21. So far as the housewife is concerned, the qualities that
characterize wholesome milk are without doubt of great interest. She may
know of what use milk is in the diet and the food substances of which it
is composed, but unless she understands just what constitutes milk of
good quality, as well as the nature of inferior milk, she cannot very
well provide her family with the kind it should have. Therefore, to
assist her in this matter, the characteristics of wholesome milk are
here discussed. Such milk, it will be well to note, must be of the right
composition, must not be adulterated, must be fresh--that is, not older
when delivered than is permitted by law--and must be as clean
as possible.
22. STANDARD OF MILK COMPOSITION.--The housewife usually judges the
quality of milk by the amount of cream that rises to the top when milk
in a bottle is allowed to remain undisturbed for some time. This is
really an excellent test, because milk that contains only a small amount
of cream is of poorer quality than that which contains a larger amount;
in other words, the more cream milk contains, the higher will be its
food value and the greater its energy-producing ability. Then, too, milk
that is rich in cream usually contains proportionately large amounts of
protein and sugar.
While the composition of milk has much to do with the quality of this
food, it varies, as should be noted, in different breeds and even in
individual cows, depending on both the food and the care given to them.
For this reason, milk that is mixed is preferable to the milk of a
single cow, as the mixing of the milk of a number of cows insures a
better average composition.
23. ADULTERATION OF MILK.--The composition of milk, and hence its
quality, is seriously affected by its adulteration. By this is meant the
extraction of any of the food substances from whole milk; the addition
of anything that tends to weaken or lower its quality or strength; the
use of coloring matter to make it appear of greater value than it
actually is; or the use of preservatives to prevent it from souring as
soon as it ordinarily would. It is, of course, illegal to adulterate
milk, yet it is sometimes done. The most convenient and possibly the
most common materials used to adulterate milk are water and skim milk.
The addition of water to milk decreases the quantity of all its food
substances, but the addition of skim milk reduces the quantity of fat
only. The color of the milk is often affected by the use of these
adulterants, but when this happens, yellow coloring is usually added to
restore the original appearance.
Sometimes the milk that a dairyman markets contains more fat than the
law requires; but even such milk cannot legally be skimmed nor diluted
with skim milk. The only thing that may be done to it is to mix it with
milk that is low in butter fat and thus obtain a milk that will average
the legal percentage. For instance, if milk from a dairy averages 5 per
cent, of butter fat, it may be diluted with milk that contains only 3
per cent, of butter fat, because the result of such mixing, which will
be milk averaging 4 per cent, of this food substance, will be the
legal standard.
24. To prevent milk from souring, dishonest milk dealers often put into
it such preservatives as soda, borax, and formaldehyde. There is no
definite way of telling whether or not one of these has been used,
except by a chemical analysis. However, if milk does not sour within a
reasonable time when no precautions have been taken to keep it sweet, it
should be looked on with suspicion, for it undoubtedly contains a
preservative.
25. FRESHNESS OF MILK.--To be most satisfactory for all purposes, milk
should be absolutely fresh. However, it is almost impossible to obtain
milk in this condition, because it is generally sold at a distance from
the source of supply. Milk that is sold in small towns and cities is
usually 12 and often 18 to 21 hours old when it is delivered; whereas,
in large cities, where the demand is so great that milk must be shipped
from great distances, it is often 24 to 36 or even 48 hours old when it
reaches the consumer. In order that milk may remain sweet long enough to
permit it to be delivered at places so far removed from the source of
supply, it must be handled and cared for in the cleanest possible way by
the dealers. Likewise, if the housewife desires to get the best results
from it, she must follow the same plan, cooling it immediately on
delivery and keeping it cool until it is consumed. The freshness of milk
can be determined only by the length of time it will remain sweet when
proper care is given to it.
26. CLEANLINESS OF MILK.--Milk may be of the right composition, free
from all adulteration, and as fresh as it is possible to obtain it, but
unless it is clean, it is an injurious food. Milk is rendered unclean or
impure by dirt. In reality, there are two kinds of dirt that may be
present in milk, and it is important to know just what these are and
what effect they have on milk.
27. The less harmful of the two kinds of dirt is the visible dirt that
gets into the milk from the cow, the stable, the milker, the milking
utensils, and similar sources when these are not scrupulously clean. If
milk containing such dirt is allowed to stand long enough in pans or
bottles for the heavier particles to settle, it will be found as
sediment in the bottom of the receptacle. To say the least, the presence
of such dirt is always disagreeable and frequently produces
foreign flavors.
Straining the milk through clean absorbent cotton will reveal the
presence of such dirt and another kind of dirt that does not show
through the opaque fluid. This second kind of dirt is generally found in
milk when the first kind is present in any quantity. It is more liable
to be harmful than the other, because it enters the milk from the water
used in cleaning the receptacles or from some contaminated source.
[Illustration: FIG. 2]
28. Whenever dirt is present in milk, bacteria are sure to be there; and
the greater the quantity of dirt the greater will be the number of
bacteria. Should the housewife desire to compare the cleanliness of
several lots of milk, she may filter a like quantity from each lot, say
a quart or a pint, through small disks of absorbent cotton. If, after
the milk has passed through the cotton disk, very little dirt remains on
it, as in Fig. 2 (_a_), the milk may be considered as comparatively
clean; if the cotton disk appears as in (_b_), the milk may be said to
be only slightly dirty; if it appears as in (_c_), the milk is dirty;
and if it appears as in (_d_), the milk is very dirty. Milk that leaves
a stain like that in (_d_) contains more bacteria than milk that leaves
a stain like that in (_c_), and so on through all the lots of milk.
Filtering milk in this manner, however, does not indicate whether the
bacteria are disease producing. Such information can be secured only by
microscopic examination, and only then by persons who have a knowledge
of such matters.
29. Since, as has been pointed out, bacteria cling to all dirt, the
dirt that milk contains is one of the causes of souring and putrefaction
of milk, and may be a cause of disease. Indeed, it is definitely known
that dirty milk sours much more quickly than does clean milk. Actual
tests in which clean milk was put in a cool place have proved that it
will keep for weeks, whereas dirty milk will sour in a day or two,
especially in warm weather. This information should point out clearly to
the housewife that it is not merely heat that changes milk or causes it
to sour. She should understand in addition, that bacteria grow and
multiply very rapidly when conditions for their growth are provided.
These conditions are moisture, warmth, and the right kind of food, and
as all of these are found in milk, this product is really ideal for
bacterial development. The only way in which to protect milk is to make
sure that no bacteria enter it, or, if they do, to make it impossible
for them to grow. This may be done by keeping the milk so cold that they
cannot thrive, or by destroying them in various ways, which are taken
up later.
30. In former times, there was not much danger of wide-spread disease
from the milk supply, for it was cared for almost entirely by those who
kept a few cows and distributed milk to a small number of customers. In
fact, it has been only within the past 50 years that large quantities of
milk are handled by separate dairies and shipped great distances from
the source of supply and that the distribution of milk has become a
great industry. When so much milk is handled in one place, it is more or
less unsafe unless the dairy is kept extremely clean and is conducted in
the most sanitary manner. Experience has shown that too much attention
cannot be given to the care of milk, for the lives of great numbers of
children have been sacrificed through the carelessness of dairymen and
persons selling and distributing milk, as well as through the negligence
of those who handle the milk after it has entered the home. To overcome
much of this carelessness, both the Federal Government and the various
states of this country have set standards for safe milk production, and
in order to make their laws effective have established inspection
service. Independently of these state and national laws, many of the
cities, particularly the large ones, have made their own standards,
which, as a rule, are very rigid. One of the usual requirements is to
compel each person who wishes to sell milk in the city to buy a license,
so that the city authorities may keep in touch with those handling milk
and so that conditions may be investigated at any time. In view of the
care required of dealers in handling milk, the housewife owes it to
herself and the members of her family to keep the milk in the home in
the best possible manner.