Chapter XVI: Section II: Milk

Milk is a peculiar fluid secreted by the females of all animals belonging to the class _Mammalia_; and, being designed for the nourishment of their offspring, contains all the constituents which enter into the composition of the animal body.

The milk of different animals varies very much in color, taste, and nutritive value. That of the cow is a little heavier than water--its specific gravity being, on the average, about 1.030, water being 1.000. It is composed of three constituents--namely, butter, curd, and whey--each of which is also composed of a number of substances. These three constituents are of unequal weight, or specific gravity, and their separation is the chief process carried on in the dairy. The butter is the lightest and the curd is the heaviest constituent.

The following table represents the composition of the milk of different animals:--

COMPOSITION OF THE MILK OF DIFFERENT ANIMALS.

1,000 PARTS CONTAIN--

------+---------+--------+------------+--------+-------+-------+-------
| Specific| | | | | |
| Gravity,| Water. | Solid | Cheesy | Sugar.|Butter.|Mineral
| or | |Ingredients.| Matter.| | |Matter.
| Density.| | | | | |
------+---------+--------+------------+--------+-------+-------+-------
Woman | 1032.67 | 889.08 | 110.92 | 39.30 | 43.68 | 26.66 | 1.30
Cow | 1030 | 864.20 | 135.80 | 48.80 | 47.70 | 31.30 | 6.00
Goat | 1033.53 | 844.90 | 155.10 | 35.14 | 36.91 | 56.87 | 6.18
Ewe | 1040.98 | 832.32 | 167.68 | 69.78 | 39.43 | 51.31 | 7.16
Mare | 1033.74 | 904.30 | 95.70 | 33.35 | 32.76 | 24.36 | 5.23
Ass | 1034.57 | 890.12 | 109.88 | 35.65 | 50.46 | 18.53 | 5.24
Bitch | 1041.62 | 772.08 | 227.92 | 116.88 | 15.29 | 87.95 | 7.80
------+---------+--------+------------+--------+-------+-------+-------

Milk examined through a microscope is a colorless fluid, containing a large number of little vesicles, or bags, filled with butter--a mixture of oily and fatty matters. When the milk stands for some time, the globules, being lighter than the other constituents, ascend to the top, and, mixed with a certain proportion of milk, are removed as cream. The curd is termed in scientific parlance _casein_, and is in fresh milk in a state of solution--that is to say, is dissolved in milk in the same way that we dissolve sugar in water. When milk becomes sour, either naturally or by the addition of rennet, it can no longer hold casein in solution, and the curd consequently separates. Casein is the substance which forms the basis of cheese. The substance that remains after the removal of the butter and cheese is called _serum_, or whey, and is composed of a sweetish substance termed _sugar of milk_, and certain saline bodies, termed the ash, dissolved in water.

The butter and the sugar of milk are employed in the animal economy in the production of fat, and are what have been styled by physiologists _heat-producers_ and _fat-formers_. The casein resembles the gluten of wheat in composition; it belongs to the class of food substances termed _flesh-formers_. The ash, or mineral part of the milk, is chiefly employed in forming the bones of the young animals it is destined to nourish.

The quality of milk is influenced by the quantity and quality of the food given to the animal. The milk of cows fed on distillery wash, turnip, and mangel tops, coarse herbage, and other kinds of inferior food, is always of inferior quality. Hence it is of great importance that dairy stock be kept in good old pastures in summer, and fed on Swedish turnips, mangel-wurtzel, and oil-cake during winter. It is true economy to supply dairy cows with abundance of nutritious food; and it should be constantly borne in mind that the milk from two well-fed cows will give more butter than can be obtained from the produce of three badly-fed animals.

The butter is the constituent of milk which is most affected by the nature and amount of the animal's food; and butter is precisely the article which is of the greatest importance to the Irish dairy farmer, as the quantity of cheese prepared in this country is inconsiderable. When, therefore, it is found that a cow pastured on inferior land, or badly fed in the byre, yields a large supply of milk of a high specific quantity (which, however, is rarely the case), it must not be concluded that the result is satisfactory; for if such milk be tested by the lactometer it will certainly be found wanting in butter. The average composition of English milk, according to Way, is:--

Water 87.02
Butter 3.23
Casein 4.48
Sugar of milk 4.67
Ash 0.60
------
100.00

In several analyses of milk published by Professor Voelcker, the highest proportion of butter is stated to be 7.62. In that of cows kept on poor and over-stocked pastures less than 2 per cent. was found. I have examined in my capacity of Food Analyst to the City of Dublin several hundred samples of milk, in not one of which have I found the proportion of butter to amount to more than 5.6 per cent. In no sample did I find a higher per-centage of solid matter than 13.15, or (when pure) lower than 12.08. The quality of the food of the milch cow exercises a great influence on the quality and yield of her milk. Aliments rich in fat and sugar favor the production of butter, and augment the supply of milk. Locust-beans, malt, and molasses are good milk-producing foods; but the chief condition in the production of milk rich in butter is simply that the animals which yield it must be fed with abundance of nutritious food. Nor must it be supposed that the richness of milk is due to the smallness of the yield, for whenever the quality of the secretion is inferior, it is almost certain to be deficient in quantity. Those cows which give the richest milk, generally yield the largest quantity.

_Yield of Milk._--According to Boussingault, a cow daily yields on the average 10.4 parts of milk per 1,000 parts of her weight. Morton, in his "Cyclopaedia of Agriculture," p. 621, states that Mr. Young, a Scotch dairy keeper, obtained 680 gallons per cow per annum. Voelcker found that some common dairy stock gave each of them fifty-two pints of milk per diem, whilst three pedigree cows yielded respectively forty-nine pints.

Professor Wilson gives the following information on this point:--

Our principal dairy breeds are the Ayrshire, the Channel Islands,
the Short-horn, the Suffolk, and the Kerry. Some published returns
of two dairies of Ayrshire cows give the annual milk produce per
cow at 650 and 632 gallons respectively. Three returns of dairies,
consisting wholly of Short-horns, show a produce of 540 gallons,
630 gallons, and 765 gallons respectively, or an average of 625
gallons per annum for each cow. In two dairies, where half-bred
Short-horns were kept, the yield was 810 and 866 gallons
respectively for each cow. In four dairies in Ireland, where pure
Kerrys and crosses with Short-horns and Ayrshires were kept, the
annual produce per cow was returned at 500 gallons, 600 gallons,
675 gallons, and 740 gallons respectively; or an average, on the
four dairies, of 630 gallons per annum for each cow. A dairy of
"pure Kerrys" gave an average of 488 gallons per cow, and another
of the larger Irish breed gave an average of 583 gallons per head
per annum. In the great London dairies, now well-nigh extinguished
by the ravages of the cattle disease, these returns are greatly
exceeded. The cows kept are large framed Short-horns and Yorkshire
crosses, which, by good feeding, bring the returns to nearly
1,000 gallons per annum for each cow kept. The custom in these
establishments is to dispose of a cow directly her milk falls
below two gallons a-day, and buy another in her place.

The following milk return of one of our best managed dairy farms
(Frocester Court) shows the relative produce of cows in the
successive years of their milking. The first lot was bought in
at two-years old; all the others at three years:--

No. of Cows. Year of Milk. Produce per head.

8 1st 317 gals.
15 1st 472 "
14 2nd 353 "
15 3rd 616 "
20 4th 665 "
18 5th 635 "
9 6th 708 "
15 Old 651 "

The maximum reliable milk produce that we have recorded was that
of a single cow belonging to the keeper of the gaol at Lewes, the
details of which were authenticated by the Board of Agriculture.
In eight consecutive years she gave 9,720 gallons, or at the rate
of more than 1,210 gallons per annum. In one year she milked 328
days, and gave 1,230 gallons, which yielded 540 lbs. of butter,
or at the rate of 1 lb. of butter to 22-3/4 lb. of milk. In the
early part of the present year (1866) a return was published of
the produce of a cow in a Vermont (U.S.) dairy, which was stated
to have given, in the previous year, a butter yield of 504 lbs.,
at the rate of 1 lb. of butter to 20 lbs. of milk.[25]

_Preserved Milk._--Various plans have been proposed to render milk more portable, and to preserve it sweet for days and even months. Mr. Borden of Connecticut, United States, prepares a concentrated milk by boiling the fluid down in vacuo, at a temperature under 140 deg. Fahrenheit, mixing the resulting solid with sugar, and rapidly placing the compound in tins, which are then hermetically sealed. It is said that solidified milk prepared by this process remains sweet for many months. In France, solidified and concentrated milk are largely prepared; and it is certain that London and other large towns will yet be supplied with milk rendered portable and more stable, by the removal of a large proportion of its water. In many parts of Ireland pure milk could be bought at from 7d. to 8d. per gallon. I do not despair to see factories established in such places for the manufacture of preserved milk as a substitute for the dear and impure fluid sold under the name of milk in London and other large cities. It is stated that solidified milk prepared in Switzerland is now sold in London.