temperature is
favorable to growth of the bacteria that are sought, the gas-forming
organisms. At the end of ten to twelve hours, the jars are examined;
if the curd is solid, the texture firm, not mushy or slimy on the
surface, if the odor is agreeable, it indicates that the milk
contains few or none of the undesirable forms of bacteria. If the
curd is full of gas holes, it is apparent that undesirable bacteria
are present and under such circumstances the curd will not have an
agreeable odor. If the gas-forming bacteria are numerous, the curd
may even be spongy from the abundance of gas holes, and the
undesirable odor more pronounced. Such curds are tough and rubbery.
In some cases a bad flavor or odor is apparent even though the
texture of the curd is not open and full of holes. The curd, the
surface of which is slimy indicates undesirable organisms. A solid
curd of agreeable odor is indicative of the presence of the
desirable acid-forming bacteria. Such a milk is excellent from the
standpoint of the butter or cheese maker, but may not be so
desirable from the standpoint of the milk dealer on account of its
poor keeping qualities. On the other hand a milk suitable from the
standpoint of the milk dealer, on account of its low germ content,
and hence good keeping quality, may give a poor curd test. It is
certain to contain some bacteria, especially those from the interior
of the udder while it may contain none of the desirable acid-forming
organisms without which a curd of good texture and flavor can not be
obtained. The bacteria in the clean milk will grow rapidly at the
high temperatures at which the curds are kept and the changes they
will produce as to flavor and odor may be undesirable. The milk
might be judged as poor when in reality it might be a most excellent
sample, and if kept at the ordinary storage temperatures, it might
keep for days. The test when used for market milk should be
interpreted with this in mind.

[Illustration: Fig. 24.--Curd Test.

The curd obtained from milk containing many gas-forming bacteria.
The irregular, angular holes are mechanical, due to the imperfect
fusion of the pieces of curd.]

If the results are to be of any value, the test must be made with
care to avoid all sources of error; the tester must know that the
bacteria causing the gas and bad flavors in the sample were
originally present in the milk at the time the sample was taken, and
that they have not come from the contai