DAIRY FARMING— DA.TBYING. 289 



the natural process of vegetative division is hastened by the mechanical action, bo 

 that bacteria about to become separated are torn apart sooner than would ordinarily 



occur. 



On the effect of heat on cow's milk, < ). Jensen and E. Plattneb (Ann. Agr. 

 Wuisge, 6(1905), No. 6, pp. 905 988; Rev. Gin. Lait, ', (1906), Nos. 16, pp. S61 

 /;, pp. 888-897; 18, pp. U9-484). — Samples of mixed milk were heated momentarily 

 or for periods of 5, b~>, •".<>. or 60 minutes, or 5 hours, at temperatures ranging from 

 BO to 140° ('.. and subjected to chemical examination. 



The albumin was partly coagulated at 60° when the heating was prolonged for 5 

 hours, though the greater pari was not precipitated below a temperature of 70 75 . 

 Ill the albumin was coagulated by heating at 77.5° for 1 hour. 80 for ■' hour, or 90 

 |»r 5 minutes. Momentary boiling, provided the milk was brought rapidly to the 

 boiling point and promptly cooled, left traces of albumin in solution. 



The casein was coagulated by heating for 30 minutes at 130° or for 5 minutes at 

 140°. By heating at the latter temperature for 30 minutes a fourth of the casein was 

 transformed into soluble oitrogenous substances nonprecipitable by acetic arid. 

 Changes in the casein, however, occurred at lower temperatures and contributed in 

 producing the browning usually ascribed solely to a caramelization of the lactose. 



The degree of acidity was at first reduced by heating on account of the expulsion 

 ■ carbon dioxid, but at higtier temperatures it was increased, which was believed to 

 he due to the decomposition of the casein and the formation of acids rather than to 

 changes in the lactose. The cooked taste was believed to be closely associated with 

 the changes produced in the albumin. 



Btorch's paraphenylenediamin test gave negative results when applied to milk 

 heated momentarily at 80°, 5 minutes at 75°, 30 minutes at 72.5°, or 5 hours at 70 . 

 The total destruction of the superoxydase, upon which this test depends, occurred, 

 perefore, sooner than the complete coagulation of the albumin. In general Storch's 

 reaction ceased precisely at the point where the cooked taste manifested itself. 



Heating increased the time required for the coagulation of milk by rennet grad- 

 ually up to the point of minimum acidity, at which stage the time required forcoag- 

 ulation increased very abruptly and then remained constant until the heating was 

 sufficient to cause a browning of the casein, when a further marked increase in the 

 time of coagulation was observed. The first of these two critical stages was reached 

 hy momentary boiling or by heating for 5 minutes at 80°, 1 hour at 77.5°, or5 hours 

 at 70°, and the second by heating for 5 minutes at IL'0 or 30 minutes at 110°. 



To determine the cause of this delayed coagulation the ant hois added milk enzyme 

 in the form of separator slime and also lactalhuinin to heated milk without affecting 

 ft any marked extent the time required for coagulation. The main alterations in 

 kated milk affecting its coagulation with rennet and o.ccurring at the two stages 

 mentioned are, therefore, believed to be due to changes in the casein molecule. The 

 minor changes as regards coagulation brought about previous to the first critical stage 



fee considered as due to the expulsion of carbon dioxid and probably also to the 

 destruction of natural rennet in the milk and in some cases to the precipitation of 

 lime salts. 



The lactose as determined polarimetrically showed a marked reduction as a result 

 of heating above 120°. Gravimetric determinations, however, did uot show this 

 reduction. The fat globules showed fusion only when the milk was heated above 

 120 for short intervals or at 70° for 5 hours. 



From the above and other results obtained in these investigations, the authors 



conclude that in order to preserve the properties of raw milk, which is especially 



desirable in infant feeding, the heating should not be continued for several hours at 



P° nor exceed for a single instant 70°. The temperature should not exceed that 



iry for destroying pathogenic bacteria, more particularly the tubercle bacillus, 



