52 PRACTICAL DAIRY BACTERIOLOGY 



action of the yeast upon the modified milk sugar. The beverage 

 that is produced contains alcohol, lactic acid, and certain other 

 flavors, which are produced by the bacteria action on the milk. 

 Other types of fermented milk beverages are found in va- 

 rious countries. One called leben * is common in Egypt. Mazun " 

 is made in abundance in America. The Turkish people have 

 one which they call yoghourt. 3 In Sardinia an alcoholic milk 

 beverage is called goiddu* In all of these cases the bever- 

 age is made by ferments which the people prepare by special 

 methods and keep on hand. In many places the ferment is 

 simply a little of the old fermented milk inoculated into the 

 new milk. Most of these forms of alcoholic milk have been 

 studied by bacteriologists and have been found to be based, in 

 general, upon the same principle. They all represent a combined 

 action of bacteria and yeasts. The bacteria, in all cases prob- 

 ably* first change the nature of the milk sugar, so that it is 

 fermentable, and the yeast subsequently changes the sugar into 

 alcohol and carbon dioxide. These beverages are frequently 

 regarded as more easily digestible than ordinary milk, and they 

 certainly have a more pleasant flavor. Perhaps their popularity 

 is due simply to the fact that they contain alcohol. 



FERMENTATION CHANGING THE COLOR OF MILK 



The first type of fermentation ever studied in milk was blue 

 milk which, even 60 years ago, was found to be a more or 

 less common dairy trouble in certain sections of Europe. The 

 phenomenon appears as follows: 



The milk is perfectly normal when drawn, and for several 

 hours afterward, but at about a time when it begins to become 

 sour, blue spots appear in it, which extend through the milk 



1 Rist and Khoury. Ann. d. 1'Inst. Past., xvi., p. 65, 1902. 

 * Duggeli. Cent. f. Bact., II., xv., p. 577, 1905. 

 3 Zeit. f. Fleisch u. Milch Hyg., xv., p. 248, 1905. 

 ' Grisconi. Milch. Zent., II., p. 425, 1906. 



