SUGARS SUSCEPTIBLE OF FERMENTATION. 511 



is obtained when the starch has been saccharified by diastase, and 

 distillation has been effected by steam ; so that it is not a product 

 of fermentation. According to W. WINDISCH (IV.), it is produced 

 by boiling acid solutions of carbohydrates, especially the wide- 

 spread pentoses and pentosans, and is therefore formed in the 

 distillation of the invariably slightly acid mashes, wines, and 

 beers. This explains why C. HEIM (I.) found Munich beer to be 

 destitute of furfural. BRAND (II.) and HEIM (I.) failed to obtain 

 confirmation of W. WINDISCH'S (II.) hypothesis that the pasteurisa- 

 tion flavour of beer is due to furfural. It is, however, certain that 

 when beer containing no furfural is boiled for a sufficient time, 

 furfural makes its appearance ; and the same is naturally the 

 case with distillery washes and wine. The test recommended by 

 LENZ (I.), namely, that the occurrence of the furfural affords 

 decisive proof that a sample of cognac is a pure wine distillate, is 

 unreliable. 



K. WINDISCH (III. and IY.) states that fermentation products 

 have also been found to contain terpene and terpene hydrate, as 

 well as oils of high boiling-point, derived from the raw materials. 

 Under certain conditions, sulphur compounds may also occur in 

 the products of industrial fermentations, K. WINDISCH (V.), for 

 instance, having found sulphuretted hydrogen in wine, whilst 

 BARBET (I.) and ELWART (I.) observed sulphurous esters in spirits 

 produced from molasses and sulphured saccharine juices. The 

 formation of these compounds may be readily explained by the 

 reducing action of yeast enzymes in presence of free sulphur or 

 sulphur dioxide. 



326. Sugars Susceptible of Direct Fermentation. 



As already mentioned on p. 484, vol. ii., saccharose will not fer- 

 ment until it has taken up a molecule of water, in which operation 

 it is transformed by the enzyme, invertase (see 327), into two 

 hexoses, glucose and fructose, according to the equation : 



Cia^Ai + H 2 = C 6 H 12 6 + C 6 H 12 6 . 



For a long time this observation was unique of its kind, all 

 attempts made to convert maltose which has the same empirical 

 composition as saccharose into two hexoses by a similar enzymatic 

 decomposition, having failed ; so that it was held that maltose 

 undergoes direct fermentation (compare MOKRIS (III.), HANSEN 

 (LXIY.), DASTRE (I.), DUNNENBERGER (I.), MEHRING (I.), and 

 DONATE (II.)). E. FISCHER (VII.), however, established beyond 

 dispute that maltose is split up into two molecules of glucose by 

 a special enzyme, maltase (see 328), as a preliminary to fermen- 

 tation. His discovery (VIII.), in collaboration with P. LINDNER, 

 that saccharose is also hydrolysed by Monilia Candida (see p. 444, 

 vol ii.), which does not contain ordinary yeast invertase which 



VOL. II : PT. 2 2 K 



