84 PHYSIOLOGY OF YEASTS 



Prevalence of Alcoholic Fermentation 



The phenomenon of alcoholic fermentation is not limited to the 

 yeasts. Many of the molds l are also able to ferment the sugars. 

 But this fermentation is less active and is more prolonged. Further- 

 more, it is only produced under certain conditions. A few examples 

 taken from DuClaux will be given. 



Among the molds, it is known that Sterigmatocystis nigra, which is 

 exclusively aerobic, never produces alcoholic fermentation. Some of 

 the other species, such as Aspergillus glaucus and Penicillium glau- 

 cum, are able to cause a slight fermentation. If, for example, some 

 of the conidia of Penicillium glaucum are inoculated into a Pasteur 

 flask containing a sugar medium, a well-developed mycelium is pro- 

 duced on the surface; after a time, the air becomes reduced in con- 

 centration and carbon dioxide accumulates with traces of alcohol. 

 The amount of alcohol will always remain very small, and will scarcely 

 pass from 1000th to 1500th of the total volume. Under the same 

 conditions, Aspergillus glaucum will produce large amounts of alcohol. 

 Pasteur has shown that in a culture of Aspergillus glaucum cultivated 

 in 122 c.c. of beer wort for a year, 4.4 c.c. of alcohol were produced 

 by a weight of yeast which scarcely surpassed 0.5 gram in the dry 

 state. About seven times the weight of the plant in alcohol were 

 produced. 



Many other molds possess a fermenting action. Mucor racemosus 

 will produce under the same conditions more alcohol than the two 

 fungi mentioned above. According to Pasteur,* the weight of alcohol 

 will be 10 or 20 times the weight of the mycelium. Mucor mucedo, cir- 

 cinelloides and erectus, Amylomyces rouxii and Aspergillus oryzae 

 are in the same category. With the molds, however, fermentation 

 requires a longer time than the yeasts require to ferment the same 

 amount of sugar. 



Comparison of Intramolecular Respiration with 

 Alcoholic Fermentation 



As Pasteur has pointed out, alcoholic fermentation is not limited 

 to the molds nor to the yeasts, but is carried on in all living cells 

 which contain sugar. Indeed, alcoholic fermentation ought to be 

 compared to what is called " intramolecular respiration." 



Berard demonstrated, for the first time in 1821, that fruits which 

 were exposed to the sun absorbed oxygen and liberated carbon dioxide; 



4 Certain bacteria are also known which produce alcoholic fermentation. 



