Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/322

304 MILK 500 gallons of milk, from which nearly 500 Bb of cheese or 200 K> of butter would be obtainable. Dairy Treatment. Cows are commonly milked by hand two or three times a day. A milking machine of American origin, which was introduced about the year 1862, has been entirely abandoned. The milk should be drawn from the animals in as clean a condition as possible, but notwith standing every precaution some amount of hair and epithelial and other animal debris invariably enters the milk-pail. It has therefore to be immediately strained through a sieve with fine wire-cloth or hair strainer. As milk is peculiarly susceptible of taint, and absorbs odours of all kinds with great avidity, it is of the utmost con sequence that all vessels in which it is placed or kept should be so made as to be easily purified and that they should be kept scrupulously clean. In Switzerland milk is strained with most beneficial effect through sprigs of washed fir tops, which inserted loosely and uprightly into the hole of a funnel arrest all hair, skin, clots, and slimy matter on the acicular leaves. The milk drains through in a clean condition with a fresh slightly aromatized flavour favourable to its keeping. A fresh sprig is used on each occasion of straining milk, so that there is freedom from the risk of taint which arises through the use of imperfectly cleaned wire gauze. The milk must be removed from the cow-house as quickly as possible ; and, if intended for use as new milk and for sale in the neighbourhood of the dairy, it may at once be put up for delivery. But if it has to travel a distance, or if it is to be kept for creaming or cheese-making, it should be rapidly cooled down, and kept in a cool airy milk-room if prac ticable, surrounded with fresh cold water. The ordinary method of separating cream either for direct use or for butter making is by allowing it to form on the surface and skimming it off with a broad flat spoon ; but ingenious adaptations of centrifugal machines of which Laval s separator is one of the best known have been introduced for the purpose of effecting the rapid and complete separation of the cream. The centrifugal force of such machines throws the denser portions of the fluid towards the sides of a rapidly revolving cylinder, collecting the cream on an inner layer, which is carried off by one channel while the impoverished milk escapes by another. The Laval separator gives very rich cream, as will be seen from the following analyses by Voelcker : Relative Composition of Milk and its Products. Water. Fat. Casein. Albumin. Milk Sugar. Ash. Whole milk 87-60 77-30 90-34 14-89 91-00 59-30 94-00 3-98 15-45 1-00 82-02 0-80 6-43 0-35 3-02 3-20 2-87 1-97 3-50 24-22 0-40 0-40 0-20 0-45 0-28 0-20 3-53 0-40 4-30 3-15 4-63 0-28 3-80 5-01 4-55 0-70 070 0-71 0-56 0-70 1-51 0-60 Cream Skim-milk Butter.. . ... Buttermilk Curd Whey ... Ordinary Cream. Cream by Separator. Skimmed Milk by Laval Separator. Ordinary Skimmed Milk. Water 77-30 66-12 90-82 89-25 Butter fat 15-45 27-69 31 1-12 Casein 3 40 2 69 3 31 3-69 Milk sugar 3-15 3-03 477 5-16 Mineral matter 0-70 0-47 0-79 078 After being kept some time, depending principally on the temperature at which it is maintained, milk begins to turn sour owing to the formation of lactic acid, by a process of fermentation, at the expense of the lactose or milk sugar. The acid so developed causes a coagulation of the casein, and the milk separates into a solid white curd, and a thin transparent yellow milk serum or whey. These changes can to a certain extent be artificially pro duced, hindered, and controlled. The following are the results of analyses by Fleischmann : Constituents of 100 Parts of Sweet Milk. 3-56 butter. 20-00 cream 16 30 buttermilk. 0-14 loss. 7-93 curd. 79 70 skimmed milk 71 "45 whey. ( 0-32 loss. 0-30 loss.... 0-30 loss. The simplest and most advantageous form in which milk can be disposed of as a commercial product is by its sale as sweet or new milk, and it is in this manner that the greater proportion of the milk produced within the reach of large centres of population is disposed of. New milk, cream, and skimmed milk are the only primary forms in which milk is sent into the market. CHEESE and BUTTER, have been dealt with in separate articles (q.v.). Whey, the yellow liquid remaining after the separation of the curd in cheese making, is a source of milk sugar, employed to a limited extent in pharmacy ; but it is prin cipally used for feeding pigs. The buttermilk which re mains after separating butter is a most wholesome and nutritious article of food. Preservation of Milk. The numerous methods which have been proposed for the preservation of milk in a condition fit for use over a lengthened period resolve themselves into (1) chemical treatment with alkaline salts and antiseptic bodies, (2) physical treatment, such as cooling or icing, boiling, and aeration, and (3) condensation with or without the addition of a preservative agent. All systems of preservation, however, are subject to serious disadvantages either from their serving their purpose for too limited a time, or their interfering with the natural constitution and properties of the milk. Of all preservatives cold is the most efficient and least objectionable. It has been shown by Soxhlet (Dinglcr s Polytech. Journal, ccxxiii. 329) that milk cooled by ice-water remains sweet and unaltered for fourteen days, but after that time acquires a rancid taste. After twenty-eight days it coagulates on boiling owing to the presence of acids resulting from the oxidation of the cream, and in thirty-four days it coagulates even in the ice-water. It is also found that milk which has undergone aeration with atmospheric air has its keeping properties much improved. The aeration is effected by allowing the milk to fall from some height in a state of fine division by passing it through the meshes of a sieve. By another method air cooled by passing over ice is blown through the milk. Milk keeps sweet for a longer time when boiled, but the smell, taste, and other properties are affected, partly owing to the escape of gases mixed with it when fresh. The unpleasant flavour com municated by boiling can be avoided if the action takes place in a closed vessel and the milk is immediately cooled down in a refrigerator connected therewith. In the case of any suspicion of taint in milk either from disease in the cow, contamination from unhealthy persons, or the use of infected water in cleaning vessels, boiling is also strongly to be recommended, as it effectually destroys the germs of disease, in the carrying and spreading of which milk is a most active agent. It is with the utmost difficulty that boiled milk can be coagulated by means of rennet ; but by- treatment with acid it coagulates more rapidly and freely than if unboiled. Of the various chemical compounds which have been suggested and more or less used for preserving milk, the most successful hitherto has been salicylic acid, which has the advantage of being tasteless and inodorous. By briskly stirring in rather less than 2 grains to a pint of milk, it can be kept liquid and sweet in a tem perature of from 65 to 68 Fahr. for twelve hours, and at 55 Fahr. for a whole day. If 4 grains be used to a pint, coagulation in the higher temperature is delayed from two or three days, and at the lower temperature the milk may be kept good from three to five days. Boracic acid and borax are also employed by dairymen, the former being known as glacialine salt. The presence of any chemical anti septic in milk is, however, at best a matter of doubtful advantage. Condensation. Milk is now treated on a large scale by a process of concentration, the product of which comes into the market in two forms as " plain condensed milk " and as " preserved milk." The credit of originating the industry is due to Mr Gail Borden of White Plains, New Yore, who began his experiments about 1849. In 1851 he introduced his plain condensed milk, which is simply milk from which between three-fourths and four-fifths of the water has been removed, and in 1861 he rendered important services to

the army in the field by supplying preserved milk which was in