I 4 4 



. 



3) Sugars when fermented by yeast normally give ethyl al- 

 cohol and carbon dioxide, but owing to malnutrition of the yeast 

 or some similar cause, acetaldehyde may make its appearence in 

 place of ethyl alcohol to a greater or less extent. 



The first two hypotheses are now out of the question since by 

 the authors' experiments it was shown that yeast will give very 

 varying amounts of acetaldehyde, according to the materials on 

 which it is nourished being altered. Moreover the results obtained 

 by the authors with yeasts from different breweries point to the 

 same conclusion: the production of aldehyde varying at different 

 times with yeast from the same brewery. Any possibility of the 

 aldehyde having been produced by subsequent catalytic oxidation, 

 owing to the presence of small amounts of salts of heavy rnetals, 

 was carefully excluded, by performing all fermenting and distilling 

 operations in glass vessels. 



Evidently, then, the aldehyde must be a product derived from 

 the sugar under the action of the yeast, the cause of the variation 

 in amount being due to the different food the yeast is supplied 

 with during fermentation. 



In order to obtain an idea as to which of the other constituents 

 of the mash could affect the greater or lesser production of alde- 

 hyde, systematic experiments were carried out, solutions being made 

 up, of known composition. Generally, crystallised sucrose or dextrose 

 was employed, togethers with necessary mineral constituents, ni- 

 trogen being also supplied either in the form of ammonium salts 

 or as amino-acids. 



In view of the work of F. Ehrlich (Zeitsch. Ver. deut Zuckerind., 

 1905, 55-539; Biochem. Zeitsch., 1906, /, 8, 2, 52; Ber., 1907, 40, 

 1027) on the production of higher alcohols from the amino-acids 

 with extra carbon atoms, (for example, of ordinary iso-amyl alcohol 

 from leucine) complications were avoided by using alanine as amino- 

 acid, since this can give no other alcohol but ethyl alcohol. In 

 fact, the present authors started the work quite expecting to find 

 that deficiency in available nitrogen would mean increase in al- 

 dehyde content, and it was thought not at all unlikely that the 

 function of amino-acids and their conversion into alcohols during 

 fermentation might be connected with the formation of ethyl al- 

 cohol and carbon dioxide from some intermediate product, possibly 

 lactic acid. These experiments evidently showed that lack of ni- 

 trogenous food is not the cause of aldehyde formation. 



In view of the observations made by E. Drechsel (Ber., 1892, 



