216 , MICRO-ORGANISMS AND FERMENTATION. 



ENGEL considered this organism to be the most active agent 

 in the fermentation of bread. 1 



1 Decisive experiments on the essential active factors in the fermentation of 

 bread have not yet been made. In making white bread, " pressed -yeast " is 

 ordinarily used ; this consists mainly of alcoholic ferments, and yeast is the 

 only active ferment. In the preparation of black bread, and in some countries 

 also of white bread, so-called leaven is employed ; this is made by kneading 

 together flour, bran, and water, and allowing the mass to undergo spontaneous 

 fermentation. It contains bacteria in large numbers, and also yeast-like cells, 

 and amongst the latter alcoholic ferments. Antagonistic views have, however, 

 been expressed respecting the relative importance of these different organisms 

 in the fermentation of black bread. 



According to CHICANDART (1883) and MARCANO the active ferment is a 

 bacterium. BOUTROUX attributed the fermentation to the activity of both 

 bacteria and budding fungi ; he afterwards regarded alcoholic yeast as the 

 chief cause. LAURENT regarded the so-called Bacillus paniftcans as the main 

 cause of the fermentation of bread. DUENNENBERGER'S investigations led to the 

 conclusion that the budding fungi must be looked upon as the only essential 

 organisms of fermentation in bread. The rising of dough is caused in the first 

 place by the carbon dioxide liberated during the alcoholic fermentation ; 

 further by the expansion of air and the volatilisation of alcohol, water, and 

 fatty acids formed by the bacteria. PETERS found four different budding 

 fungi in leaven, and one of these has been identified with Saccharomyces minor 

 (ENGEL). The second is of about the same size as Saccharomyces minor ; the 

 cells are egg-shaped, and in nutrient liquids develop to moderately large 

 colonies with many branches ; it yields spores abundantly. In addition to the 

 above, a species of Mycoderma and a species related to Saccharomyces cerevisia* 

 were also found. PETERS describes several species of bacteria occurring in 

 leaven, but none of them exhibits all the properties of LAURENT'S Bacillus 

 panificans ; these properties appear, indeed, to require distribution among 

 various bacteria. LAURENT was probably, therefore, dealing with impure 

 cultivations. These bacteria give no alcoholic fermentation, and no appreciable 

 evolution of gas in sterilised dough. 



LEHMANN has recently found, during his researches on leaven, that a single 

 species of bacterium predominates, which he calls Bacillus levans. This 

 bacterium forms lactic and acetic acids in sugar-broth, while carbon dioxide 

 and hydrogen are disengaged ; it is able to ferment sterilised flour. In certain 

 ways this bacterium appears analogous to Bacillus coli communis. LEHMANN 

 assumes that the yeast present in leaven is also active in the process. 



The above experiments constitute a good preliminary to the decisive experi- 

 ments on the cause and action of the rising of dough. 



The diseases of black bread which have been investigated by UFFELMANN, 

 KRETSCHMER, and NIEMITOWICZ, (e.g., vigorous growth of mould, sliminess 

 caused by an exuberant growth of bacteria), may no doubt be partly attributed 

 to impure leaven, in which the most varied organisms will thrive. 



