CHAPTER XXXVIII. 



THE OXYDASES. 



214. The Browning of Wines. 



IN addition to the purely chemical absorption or fixation of 

 oxygen (e.g. in the conversion of S0 2 into S0 3 ), on the one hand, 

 and the oxidation effected directly by the vital activity of micro- 

 organisms on the other, there is a third method of transferring 

 this gas, viz., by the action of enzymes, to which the name 

 oxydases, proposed for them by Weigert, may be generally applied. 

 How many kinds of oxydases exist is a matter for future research 

 to determine. At the present time the subject is merely in an 

 incipient stage, though the commencement made is a highly pro- 

 mising one, and has already led to the explanation of several 

 phenomena which only a short time back were regarded as ex- 

 tremely puzzling. 



One of these is the so-called " browning " of wines, known in 

 France as "la easse," " le cassage" or " cassure " (Ger. Ralin-Werden 

 or Braumverden). This occurs chiefly in white wines, and was 

 for a long time classed along with the malady known as loss 

 of colour in (red) wines. In France attention was first directed 

 to its distinct character by AEM. GAUTIER (I.) in 1878, but in 

 Germany this was known at an earlier date. The most important 

 characteristic of " vin casse " is the rapid change of colour under- 

 gone by the wine as soon as it is poured out of the cask or bottle 

 into an open glass, the colour of the upper layers (exposed to the 

 air) of the hitherto pale liquid becoming darker, and finally (in 

 the course of a few hours) becoming brown. This coloration also 

 gradually progresses in the deeper layers, and, at the same time, 

 the flavour becomes unpleasant (air taste). Turbidity then ensues, 

 but disappears in proportion as a fine dark brown pulverulent 

 sediment settles down. The liquid is now (three to four hours 

 after the commencement of the experiment) again bright, though 

 darker in shade than when newly drawn from the cask. The 

 taste has also improved again, without, however, being equal to 

 what it was at first. 



In view of the fact (indubitably proved by Nessler's experi- 

 ments) that this malady only occurs when air is admitted, it was 

 regarded as an oxidation process, without any more precise accept- 

 able explanation being forthcoming. After Gautier had presumed, 



