COMPOSITION OF MILK.
The composition of milk, though frequently discussed, is not generally
well understood. It is quite variable, not only in the milk from
different cows, but in that from the same cow at different times, and in
different conditions, but especially at different seasons of the year.
It is more buttery in winter, and more cheesy in summer. A cow milked
three times a day would give more in quantity but poorer in quality,
than if milked twice; while one milked twice a day will yield more milk
than if milked once a day, but one milking a day would be the richer.
The first milk drawn from the udder is more watery than what follows;
the last is the richest. The accumulation of milk in the cow's bag is
influenced by the law of gravitation. The water being the heaviest
ingredient, settles to the bottom, and is the first milked; the cream,
which is the lightest, rises, and is the last milked. That is to say, a
partial separation takes place in the udder, sufficient to make the
"strippings" some ten or twelve times as rich in butter as the first
milk drawn. We would, therefore, infer that the first third contains the
most water, the second third the most cheese, and the last third the
most butter. There is said to be a difference in the milk drawn from the
compartments of the udder of the same cow, or from different teats.
The variation in the composition of milk, of course, is indicated by
different chemical analyses, no two of which can be found to exactly
agree. We give an analysis by HAIDLEN. He found that the specimen
contained, in 1,000 parts, 873 parts of water, 30 of butter, 48.2 of
cheese, 43.9 of sugar of milk, 2.31 of phosphate of lime, .42 of
magnesia, .47 of iron, 1.04 of chloride of potassium, and .66 of sodium
and soda. Other chemists have found albumen among the constituents of
milk, and this ingredient is believed, by many, to be the one that first
commences decaying, in hot weather, and produces, "tainted" milk,
"floating" curds, and "huffy" cheese. Skimmed milk has been found, in
some instances, to contain as high as 97 parts of water in 100, and only
3 per cent. of solids, or cheesy matter. "Swill milk" has been found to
contain as low as 1½ per cent. of butter. An analysis of the first milk
taken from a cow's bag after calving, showed it to consist of 15.1 per
cent. of caseine, or cheese, 2.6 of butter, 2 of mucous matter, and 80.3
of water. Ordinary pure milk will average about 12½ per cent. of cream.
But it is not unfrequently found to yield 15 to 20 per cent., and even
as high as 25 per cent. of cream has been obtained. If milk yields less
than 10 per cent. of cream, it is below the average, and unprofitable
for butter-making.
We know of no single instrument that will at once indicate the quality
of milk. What is called the lactometer, but is properly a hydrometer,
will indicate the density of milk, and if its specific gravity in a pure
state be known, it will show the amount of water added, if any. On an
average, milk is about 4 per cent. heavier than water. That is, a
hydrometer with a scale graded at 100 for milk at 60° Farenheit, ought
to sink to 96 in water. The variation in the density of milk will be
shown by an experiment given by CHARLES L. FLINT, in his "Milch Cows and
Dairy Farming." He says:
"For the purpose of showing the difference in the specific gravity of
different specimens of pure milk, taken from the cows in the morning,
and allowed to cool down to about 60°, I used an instrument graduated
with the pure milk mark at 100, with the following results: The first
pint drawn from a native cow stood at 101. The last pint of the same
milking, being the strippings of the same cow, stood at 86. The mixture
of the two pints stood at about 93½. The milk of a pure bred Jersey
stood at 95, that of an Ayrshire at 100, that of a Hereford at 106, that
of a Devon at 111, while a thin cream stood at 66. All these specimens
of milk were pure, and milked at the same time in the morning, carefully
labeled in separate vessels, and set upon the same shelf to cool off;
and yet the variations of specific gravity amounted to 25, or, taking
the average quality of the native cow's milk at 93½, the variations
amounted to 17½."
It will be seen, by these experiments, that the richer the milk in
butter, the less the specific gravity, thin cream being 30° below the
water mark. The richer the milk in caseine, or cheese, the greater the
specific gravity, the milk of the Devon indicating 15° above the water
mark. Watering milk will of course reduce the specific gravity of milk
rich in cheese, and by this means it can be made to indicate the average
density of pure milk. In the same way, milk rich in butter may have its
specific gravity increased until it nearly reaches that of water, but no
amount of watering can make it indicate over 96°, which is the figure
given for pure water. A little salt, or other ingredient, may be added
to bring the density up to the pure milk mark. So the blueness of milk,
produced by either skimming or watering, may be removed by the use of
burnt sugar, which will give it a rich color. Or annotto may be used
for the same purpose. Many expedients have been resorted to, from time
to time, by the dishonest, for the purpose of disguising the
impoverishment of milk by skimming and watering.
"But," says some one, "why tell dishonest men how they can skim and
adulterate their milk?" We have not done so. We have told honest men
some of the practices of the dishonest, with the view of enabling them
to detect the fraud. True, the hydrometer is not an accurate or legal
test; but it shows the exact density of the milk tried, and this is a
very important point. When you have decided this, by the use of the
cream-gauges, you can determine the amount of cream; and if you let the
milk stand until it coagulates, and the cheese separates from the whey,
you can tell the relative proportion of water and cheese. This may be a
somewhat slow and clumsy process, but it is nevertheless decisive, and
often repays the trouble. Foreign substances, so far as not held in
solution by the water, or not entangled in the cheese or cream, will
settle at the bottom of the glasses. Besides, with these evidences to
start on, the ways of a suspected person can be watched, and he often be
caught in the very act of violating the law, which we quote below:
§ 1. Whoever shall knowingly sell, supply, or bring to be
manufactured to any cheese manufactory in this State, any milk
diluted with water, or in any way adulterated, or milk from which
any cream has been taken, or milk commonly known as skimmed milk;
or whoever shall keep back any part of the milk known as
"strippings;" or whoever shall knowingly bring or supply milk to
any cheese manufactory that is tainted or partly sour from want of
proper care in keeping pails, strainers, or any vessel in which
said milk is kept, clean and sweet, after being notified of such
taint or carelessness; or any cheese manufacturer who shall
knowingly use, or direct any of his employes to use, for his or
their individual benefit, any cream from the milk brought to said
cheese manufacturer, without the consent of all the owners thereof,
shall, for each and every offense, forfeit and pay a sum not less
than twenty-five dollars, nor more than one hundred dollars, with
costs of suit, to be sued for in any court of competent
jurisdiction, for the benefit of the person or persons, firm or
association or corporation, or their assigns, upon whom such fraud
be committed.