FERMENTED MILKS 13 
discarded as it serves to wash off the lip. The care necessary to 
maintain a pure starter of L. acidophil/us can not be overemphasized. 
The starter should be examined frequently for purity either micro- 
scopically or by plates. Should it develop a bad flavor or odor, it 
must be discarded and a new culture obtained. In any case it is 
advisable to get a new culture at regular intervals. Kopeloff advises 
the use of a new fecal culture every two to four months to assure the 
therapeutic value of the product. 
The bulk starter, which is the starter to be used to inoculate the 
batch, is prepared in the same way as the mother starter; and the 
same precautions against contamination must be observed. Florence 
or Erlenmeyer flasks of 2-liter capacity or larger are most satisfac- 
tory in which to prepare this bulk starter. These flasks permit the 
autoclaving of the milk and are most easily handled under the condi- 
tions necessary to prevent contamination. The starter should be 18 
to 24 hours old when used to inoculate the batch and should possess 
all the. qualities indicating purity previously mentioned for the 
mother starter. 
Equally as great care must be exercised in the treatment of the 
milk as in the preparation of the starter. Only fresh milk of the 
best quality should be used hi the manufacture of acidophilus milk. 
Whole milk, milk which is partly skimmed, or skim milk may be 
used. The pasteurizer employed in the preparation of the product 
must be so fitted that the milk may be heated and cooled without 
removing it from the vat, which should be equipped with an efficient 
mechanical stirrer. The vat must be used not only as a pasteurizer 
but also as an incubator for the milk. The characteristics of the 
bacterium Lactobacillius acidophilus make it necessary that the bac- 
teria in the milk be killed before the starter is added. The milk is 
heated to about 205° F. for an hour and a half or longer and then 
" cooled to 98°. It should have a slightly caramelized appearance after 
heating ; however, this in itself is not an indication that the necessary 
destruction of the bacteria has been accomplished. Bass (3) recom- 
mends heating the milk to 190° to 195° for one hour; then cooling 
it to 98°, at which temperature it is held for three or four hours; 
again heating it to 190° to 195° for one hour; then cooling it to 98° ; 
and inoculating. After the milk has been cooled to 98° to 100° it is 
inoculated with about 2 per cent of the bulk starter. The greatest 
care must be observed in the inoculating process to prevent the con- 
tamination of the batch. The mouths of the flasks should be passed 
through a flame before pouring the starter. The cover of the vat 
is lifted just sufficiently to permit the pouring of the starter and is 
replaced immediately. After inoculation the milk is stirred for a 
few minutes to distribute the inoculum, and the batch is then allowed 
to incubate. The temperature of incubation, 98° to 100°, should 
be maintained throughout the entire incubation period. The batch 
is incubated until a firm curd has been formed, which usually re- 
quires about 18 to 24 hours. The length of the incubation period 
is dependent upon the size of the inoculation, the temperature of 
incubation, and the activity of the starter. After the milk has 
curdled it is broken up by stirring, cooled to room temperature, and 
bottled. According to Kopeloff (51), acidophilus milk should be 
held at room temperature to preserve the largest number of viable 
