444 MICE.OBIOLOGY OP MILK AND MILK PRODUCTS 



to determine which were necessary for the proper fermentation of 

 the kefir. He found the kefir contained four different organisms: 

 yeasts, streptococci, micrococci, and bacilli. The yeasts and strepto- 

 cocci were plated in gelatin without diflSiculty but it was very difficult 

 to grow the other two organisms present on any artificial media. 

 He concluded that the yeasts present in kefir are not identical with 

 the species commonly used in making beer and named it Sacckar- 

 omyces kefir. The streptococcus curdled milk in less than forty-eight 

 hours at a temperature of 37° but the micrococcus did not curdle 

 milk at all, although it produced a considerable amount of acid. 



De Freudenreich changed the name of the bacillus from Dispora caucasica, 

 giveait by Kern, to B. caucasicus, because it did not produce spores as Kein sup- 

 posed. He also found that this organism would not grow at all on media without 

 sugar, very slightly on milk, serum, agar, and best of all in milk, in which it produces 

 both gas and acid without curdling the milk. This organism is SM or 6jti in length 

 by i/i in width, is slightly motile and retains Gram's stain. It has a thermal death- 

 point of SS° for five minutes. 



The preparation of good kefir seems to depend upon the combined 

 action of the four types of organisms described. Kefir is sometimes 

 prepared without the use of the kefir grains* by placing milk in bottles 

 to which is added a small amount of compressed yeast and sucrose. 

 The bottles are then held at a temperature of 10° to 15° about fifteen 

 hours and shaken occasionally. Kefir prepared in this way gives an 

 effervescent mild flavored drink. 



Leben. — For centuries the Egyptians have used a fermented milk 

 drink known as leben or leben raib. This was prepared from the milk 

 of cows, buffaloes, and goats. In general it resembles the other fer- 

 mented milk drinks in the fact that the fermentation is produced 

 by yeasts and a variety of other microorganisms working together. 

 At least one yeast and three species of bacteria seem to be normal 

 to this product. A fermented milk drink very similar to leben is 

 also used in Algeria. Just the action of each microorganism concerned 

 in the fermentation of this product is not certain, but it is probable 

 that all of the species are essential for the production of the particular 

 flavor and consistency of the fermented product. It is claimed that 

 the fermentation that takes place in the milk renders it more digest- 

 ible than raw milk. For this reason it is recommended for the use 

 of invalids and persons having weak digestion. 



* Milch Zeitung, 1888, p. 393. 



