10 
BULLETIN 890, U. S. DEPARTMENT OF AGEICULTUEE. 
ducecl. Preheating also renders the pasteurization more nearly uni- 
form, as the milk goes to the machine at a fairly constant temperature. 
Table 4. — Temperatures of milk at pasteurizing plants that use regenerative 
systems. 
Tem- 
Tem- 
perature 
perature 
Tem- 
perature 
of milk 
as 
received. 
after pre- 
Tem- 
after pre- 
heating 
Degrees 
perature 
cooling 
Degrees 
Plant No. 
by 
regen- 
heated 
by hot 
of milk 
coming 
by 
regen- 
cooled 
bv cold 
erator, 
milk. 
from 
erator, 
raw milk. 
before 
holder. 
before 
going to 
heater. 
going to 
cooler. 
° F. 
° F. 
° F. 
° F. 
° F. 
° F. 
1 
40 
120 
80 
144 
50 
94 
2 
36 
116 
80 
144 
61 
83 
3 
34 
114 
80 
145 
52 
93 
4 
40 
120 
80 
145 
60 
85 
5 
39 
116 
77 
141 
66 
75 
6 
45 
120 
75 
144 
60 
84 
7 
40 
110 
70 
144 
65 
79 
8 
42 
108 
66 
142 
66 
76 
9 
40 
65 
25 
145 
60 
85 
39 
109 
70 
144 
60 
S4 
Note. — The milk regenerative system described in a previous paragraph was used in 
these plants. 
For a complete system of proper pasteurization the following 
equipment must be obtained : 
1. Heater. 
2. Holder. 
3. Cooler. 
In some cases the same apparatus may be used for all three proc- 
esses. 
HEATERS. 
In general, there are two types of heaters, the batch system heater 
and the continuous-flow heater. 
BATCH HEATERS. 
In the batch system the milk is heated in a vat, on the inside of 
which is a coil through which the heating medium, usually hot water, 
is forced. This coil revolves slowly and gently agitates the milk. 
The hot water is either pumped through the coil or forced through 
by air and by the revolving of the coil. 
Another type of batch heater consists of a jacketed tank or vat 
in which the milk is agitated by a mechanical contrivance. Heat is 
supplied by steam or hot water in the outer jacket. Some of the 
older types of vats are provided with disks instead of coils, but 
they are much less satisfactory and are more likely to get out of 
order. It takes from 15 to 30 minutes to heat the milk in the vat 
and after it has reached the desired temperature (145° F.) it is held 
