10 
BULLETIN 890, U. S. DEPARTMENT OF AGRICULTURE. 
duced. 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 
after pre- 
Tem- 
after pre- 
heating 
Degrees 
perature 
cooling 
Degrees 
Plant No. 
by 
heated 
of milk 
by 
cooled 
regen- 
by hot 
coming 
regen- 
by cold 
received. 
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 
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 
84 
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. 
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 in the same vat for 30 minutes. The vat should be well insulated 
to prevent loss of heat during the holding process. The coils are some- 
times allowed to revolve during the holding process so that the cream 
will not rise and the milk will be held at a more uniform temperature. 
