The Clarification and Limjpidity of White Wines. 735 



tannin may remain in solution in the presence of albuminous matters 

 in artificial liquids of similar composition to that of wine. If these 

 bodies are associated in proper proportions a liquid that contains a 

 small proportion of them remains limpid, but if a little tannin only is 

 associated with a larger proportion of albuminous matters, the liquid 

 has a more or less pronounced opalescent appearance due to a com- 

 mencement of coagulation of the nitrogenous matters. The precipi- 

 tation of the excess of pseudo-albuminous matters in solution ends, 

 however, by being produced under the influence of a slow coagulation 

 •of which all the causes are as yet not very well known. In this 

 phenomenon, great differences ai-e noticed in accordance with the 

 wines, the districts where they are produced, and the seasons. The 

 ■observations that we have been able to make hitherto have led us to 

 believe that there are two causes which account for these differences. 

 The first is purely physiological. When different varieties of yeast 

 ai'e cultivated in the same must, which has been sterilized but has 

 still kept its opalescent appearance after the fermentation is com- 

 pleted, great differences in the rapidity of the clarification of the 

 wines are noticed. In this clarification it is not only the more or less 

 rapid deposit of the yeast in suspension that must be considered, 

 but also the loss of the original opalescence of the must. These 

 differences appear then due to the variations in the action of the 

 products secreted by the yeasts from the albuminous matters. 

 There are here probably diastasic actions which it would be in- 

 teresting to study closely, since they pertain to the selection of the 

 yeast, and moreover this study should have a practical side. The 

 second cause exists in the action of the oxygen of the air, which 

 may be either exclusively chemical or physiological. Pasteur was 

 the first to unveil the effect of aeration on the colouring matter of 

 wines. During the last few years a more intimate knowledge of 

 the mechanism which rules these effects has been obtained by the 

 discovery of oxidasis, and the phenomenon of " casse" (breaking), 

 incontestably allied to the coagulating actions at the same time as 

 oxidation. Young white wines when exposed to the air are the seat 

 of these phenomena, which take a greater or a lesser intensity ac- 

 cording to the nature of the wine. The rendering insoluble of a 

 portion of the tannoid matters carries with it the precipitation of 

 other colloid matters, such as the albuminoids, or the soluble com- 

 bination of tannin and albuminoids becomes insoluble when oxidised 

 as in the following experiment : — 



An aqueous solution of cream of tartar at 2 grammes per litre 

 (roughly 4J ounces per gallon) is alcoholized to 10 per cent, and to 

 it is added 1 gramme of tannin, and then an equal quantity by 

 weight of albuminous matter in solution, albumen, protein, casein, 

 etc., so as to determine a precipitate in the liquid as in the fining 

 of the wine. After a few hours rest the liquid is filtered, and in 

 the clear liquid resulting the acidity of the cream of tartar is saturated 

 with caustic potash, very slightly in excess of complete saturation. 

 Soon the liquid develops a more or less deep greenish colour though 

 at first quite limpid. Little by little this limpidity diminishes, and 



