31. Ever since milk has come to be a commercial product, authorities
have been devising ways in which it may be brought to the consumer in a
condition that will permit it to be used without causing ill results.
Their efforts have been rewarded to such an extent that nowadays
consumers have little to fear from the milk they purchase, provided they
get it from dealers who live up to the laws. Chief among the different
grades of clean milk is _certified milk,_ and next in order comes
_pasteurized milk,_ followed by _sterilized milk_.
32. CERTIFIED MILK.--The grade of clean milk sold under the name of
certified milk is simply natural, raw milk that is produced and marketed
under conditions that permit it to be guaranteed as pure, wholesome, and
of definite composition. Such milk is necessarily higher in price than
milk that is less wholesome and sanitary, because of the extra cost to
the dairyman in meeting the requirements that make it possible for him
to produce clean milk under sanitary conditions. These requirements
pertain to the health and cleanliness of those who handle the milk, to
the health, housing condition, and care of the herd and the dairy cows,
and to the handling and care of milk in the dairy and during
transportation and delivery. They are usually established and enforced
by an inspection commission appointed by the city, county, or state in
which the milk is produced.
33. If a little careful thought is given to the milk situation, it will
be admitted that such precautions are necessary if clean milk is to be
the result. Such milk cannot be produced if the surroundings are dirty,
because dust and flies, which are two sources of contamination, are
practically always present in such places. A stable with poor
ventilation, without screens to keep out flies, and with floors that
will not permit of cleaning, but cause filth and refuse to accumulate,
is sure to contaminate milk that is handled in it. In addition, cows
that are not well fed, comfortably housed, or carefully groomed cannot
be expected to give milk of as good quality as cows that are properly
cared for. Likewise, if the persons who do the milking are not clean,
the milk is subject to contamination from this source.
34. All such unfavorable conditions can be remedied, and must be in the
production of certified milk; but the good accomplished in this
direction will be lost if the milk is carelessly handled after milking.
Therefore, in producing certified milk, only the cleanest water
available is allowed to be used in the dairy. Impure water is a common
source of the contamination of milk in such places. On some farms, the
water supply comes from a well that is too near the barn or that is too
shallow to avoid being made impure by the germs that filter into it from
the barnyard or a cesspool. If vessels in which milk is placed are
washed in such water, it is necessary to sterilize them by boiling or
steaming before milk is put into them, in order to kill the germs that
come from the water. If such a precaution as this is not observed, the
germs will multiply rapidly in the milk and, provided they are
disease-producing, will make the milk extremely dangerous.
Besides observing the precautions mentioned, it is necessary that all
utensils used in a dairy, such as pails for milking, strainers,
containers, etc., be kept scrupulously clean. Likewise, they must be
sterilized by boiling each time they are used, for, while disease germs
may be absent, those which cause the milk to sour are always present and
must be destroyed. Finally, to prevent any germs that enter milk from
multiplying, even when it is properly cared for, the milk has to be
cooled to a temperature of 45 degrees Fahrenheit or lower immediately
after milking and then bottled in sterilized bottles, sealed, and packed
in ice, within 20 minutes after milking.
35. It is by giving attention to all such matters that certified milk is
possible. Such milk, as will be understood from what has been said, is
neither a cooked milk nor a dirty milk that is processed, but a natural,
raw milk that is clean at all stages of its production and marketing.
Because of this fact, it is the best and cleanest milk to be had and may
be used without hesitation, not only by grown persons in good health,
but for infants and invalids.
The sanitary condition of certified milk and the consequent length of
time it will remain sweet was demonstrated conclusively as far back as
1900 at the Paris Exposition. At this time, two model dairies in the
United States--one located at the University of Illinois and the other
at Briarcliff Manor, Westchester County, New York--delivered to their
booths at the Exposition milk that was bottled under the most sanitary
conditions at their dairies. During its transit across the ocean the
milk was kept at a temperature of 40 to 42 degrees Fahrenheit, and on
its arrival, 2 weeks after leaving the dairies, it was found to be in a
perfectly sweet condition. Similar experiments made at later dates, such
as shipping certified milk from the East to California, serve to bear
out the test made in 1900, and prove what can be done with milk so
produced as to be as free as possible from bacteria or the conditions
that permit their growth.
36. PASTEURIZED MILK.--While certified milk is undoubtedly the safest
kind of milk to use and is constantly growing in favor, much of the milk
received in the home is pasteurized. By pasteurized milk is meant milk
that has been heated to a temperature of 140 to 155 degrees Fahrenheit,
kept at this temperature for 15 to 20 minutes, and then cooled rapidly.
The result of such a treatment is that any disease-producing germs that
are present in the milk, as well as those which are likely to cause
intestinal disturbances, are destroyed, and that the milk is rendered
safe as food for a time. Pasteurizing does not materially change the
taste of milk, nor does it seriously affect the digestive properties of
this food. It is true, of course, that pasteurized milk is not so good
as clean raw milk. Still it is better to use such milk than to run the
risk of using milk that might be contaminated with the germs of
tuberculosis, typhoid fever, scarlet fever, diphtheria, or any other of
the numerous diseases that have been known to be carried to whole
families and communities through the milk supply.
37. Although pasteurizing is done on a large scale in dairies, there is
no reason why the housewife cannot pasteurize the milk she buys,
provided it is raw milk and she feels that it is not safe to use. If
pasteurizing is to be done frequently and large quantities of milk are
to be treated, it would be advisable to purchase the convenient
apparatus that is to be had. However, if only a small quantity of milk
is to be pasteurized at a time, a simple improvised outfit will prove
satisfactory, because milk pasteurized in the home may be heated in the
bottles in which it is received. Such an outfit consists of a dairy
thermometer, a deep vessel, and a perforated pie tin or a wire rack of
suitable size.
38. To pasteurize milk in the home, proceed in the manner illustrated
in Fig. 3. Place the rack or invert the perforated pie tin in the bottom
of the vessel, and on it place the bottles of milk from which the caps
have not been removed. Make a hole through the cap of one bottle, and
insert the thermometer into the milk through this hole. Then fill the
vessel with cold water to within an inch or so of the top of the
bottles, taking care not to put in so much water as to make the bottles
float. Place the vessel over the fire, heat it until the thermometer in
the bottle registers a few degrees over 150 degrees Fahrenheit, and keep
the milk at this temperature for 15 to 20 minutes. At the end of this
time, the milk will be sufficiently pasteurized and may be removed from
the fire. As soon as it is taken from the water, cool it as rapidly as
possible by running cold water into the vessel slowly or by placing the
bottles in several changes of water, taking care not to place the hot
bottles in very cold water at first, as this may cause them to crack.
[Illustration: Fig. 3]
When the milk has been cooled by some rapid method, keep it cool until
it is used. This precaution is necessary because of the nature of
pasteurized milk. The temperature at which milk is pasteurized is
sufficient to kill all fully developed bacteria, but those which exist
in an undeveloped state, or in the form of spores, develop very rapidly
after pasteurization unless the milk is kept cold and clean. If these
bacteria were allowed to develop, the purpose of pasteurization would be
lost, and the milk would become as dangerous as it was originally. The
advantage of cooling milk rapidly will be fully appreciated upon
referring to Fig. 4, which illustrates the development of a single germ
in milk that is cooled rapidly and in milk that is cooled slowly.
[Illustration: Fig. 4]
39. STERILIZED MILK.--By sterilized milk is meant milk in which all
germs are destroyed by sterilization. Such milk is not sold by dealers,
but the process of sterilization is resorted to in the home when
pasteurization is not sufficient to render milk safe. This process,
which is the only positive means of destroying all germs, consists in
bringing the milk to the boiling point, or 212 degrees Fahrenheit,
allowing it to boil for three quarters of an hour, and then cooling it
rapidly. One who undertakes to treat milk in this way should remember
that it is difficult to boil milk, because the solids in the milk adhere
to the bottom and sides of the vessel and soon burn. However, this
difficulty can be overcome by sterilizing the milk in the bottles in
which it is bought.
40. To sterilize milk, place the sealed bottles on a wire rack or a
perforated pie tin in a deep vessel, as for the pasteurizing of milk,
and pour cold water into the vessel until it nearly covers the bottles.
Then raise the temperature of the water quickly to the boiling point,
and after it has begun to bubble, allow it to boil for three quarters of
an hour. At the end of this time, cool the milk rapidly and then keep it
cool until it is used.
41. Although milk thus treated becomes safe, sterilization changes its
flavor and digestibility. If milk of this kind must be used, some raw
food should be given with it. A diet composed entirely of cooked food is
not so ideal as one in which some raw food is included, because raw
foods contain substances that are essential to health. The change that
takes place in the composition of milk that has been sterilized can be
easily observed. Such milk on becoming sour does not coagulate as does
pasteurized or raw milk, owing to the fact that the lime salts in the
milk are so changed by the high temperature as to prevent the thickening
process from taking place. Then, too, sterilized milk is not likely to
become sour even after considerable time. Still, such milk is not safe
to use except when it is fresh, for instead of fermenting in the usual
way it putrefies and is liable to cause such a dangerous sickness as
ptomaine poisoning.
42. MODIFIED MILK.--For infants who cannot be fed their normal diet,
cow's milk must be used as a substitute, but in order to make it a more
nearly ideal food for them it must usually be modified, or changed, by
adding other materials. When it is so treated, it is known as modified
milk. The materials used to modify milk are sterile water, lime water,
barley water, cream, skim milk, milk sugar, or some other easily
digested carbohydrate, one of these or a combination of them always
being employed. The proportion of these ingredients to use varies with
the age of the child that is to be fed and must be constantly changed to
meet the child's requirements. In the production of modified milk, a
physician's prescription and directions should always be followed
closely. Only the best quality of milk should be used, and, in addition,
the greatest care should be taken to have all the bottles, utensils, and
materials used as clean and sterile as it is possible to make them. If
such conditions cannot be met, it is advisable to pasteurize the
modified-milk mixture after the materials have been put together.