l64 FERMENTATION IN MILK 



mentation, therefore, the milk of the mare is particularly suitable. 

 The chemical changes of the process have been well summarised 

 by Hutchison.^ He states that — 



" The chemical changes which take place in the milk under the 

 double fermentation, are not difficult to follow. The lactic ferment 

 simply changes part of the sugar into lactic acid. The vinous 

 ferment eats up a very small part of the proteid of the milk, and 

 at the same time produces from the sugar a little alcohol and a 

 good deal of carbonic acid gas. The milk thus becomes sour, it 

 effervesces, and is weakly alcoholic. But the lactic acid causes the 

 casein to be precipitated just as it does in the ordinary souring of 

 milk, and the casein falls down in flocculi." 



" Now, one of the essential points in the making of koumiss 

 is that during the whole process of fermentation the milk should 

 be kept constantly agitated by stirring. This agitation is primarily 

 intended to permit of the access of oxygen to the fermenting fluid, 

 but it has also the result of breaking up the precipitated casein into 

 exceedingly fine particles, and it is to this extremely fine state of 

 division in which the casein is found that much of the ease with 

 which koumiss can be digested is to be attributed. As the process 

 goes on, it would appear that a small part, at least, of the casein 

 undergoes a sort of spontaneous digestion, and is converted into 

 soluble products. One certainly finds that ordinary kephir contains 

 a small amount of protone." 



" These changes, of course, only go on gradually, so that at the 

 end of twelve hours of fermentation one gets a weak koumiss which 

 is only slightly sour, and which still looks and tastes quite milky. 

 After twenty-four hours have elapsed some of the casein has been 

 redissolved, with the result that the koumiss is thinner ; it has also 

 increased in sourness. This is called ' medium ' koumiss. After 

 another twenty-four hours or more most of the sugar has been 

 destroyed, and the ' strong ' koumiss which results is a thin, sour 

 fluid which effervesces briskly. In this form it can be kept in- 

 definitely without undergoing much further change." 



" The net change which has taken place in the original milk 

 may be summed up by saying that the sugar has been to a large 

 extent replaced by lactic acid, alcohol, and carbonic acid gas ; the 

 casein has been partly precipitated in a state of very fine division, 

 and partly predigested and dissolved, while the fat and salts have 

 been left much as they were." 



The total proteid in koumiss is hardly less than in mare's and 

 cow's milk, the fat is practically the same as in mare's milk, and 

 the sugar is reduced from about 5 per cent, to 1-5 per cent. The 



* Food and the Principles of Dietetics, by R. Hutchison, M.D., F.R.C.P., 

 1902, p. 136. 



