Fig. 5. The Creamometer a fair idea of its quality. The taste and smell afford some guide, as also the general appearance. To judge of the latter, place some of the milk in a tumbler or other clear glass vessel. If the milk is of good quality it will be quite homogeneous and opaque. Any flocculent matter indicates either disease in the cow or that the milk is old and bacteria have multiplied in it and altered its composition. When the milk has stood long enough for the cream to rise freely, the latter should form a perfectly homogeneous and strongly defined layer on the top. The quantity of cream may be measured in a creamometer, which consists of a small glass cylinder graduated at the top (Fig. 5). It is filled with milk to the top graduation line, and when the cream has risen, the percentage quantity of the latter which has separated can be taken off.
The colour should be like that of porcelain, but, as already stated, it is a common thing for the dairyman to add a small quantity of anatto or an aniline dye of a similar shade, to give the milk a rich creamy tint. If the milk is of a reddish colour this may be caused by blood from the udder, although certain foods, such as beets, mangels, and carrots sometimes give a similar tint. The milk given by cows immediately after calving is called "colostrum" or "biestings," and is of a yellow or yellow-brown colour. It is much thicker than ordinary milk, and coagulates in boiling.
In dirty byres in which care is not taken in milking, quite considerable quantities of hairs, pieces of manure, and other filth may get into the milk. Usually the milk is strained by the dairyman, but sometimes this is omitted or carelessly done. To test for dirt, a ribbed glass funnel is useful. Get a piece of the finest muslin about twice the diameter of the funnel, fold over twice, so that it becomes one quarter of its original size; open one of the sections and place in the funnel; pass the milk into this. It will run through quickly and some water may be run into the funnel to clear away the last traces of milk. The filter cloth can then be opened out and any dirt retained will become visible. The apparatus is shown in Fig. 6.
Testing-Glass for Extraneous Matter in Milk.
Fig. 6.—A piece of muslin is folded as shown and a measured quantity of milk is passed through the funnel; from the sediment left in the muslin, the percentage of extraneous matter may be arrived at.
If a glass funnel is not available, a very small jelly bag can be made of fine gauze and used in the same way. The washing water should be used in small quantities and directed to concentrating the dirt in the apex of the bag. After washing, the latter can be turned outside in, to permit of readier examination of the dirt. The bag should be well washed in cold water, then boiled and dried, and is then ready for future use.
The acidity of milk is a very useful guide to its age. Milk has the curious property of being "amphoteric," i.e., it is both slightly acid and slightly alkaline when fresh. As its age increases, however, so does its acidity, and at a rate varying with the temperature and moisture contents of the atmosphere in which it is placed. Old and acid milk is heavily contaminated with bacteria, a proportion of which are likely to be injurious to health.