APPLICATIONS OF LACTIC ACID FERMENTATION 105 



grains ; they confer on the Kefir its slimy consistency and bring 

 about the peptonisation of the casein, besides contributing 

 towards the production of alcohol. In Kefir made from these 

 grains, various streptococci always appear, which contribute 

 towards the production of acid, but for 'the most part they appear 

 to be casual guests. According to Freudenreich, who was one of 

 the first investigators of the Kefir fermentation 1 , certain special 

 strains of streptococci play a part in this process. The grains 

 investigated by Freudenreich appear to occupy an intermediate 

 position between the two varieties described above. 



The preparation of Kefir from the dried grains of commerce 

 requires a somewhat lengthy process of revival. The grains must 

 first be soaked in lukewarm water and then in lukewarm milk 

 which is constantly to be changed before it coagulates. This 

 treatment must be continued till the grains produce sufficient gas 

 to make them rise in the liquid, which may take a whole week. 

 The grains which float are then added to milk in the proportion 

 of 2 to 3 kilos per 10 litres. If there is not a large proportion of 

 grains to milk, the bacteria of the milk itself may easily come to 

 predominate. Under favourable conditions, the weight of the 

 grains will increase by over 40 per cent, in fourteen days. The 

 milk is kept at 20 to 25 C., and frequently stirred or shaken. 

 When active fermentation has set in, the grains are strained off 

 and may, after washing with clean water, be used for a fresh 

 batch ; the milk is bottled, closed up with spring stoppers and 

 kept for one or two days at 15 to 20 C. ; at higher temperatures 

 the bottles may easily burst. The precipitated casein is distri- 

 buted by careful shaking, and the resulting product is an 

 effervescent, somewhat thick fluid containing about 1 to 1J per 

 cent, of acid, and about 0-25 per cent, of alcohol. On longer 

 standing the taste becomes less pleasant owing to the progress of 

 alcoholic fermentation ; in the course of six days, the alcohol 

 content may increase to over 1 per cent. Kefir is undoubtedly 

 of greater dietetic value than Yoghurt, for the author has found 

 that on the drinking of Kefir, the proportion of Gram -positive rod 

 bacteria rapidly increases in the faeces, while the yeast is com- 

 pletely digested, the faeces showing only the empty cell walls. 

 As extract of yeast counteracts certain illnesses, the healing 

 properties of Kefir must be ascribed to the yeast. The author 

 has found that yeast extract promotes the development of the 

 lactic acid rods, but inhibits the development of streptococci, 

 especially the pathogenic species. For people who have com- 

 paratively little hydrochloric acid in the stomach, Kefir, like 



1 " Landwirtschaftliches Jahrbuch der Schweiz," 1896, p.,1. 



