Chapter IV 



The Applications of the Lactic Acid 

 Fermentation in the Dairy Industry 



IN Northern and Central Europe " long " and " thick " milks 

 are prepared in the household as articles of diet ; in Southern 

 Europe and the neighbouring regions of Asia and Africa, other 

 forms of sour milk are prepared which generally also develop a more 

 or less vigorous alcoholic fermentation. These milk products, 

 which are all credited with great dietetic value, appear under 

 different names in each country without necessarily being different 

 in nature. Thus, the author found the same organisms in the 

 Sardinian Gioddu as in the Bulgarian Yoghurt, while Kefir grains 

 have been found to vary in composition to such an extent that all 

 that they could be said to have in common was their peculiar 

 structure. All these products are of considerable bacteriological 

 interest, as in many cases they contain different organisms which 

 mutually benefit one another, forming genuine illustrations of 

 symbiosis. They may be classed in two groups according to the 

 completeness of the symbiosis. To the first group belong Mazun 

 (Armenia) and Yoghurt (Bulgaria), and to the second group, 

 Leben (Egypt), Kumys (Russian Steppes) and Kefir (Caucasus). 



The products of the first group contain both true lactic acid 

 bacteria and lactose-fermenting Saccharomycetes. The latter 

 contribute to the aroma, but otherwise play a minor part. The 

 principal organisms are rapidly growing lactic acid streptococci 

 and strongly acidifying rod forms. The former are less anaerobic 

 than the latter and prepare the way for them. The rod form of 

 Mazun produces dextro lactic acid, while that of Yoghurt, Thermo- 

 bacterium bulgaricum, produces the Isevo acid. In addition to 

 the last -mentioned organism, another rod form may occur in 

 Yoghurt ; this forms feathery colonies in agar tubes and pro- 

 duces inactive lactic acid ; the author has named it Thermo - 

 bacterium Jugurt. Good Yoghurt * may be prepared by boiling 

 or pasteurising good milk, cooling to 50 C., inoculating with the 

 proper organisms (the yeast may be dispensed with), bottling 

 and keeping at 40 C. At higher temperatures the rods will pre- 

 dominate, while at lower temperatures these will be displaced by 



1 This name is derived from the Turkish "Jugurt." 



