A GREAT deal has been written during the last few years upon the effects-deleterious or otherwise-of heat upon milk. That certain changes are brought about in the composition of milk by heating seems to be generally agreed, but enquiries into the nature of these changes have generally been made only at one or two particular temperatures. It was felt that possibly results of more value might be obtained by studying the effect of heating milk over a wide range of temperature, and it was decided to investigate the effect of heat upon [a) the time of coagulation by rennet, and (b) the solubility of the calcium, phosphorus and nitrogen present.One of the most fundamental properties of milk is its coagulability by rennet and in the manufacture of cheese the production of a satisfactory curd from the milk on the addition of rennet is one of the most important factors. Upon the nature of the coagulum formed in the early stages of the manufacture of any cheese depends to a great extent the quality of the final product. For the production of a good cheese, it is necessary that a firm coagulum shall be produced by the addition of a definite quantity of rennet to a known volume of milk at a standard temperature. If for any reason, coagulation is delayed, and the resulting coagulum is soft, whey will not drain freely from the curd, and the resulting product will generally be poor both in texture and flavour.In practice it has been found by cheese makers that a soft unsatisfactory curd which is difficult to drain is always produced when the usual quantity of rennet is added to milk which has been pasteurised, but it has also been found that the addition of lime water or a solution of caWium chloride to the milk before the addition of rennet results in
THE following paper gives the results of the first of a series of researches designed to investigate the composition and properties of normal milk.Although it is realised that a complete study of lactation can only be made when physiological technique is available to follow the formation of milk to its natural source, yet the marked differences in reaction which had been observed in studying the pH of individual quarters by the changes in colour produced when the milk was tested with brom cre'sol purple paper, suggested the possibility of similar variations in other properties. It was, therefore, decided to make a comparison of the composition and physical properties of milk as it leaves the individual teats of a healthy cow 1 .When this work was begun the only available records of analysis of milk from individual quarters were those of Ingle (l) and Fitch and Copeland(2). More recently Rice and Markley (3) and Kieferle, Schwaibold and Hackmann(4) have dealt briefly with this subject, but none of these workers made a prolonged study of the question; Ingle stated that he was unacquainted with any published account of previous investigations on the subject. He gave variations in the fat, solids and yield for two cows for six consecutive milkings and for a single milking of a herd of nineteen cows. He stated that "from these inquiries it appears that the left fore quarters of the udders yielded on the average milk containing the least percentage of solids-not-fat, and that as a general rule, to which, however, there are a few exceptions, the quarter of the udder which gives the smallest quantity of milk yields also the milk containing the smallest percentage of solids-not-fat." He concluded by saying that "the variation in fat in milk from different quarters of the udder is perhaps not surprising when we remember that the fat is apparently produced by the breaking down of fat cells in the gland itself; but that different glands or different parts of the same gland should be able to elaborate from the same blood supply products of different concentration in dissolved matter, appears to the writer to be very remarkable. The results should certainly prove of interest to the physiologist though they perhaps have little importance from a dairy point of view." Fitch and Copeland determined the yield and fat content of the individual quarters of five cows for eight milkings, and concluded that "no one quarter
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