Page:The New International Encyclopædia 1st ed. v. 13.djvu/555

* MILK. 501 MILK. effect ui)on the keeping |)iopprties of butter. Several organisms liave been deseribcd whieli im- part a bitter taste to milk, due, in some cases at least, to the production of a billcr principle, ililk which has been boiled is likely to develop a hitler taste, for the reason that the heating kills the lactie-aeid germs, while the bacteria causing the bitter taste usually possess endo- spores which are not destroyed by heat, and so have a clear field for action. A slimy fermenta- tion of milk is a somewhat common occurrence, and occasionally produces great trouble in dai- ries, since it destroys the milk for all ordinary uses. Such milk becomes thick and ropy, will not cream, cannot be churned, and is unfit for drinking. It may be caused by a variety of or- ganisms. There are several forms of the trouble. One known as the 'lange wei' (long or stringy whey) is made use of in the manufacture of Edam cheese in Holland, to control the gassy fermentation of the curd. In addition to the fermentations and other changes in milk due to micro-organisms, rennet, an unorganized ferment obtained from the stom- ach of the calf and from some plants, ferments milk, causing it to curdle. This ferment is em- [)loyed in cheese-making to produce the curd. Babcock and Russell have discovered an unor- ganized ferment termed galaetase in milk, which they believe to be a normal and inherent con- .stituent, and which is active in the ripening of cheese, causing the characteristic changes in the green cheese which make it suitable for eating. The chief sources of bacteria in milk are the cow herself, the milker, the dust of the stable, and the dairy utensils. It has long been believed that pure milk drawn from a healthy cow con- tains no bacteria, and that all bacterial contami- nation of the milk comes from external sources. However, the large calibre of the milk duct makes it possible for bacteria to enter it and grow to a considerable extent, so that it becomes a matter of extreme difficulty to obtain milk from the cow, even with the greatest precautions, which shall not be contaminated. The hairs of the cow are always covered with dirt and dust, and the air of the stable is charged with dust from the fodder and bedding material, so that it is impossible to lu'event some of this dirt falling into the milk ])ail. Thus large numbers of bacteria, especially in poorly ventilated stables, reach the milk. Any dirt upon the hands or clothing of the milker will have abundant chance to get into the milk ]iails and cans. The milk vessels themselves are an important source of contamination, the cor- ners and creases retaining bacteria which have not been removed or killed by the washing. The warm milk furnishes favorable conditions for the growth of these micro-organisms which have gained access, and which for a time multiply rap- idly. Several species of bacteria classed as patho- genic organisms are capable of living or even in- ercasing in milk, but since they do not ferment the milk or alter its appearance siffieiently to be detected by a physical examination, their presence is not readily determined. Except in very rare instances the milk becomes, contaminated after it has been drawn and in practically all these cases the cause of contamination is some form of un- cleanliness. either of the stables, the water, the utensils, or the attendants. It is gratifying to know, however, that through the efforts of the tnited States l)i|)artnient of Agriculture, the agricultural experiment stations, and the dairy- men ihemselves. llie sanitary management of dairies is being constantly improved, and through the vigilance of State appointed dairy inspectors unsanitary conditions are destroyed as soon as discovered. Milk Adulteration and Control. The milk supply of towns and cities has for many years been regulated by laws and ordinances, and sub- jected to inspection. The object of this was for- merly to prevent adulteration, bu( of recent years the inspection has often extended to the herds and stables and all that relates to the milk trade. It has come to be realized that such fac- tors as the health of the cows, hygienic condi- tion of the stables, and cleanliness in the hand- ling of the milk are quite as es.sential to pure wholesome milk as freedom from adulteration. Hence the veterinary inspection, which has been introduced in some cities, should be extended. Milk is most often tampered with by removing a part of the cream, or by diluting it with water or skim milk. Coloring mailer is sometimes added to make it appear richer, but the addition of chalk, burnt sugar, or similar substances is now rare. Preservatives, such as formaldehyde, borax, and salicylic acid, are sometimes added to prevent milk souring. Opinions differ as to the injuriousness of these preservatives, but their iise is generally condemned on the ground that they are unnecessary in pure milk, and that they are a cloak for unsanitary practices in the dairy. The standards for milk adopted by different States vary from 11. .5 to 13 per cent, for total solids and from 2.5 to 3.5 per cent, for fat. Milk found below these standards is held to be adul- terated. A standard of 12.5 per cent, of total solids and at least 3 per cent, of fat seems fair. Various means of testing milk as to its qual- ity have been suggested from time to time. Of these the lactometer is the simplest, and has been extensively used by milk inspectors who have a large number of samjdes to examine daily, to detect watering or skimming. It is a form of hydrometer, which shows the specific gravity of milk upon a graduated scale. But there are so many factors that aft'ect the specific gravity, and this maj- vary so much in pure milk, that the lactometer reading is only an indi- cation and cannot be relied upon as final. The most reliable and satisfactory of the simple milk tests is the Babcock test, which has come into very widespread use in the milk inspection of towns and cities, and in determining the fat eon- tent of milk as a basis for paying for the prod- uct at creameries. (See Creamery: Butter- Making.) This test is made in a special bottle having a narrow graduated lu'ck. A definite quantity of milk is treated in the bottle with sulphuric acid to dissolve the curd and set the fat free. The bottle is then whirled rap- idly in a centrifugal apparatis for a few min- utes, to aid in separating the fat : hot water is added to bring the fat up into the neck, after which the bottle is whirled a second time and the column of fat read off on the graduated scale. The reading gives the percentage of fat without calculation. -A large number of samples may be tested simultaneously, and the method has been shown to be very accurate after a little practice. It shows onlv the fat content, which is the com-