DISCOLORATION OF VEGETABLE JUICES 309 



frequency. Nessler made searching investigations into the means of combating 

 this complaint in practical viticulture. The most important result obtained 

 was the discovery that the browning of wine can be prevented by thoroughly 

 fumigating the casks with 1-2 grams of sulphur per hectolitre 22 galls, or 

 3.53 cubic feet of cask-room before use, the malady being found, in Nessler's 

 experiments, not to ensue when the wine contained a minimum quantity of 

 0.003 per mil. of S0 2 . According to the researches of Gouirand, this enzyme is 

 destroyed by a temperature of 80 C., 60 C. being apparently insufficiently 

 reliable for this purpose. MULLER-THURGAU (VI.) made the discovery, im- 

 portant in cellar management, that the tendency of wine to turn brown could 

 be prevented by Pasteurisation, i.e. keeping it for some time at a temperature 

 of 6o-62 C., which it will endure without acquiring the so-called " boiled " 

 taste. 



The acquisition of a more accurate characterisation of the enzyme, and the 

 consequent possibility of distinguishing it from other oxydases, is desirable, this 

 being a necessary preliminary to the elucidation of its origin. Possibly the 

 enzyme is not formed anterior to fermentation, but, on the other hand, its 

 presence in the grapes themselves and in the must is not absolutely precluded. 

 V. MARTINAND (I.) has actually found oxidising enzymes in wine-must on many 

 occasions. The elucidation of the conditions under which browning may be 

 caused in wines is a subject requiring further investigation, the question 

 whether the presence of special metabolic products is essential, or whether the 

 oxydase here concerned differs from those observed by Martinand, being still 

 unsolved. Moreover, it appears from the discoveries of this observer that, in 

 the maturing of wine', the alterations of flavour occurring and which may be 

 accelerated by the influence of oxidising agents (ozone, the electric current) 

 are, under natural conditions, brought about by the agency of oxydases which 

 still require closer identification. The same applies to the darkening of the 

 colour of wine during storage. According to G. TOLOMEI (V.), oxydases are 

 also produced by the wine-yeasts Saccharomyces apwidatus and Sacch. ellip- 

 soideiw. 



215. The Rapid Discoloration of Fresh Vegetable Juices 



is in many cases attributable to the action of oxydases. Technical interest 

 in the discoveries made on this point is chiefly centred in the researches of 

 G. BERTKAND (II.) on Japanese lacquer, that lustrous and extremely durable 

 varnish employed in Eastern Asia for coating wooden furniture and similar 

 articles. By making incisions in the bark of the indigenous Rhus vernicifera a 

 tree of the family Anacardiacece and closely allied to the European garden-tree 

 Rhus cotinus (Venice sumach) a juice is obtained which, on admixture with the 

 oil from Bignonia tomentosa and (for red lacquer) vermilion, yields the lacquer 

 in question. This juice resembles a thick pale cream and will keep unchanged 

 for a long time if stored in closed bottles, but quickly turns brown when air is 

 admitted, becoming covered in a few minutes with a tough black skin, and 

 finally hardening this being, in fact, the property for which it is so highly 

 prized. That a process of oxidation is here in question cannot be doubted. 

 The constituent thus converted has been isolated by Bertrand under the name 

 of laccol, and recognised as a compound allied to the polyatomic phenols, and 

 capable of producing extremely violent reddening and inflammation of the skin 

 if applied in even very minute quantities. The juice also contains an oxydase, 

 named by Bertrand laccase, by the known oxygen-carrying powers of which the 

 laccol is rapidly converted into a hard, black oxy-compound, insoluble in water, 

 alcohol, &c. This product is not obtained in the absence of the enzyme, only a 

 resinous soluble grease, that remains sticky for a long time, being obtained under 



