1684 INDUSTRIES DEPENDING ON PLANT PRODUCTS 



and combined sulphur dioxide is reached which varies with the nature of 

 the must and the total amount of dioxide. Certain changes, however, in 

 the nature of the nuist appear to have no api)rcciable influence on the pro- 

 portion of combined dioxide; such are changes of acidity within ordinary 

 limits and the the direct action of Bolryiis cinerea. 



2) Sulphur dioxide forms a chemical combination with the aldehyde 

 in the must and is thus completely retained in the wine. The aldehyde is 

 produced by the action of yeast on sugar in the absence of air and when 

 combined with sulphurous acid it escapes much more easily from all hy- 

 drogenising and hydrolising actions, which are at their strongest when 

 the yeast has reached its maximum growth and the sugar has grown less. 



3) In spite of the greatly reduced antiseptic properties of sulphur 

 dioxide when combined, its presence in a fermenting must can modify the 

 physiological action of the yeast. The increase in production of aldehyde 

 is a proof and further experiments woiild produce others; an analysis of 

 the products of fermentation wovild show this. 



The rate of fermentation is lightly lessened even bj^ a small amount 

 of combined sulphurous acid not exceeding 200 mgms. per litre, especially 

 at first, and if the temperature is somewhat low; at 250 C. the retarding 

 effect is nmcli less than at 15°. 



Finally, the selective afiinitj' of the yeasts seems to be so nmch in- 

 fluenced by it that the proportion of glucose to fructose becomes higher 

 than I during fermentation, and this influence should be studied further 

 because of its effect on the constitution of sweet wines. 



4) The proportion of combined sulphur dioxide in cheap table wines, 

 (" vin ordinaire ") does not differ verj' much from that in the must which 

 produces it. But in the case of a grape must infected by Boirytis cinerea 

 and very rich in sugar, the sweet wine it gives rise to has generally a much 

 smaller combining power, very much the same as that of a " vin ordinaire ". 



The addition of sulphur dioxide to a must changes but little the com- 

 bining power of the wine obtained from it, for the initial dioxide is taken 

 up by the aldeh3'de and the product formed is more or less independent 

 of the other ingredients of the wine. But of course this initial combined 

 sulphur dioxide is extra to the amount of combined dioxide formed by 

 a later addition. 



The checking of fermentation can be done in contact with living yeast 

 without using excess of sulphurous acid, so long as enough acid is added 

 to stop the fermentation completely, and that the lees are withdrawn as 

 speedily and completeh^ as possible. 



Several factors may necessitate an increase in the total amount of 

 dioxide needed to preserve sweet wines; they concern the method of wine- 

 making, and the later treatment given to these wines. Thiis, excessive ae- 

 ration and a too ]jrolonged fermentation favoiirs the formation of aldehyde, 

 and consequently the combination of sulphurous acid; but piecipitation 

 in presence of sulphurous acid and secondary fermentation after sulphit- 

 ing have a greater effect in increasing the amount of sulphur dioxide which 



