FERMENTATION PHENOMENA. 435 



since the acidity of the liquid is diminished, rather than increased, 

 by the conversion of the aforesaid organic acids into lactic acid, 

 this cannot explain the considerable increase of the total fixed 

 acids reported by Amthor. Unless one is disposed to assume that 

 the newly formed acid is succinic acid exclusively, it must be 

 concluded that fixed acids of some other kind are also formed 

 during fermentation by Apiculatus yeasts. 



The well-defined power of Sacch. apiculatus of producing 

 volatile acids in large quantities has already been mentioned on p. 

 ^427, vol.ii., together with the figures of production given by various 

 workers. In the opinion of MtiLLER-TnuRGAU (XI.), these volatile 

 acids constitute a weapon by which this fungus is able to restrict 

 the development of other yeasts. The nature of these volatile 

 acids, however, cannot yet be precisely stated. In any case, as Jj 

 AMTHOR (I.) showed, by the preparation of the silver salt, they 

 consist only partly of acetic acid ; and moreover, according to 

 MULLER-THURGAU (XVIL), the wines do not exhibit the charac- 

 teristic flavour of acetic acid. In experiments with a sterilised 

 nutrient solution containing ammonia salts, dextrose, and invert 

 sugar, and inoculated with Sacch. apiculatus, AMTHOR (II.) detected 

 in the distillate from the fermented liquid both acetic acid and 

 formic acid, together with traces of an acid boiling at 120- 12 5 C. 

 The fixed acids consisted of succinic acid and lactic acid. The 

 first-named probably combine in part with the alcohol to form 

 esters, which do not taste or smell sour in the liquid, but are 

 decomposed in distillation so that the acid is available for deter- 

 mination. These esters, which Sacch. apiculatus is capable of 

 producing to a larger extent than other yeasts, are the chief cause 

 of the fruity flavour exhibited by the musts, worts, and fruit 

 juices fermented by means of this fungus. According to the 

 experiments of W. SEIFERT (IV.), Sacch. apiculatus produced a 

 larger quantity of volatile esters (together with 0.064 per cent, of 

 volatile acids) from one and the same grape must than was fur- 

 nished by six pure-culture yeasts. The ester content, expressed 

 in c.c. of decinormal alkali per 100 c.c. of wine, was 10.8 ; whilst 

 in the case of the other yeasts it ranged between 1.32 and 4.4. 

 P. LINDNER (VII.) observed an extensive production of fruity 

 ethers by an Apiculatus yeast, more particularly when the liquid 

 under fermentation was vigorously aerated and contained a suffi- 

 ciency of dextrose. In addition to the sweet-smelling esters, 

 Apiculatus yeasts may also produce other kinds of odorous and 

 flavouring substances under certain conditions. In fact, H. 

 WILL (V.) succeeded in effecting a means of differentiating the 

 various species isolated by him, as pure cultures, from wort, beer, 

 grapes, &c., according to the character of the smell they produce. 

 One series is distinguished by the mouldy, fusty smell of the 

 cultures, whilst another exhibits a very decided bouquet (fruity 

 smell) resembling amyj^jether. In saccharine yeast water they 



