288 VINOUS FERMENTATION. 



is obtained when the mash is made quite neutral by 

 means of ashes or carbonate of lime, but that the 

 proportion of oil in the brandy is also increased. 



Now it is known that brandy made from potato 

 starch, which has been converted into sugar by 

 dilute sulphuric acid, is completely free from the 

 potato oil, so that this substance must be gene- 

 rated in consequence of a change suffered by the 

 cellular tissue of the potatoes during their fermen- 

 tation. 



Experience has shown that the simultaneous 

 fermentation or putrefaction of the cellular tissue, 

 by which this oil is generated, may be completely 

 prevented in the fabrication of brandy from corn.* 



The same malt, which in the preparation of 

 brandy yields a fluid containing the oil of which 

 we are speaking, affords in the formation of beer 

 a spirituous liquor, in which no trace of that 

 oil can be detected. The principal difference in the 

 preparation of the two liquids is, that in the fermen- 

 tation of wort, an aromatic substance (hops) is 

 added, and it is certain that its presence modifies 

 the transformations which take place. Now it is 

 known, that the volatile oil of mustard, and the 

 empyreumatic oils, arrest completely the action of 

 yeast ; and although the oil of hops does not possess 



* In the manufactory of M. Dubrunfaut, so considerable a quantity 

 of this oil is obtained under certain circumstances from brandy made 

 from potatoes, that it might be employed for the purpose of illumina- 

 ting his whole manufactory. 



