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 SO., 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 promising one, and has already led to the explanation of 

 several phenomena which only a short time back were regarded as extremely 

 puzzling. 



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

 " la casse" "le cassage," or "cassure" (Ger. Rahn-Werden or Braunwerderi). 

 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 ARM. 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 undergone 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 pro- 

 gresses 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 experiments) that 

 this malady only occurs when air is admitted, it was regarded as an oxida- 

 tion process, without any more precise acceptable explanation being forthcoming. 

 After Gautier had presumed, and A. BOUFFARD (I.) in 1894 had denied, the 

 probability of bacterial activity in this phenomenon, it was shown by G. 

 GOUIKAND (I.) that we have here to do with the action of an enzyme which plays 

 the part of a carrier of oxygen. He isolated the same (though not in a pure 

 state) from browned (white and red) wines, and produced therewith the same 

 malady in previously sterilised sound wines. This enzyme must probably be re- 

 garded as acting by the absorption of atmospheric oxygen, which it then gives up 

 again, not only to the colouring-matter in the wine, but also to the tannin, and 

 thus converting them into insoluble dark-coloured compounds. It is to be hoped 

 that, ere long, this matter will have been made clear by further investigation. 



It is found by experience that the wines obtained in wet autumns from 

 rotten grapes, as also those affected with " sweet-rot " (Edelfdule ; pourriture 

 noble), and such as are poor in acid, are subject to this malady with comparative 



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