ACID] 'I' \ <>l- WINK. 407 



Here the volatile acidity --teadil} rose with the sugar concen- 

 tration of the must, nt)twithstanding the fact that the alcohol 

 formed got less when 24 per cent, sugar was passed. In order 

 to check these results similar experiments were made with the 

 same and other yeasts with sugar concentrations of 20, 35. and 50 

 l)er cent. respecti\ely. Here, as well as in the preceding' experi- 

 ments, the bottles containing' the experimental must were steril- 

 ized with cotton-wool plugs, and these were replaced by sulphuric 

 acid air-seals only wdien the yeast had grown so far as to render 

 the must turbid. The following are some of the results thus 

 iil)tained : 



Sugar Concentration. Steinberg, 1893. Piesport. Bordeaux. 



\'olatile Acid. Volatile Acid. Volatile Acid. 



20 



35 

 50 



These results ifully contirni the first o-ik-s. whilst they clearly 

 bring out the fact that different \east> form different amounts oif 

 volatile acid. Von der Heide furtlier showed that when experi- 

 menting with small c|uantitie> of must mure volatile acid is formed 

 than when the quantity of must is increased. 



In 1912 Osterwalder i)ublishe(l the results of .some \ery ini- 

 l^ortant experiments he had conducted cm the formation of volatile 

 acid by pure cultures of wine yeast. Me worked with a number 

 of different wine yeasts which he had isolated and cultivated in 

 pure cultures, and included a standard wine yeast, Steinberg 3. 

 for the sake of comparison. In his first set of experiments he 

 l^lugged all his 'lx)ttles with cotton-woul and kept tliem at the 

 temperature (winter) of the room, which was about 16 tleg. C 

 Half were filled with the juice of the Theiler pear, and half with 

 Sicilian grai)e-juice. Here I shall consider only the latter. He 

 inoculated with active {Aire cultures on the 8th October, 1910. and 

 analyzed one lot on the 25th February, 191 1, and the remainder on 

 the ist April, 191 1. On the whole the results obtained on these 

 two dates were practically the same, showing that no appreciable 

 amount of volatile acid was either formed or destroyed after the 

 2!;th Februarv, when the exnerniie.nt bnd lri>;t<>d four and ;i ha'f 



