METABOLIC PRODUCTS 277 



presence of some air, especially at the start. This allows some increase 

 in the number of cells and reduces the amount of inoculum required. The 

 amount of oxygen available to submerged mycelium or cells, unless 

 vigorous aeration is used, is insufficient to inhibit alcoholic fermentation 

 by certain species. 



Alcoholic fermentation has been studied since the time of Lavoisier. 

 Few fields of study have been so valuable in increasing our understanding 

 of the life processes of microorganisms. Harden (1932) has concisely 

 reviewed the early work and theories on fermentation. The idea that 

 yeasts as living fungi were the proximate cause of fermentation did not 

 gain acceptance for many decades. The eminent Wohler (1839) ridiculed 

 this idea in a lively skit, in which he declared that he had followed the 

 entire process microscopically. Briefly, he states that the responsible 

 organism developed from an egg and had the shape of a Beindorf distilling 

 flask; "... diese Infusorien fressen Zucker, entleeren aus dem Darm- 

 kanal Weingeist, und aus den Harnorganen, Kohlensaure." 



The enzymatic nature of alcohol fermentation was established by 

 Buchner (1897). The enzymatic transformations involved in fermenta- 

 tion were discussed in Chap. 7. Further information and references may 

 be found in Summer and Somers (1947), Tauber (1949), Prescott and 

 Dunn (1949), Meyerhof (1944, 1949), Nord and Mull (1945), and Foster 

 (1949). 



The larger part of the world-wide fermentation industry is devoted 

 to the production of ethyl alcohol. During the war year of 1945 some 

 600 million gallons of 95 per cent ethyl alcohol was produced in the United 

 States alone. Less than one-third this amount was produced in 1948. 

 Of this amount 64 per cent was produced by fermentation (Lee, 1949). 

 While any source of fermentable sugars may be used for the production 

 of alcohol, the more common raw materials include molasses, starch from 

 various sources, hydrolyzed cellulose or wood sugar, and fruit juices. It 

 is beyond the scope of this text to discuss the commercial production of 

 industrial and beverage alcohol. For information on these subjects see 

 Prescott and Dunn (1949). 



ORGANIC ACIDS 



Many fungi synthesize organic acids, which accumulate in the medium. 

 These acids include oxalic, citric, succinic, fumaric, malic, lactic, itaconic, 

 kojic, gluconic, and others. Commonly, a species may synthesize a 

 variety of related acids. The isolates of a given species may differ widely 

 in synthetic capacity. To obtain maximum yields, it is necessary to 

 control nutritional and environmental factors closely. The optimum 

 conditions for one isolate may differ from those of another isolate of the 



