PRESS BULLETIN 122
Florida Agrlcullural Exprlmenl Slallon
SOUR OR ILL-FLAVORED MILK
BY JOHN M. SCOTT
The souring of milk is due to the growth of bacteria. Bacteria are found
in large numbers in the air we breathe, the water we drink, and in the food
we eat. But most of these bacteria are harmless. The special bacteria which
have most to do with the souring of milk are found nearly everywhere. They
cannot be seen without a microscope. One drop of milk may contain as many
as 100,000,000. From this it is easy to understand why we cannot see them as
individuals. However the practical dairyman does not require the assistance
of a high-power microscope to determine whether or not he has undesirable
bacteria about his dairy. The rapidity with which they multiply soon makes
their presence known. Under favorable conditions of food and temperature,
bacteria will double in number every half hour. Fresh milk furnishes ideal
conditions for the growth and development of many kinds of bacteria. It is
for this reason that their effect on milk is so quickly noticed.
HOW TO CONTROL BACTERIA
Most of the bacteria that require the attention of the dairyman grow and
multiply best at a temperature of 80 to 100 degrees Fahrenheit. Some will
grow even at the low temperature of 35 to 40 degrees F., but their growth is
then much slower. A temperature of 135 to 145 degrees F. for a few minutes
will destroy the greater number of bacteria. However there are a few that
can withstand a considerably greater heat. A complete sterilization will re-
quire a temperature of about 220 degrees F. for a few minutes.
Cleanliness is the only way to prevent bacterial contamination-cleanliness
not only in the dairy barn, but also with regard to the dairy utensils and the
milker himself. After the milk is drawn, the temperature should be lowered
as quickly as possible to about 40 degrees F. This low temperature retards
the growth of bacteria, and the milk will keep sweet for a longer period.
HOW BACTERIA AFFECT MILK
There are many changes brought about in milk that are due to the action
of different bacteria. The most common change is the souring and curdling of
the milk. The rapidity with which milk sours, at a given temperature, de-
pends upon the number of bacteria present. The number of bacteria in the
milk depends upon the conditions under which the milk is drawn and kept. As
stated above, bacteria develop and grow faster at summer temperature (80 to
August 21, 1909
100 degrees). Hence if milk is kept at or near this temperature, the bacteria
will develop rapidly, and the milk will sour in a few hours.
We often hear the complaint that the milk has a disagreeable flavor.
This flavor is also imparted to the butter. Such occurrences are annoying
However, in the greater number of cases, sour or badly flavored milk is due
to neglect or carelessness. Milk when drawn from healthy cows is, under
normal conditions, free from these objectionable features. If it is kept under
proper conditions it will remain sweet for a considerable length of time.
When first drawn, milk may have no ill flavor, but after standing for a
few hours may develop a disagreeably bitter taste. This is not always due to
bacteria. Improper feeding, or the use of certain feeds, such as onions or
turnips, is often the cause of the trouble. If it is known that feeds of this
nature have not been given, then the bad taste is probably due to bacteria.
Slimy milk is another trouble that is no stranger to the dairyman. It is
sometimes due to a diseased condition of the cow. But probably, in a major-
ity of cases, it is due to bacteria. There are numerous other troubles familiar
to the dairyman that are due to bacteria, but the above are the commonest
1. Don't let many bacteria get into the milk if you can help it. A little
milky deposit on an imperfectly cleaned can may contain as many bacteria as
the population of the world, ready to infect the fresh milk.
2. Keep the milk cool by the use of ice, or otherwise, so that the bacte-
ria can only grow slowly.
3. If ice is not available and milk has to be kept longer than usual, pas-
teurize it by heating to 140 degrees F. for 20 minutes, and it will keep better.
State papers please copy.