has not come into generalise. Under this system the bottles of milk, 
usually in the cases, are placed in a compartment where the milk is 
heated to the required temperature, and then held and cooled. By 
some types of bottle pasteurization the bottles of milk are removed 
from the cases and then conveyed slowly through the machine, being 
heated at the beginning and cooled at the end of the process. The 
heating is usually accomplished by passing sprays of hot water over 
the bottles or by immersing them in tanks filled with water of tempera- 
ture high enough to heat the contents to the pasteurization tempera- 
ture. Either a special water-tight cap is used or the bottles are 
covered with a specially constructed pan in which there are small 
holes through which the hot water passes and forms a thin film around 
the bottles. The advantage of this process lies in the fact that the 
milk, after being heated, is not exposed until it reaches the consumer, 
and any danger of contamination through handling is therefore elimi- 
nated. However, the cost of pasteurizing under this system is greater 
than that of bulk pasteurization, for steam and refrigeration are 
required to heat and cool the bottles and cases as well as the milk. 
Furthermore, extra space and more handling are necessary. 
