22 BULLETIN 890, U. S. DEPARTMENT OF AGRICULTURE. 
Some of the advantages of pasteurizing in the bottle are : 
1. Operation is comparatively simple. 
2. For a small dealer the first cost is comparatively small. 
3. The apparatus is durable. 
4. There is little chance of recontamination of the milk after pasteuriza- 
tion, provided water-tight caps are used and bottles do not have to be 
recapped. 
5. The bottle as well as the milk is heated. 
6. In some cases small plants can save space by its use, as the pasteur- 
izer serves also as a cold-storage room. 
7. No apparatus, pumps, or pipes to clean. 
Some of the disadvantages of in-the-bottle pasteurization are : 
1. The system is rather slow for a large commercial plant. For a small 
plant, however, this objection may not be serious. 
2. Considerable extra steam and refrigeration are required, as it is 
necessary to heat and cool the bottles, caps, and cases, in addition to 
the milk. 
3. During the heating process the milk will expand in the bottle, so that 
unless a bottle of extra capacity or a special and more expensive cap is 
used, many of the bottles will have to be recapped after cooling, because 
the expansion of the milk will force the cap out. It is advisable to use 
a bottle of extra capacity, since recapping, besides causing considerable 
trouble, may contaminate the milk. Where extra-sized bottles are used 
they contain full measure of milk, but there is some empty space between 
the top surface of the milk and the cap to allow for expansion during heat- 
ing. Such bottles do not appear full when delivered and thus may cause 
some complaint among customers. 
SYSTEMS OF PASTEURIZING USED. 
Various systems of pasteurizing used at 237 plants are shown in 
Table 5. It will be noted that the vat and in-the-bottle systems are 
more common with the smaller plants, while film and tubular types 
are more common with the medium-sized and large plants. Seventy- 
five of the 237 plants were using temperature recorders, and 67 plants 
were using temperature regulators. 
One of the important factors in a pasteurization system is an even 
flow of milk into the pasteurizer and also from the holder to the 
cooler. If the flow is constant throughout the apparatus more ac- 
curate results will be obtained. At some plants where a gravity sys- 
tem is used a float valve is attached to the apparatus. This valve 
will allow only a certain quantity of milk to flow to the pasteurizer 
per hour. A similar valve placed at the outlet of the holder will 
a] low the same quantity to go from the holder per hour. In this way 
more nearly uniform results are obtained in heating and holding. 
