540 ENZYMES DECOMPOSING SACCHARIDES. 



The fermentation residue is tested for dextrin by a special method 

 given by the same author (I.e.). 



LINTNER (XII.) opposed the views of Medicus, Fresenius and 

 others by asserting that the earlier experiments were inconclusive, 

 having been performed with impure dextrin or impure yeast. The 

 dextrins in starch sugar are partly reversion products, such as the 

 gallisin of SCHEIBLER and MITTELMEIER (IV.) ; and the pressed 

 yeasts are not composed of uniform organisms, but contain many 

 bacteria capable of attacking dextrin. Malt dextrin is unfer- 

 mentable by pure yeast of Sacch. cerevisice type ; and the numerous 

 conflicting reports may also be explained by the circumstance that 

 many of the workers employed dextrins containing sugars, and 

 not the pure substance. E. von Raumer's observation of a 

 difference in yeasts, inasmuch as pressed yeast attacks dextrin 

 most powerfully, beer yeast acting in moderate degree, and wine 

 yeast not at all, renders it fairly certain that his pressed yeast 

 contained large numbers of bacteria, and the beer yeasts probably 

 contained film yeasts, whilst the wine yeast was relatively pure. 

 SHIFFERER (I.) also reports that malt dextrins resist the action of 

 pure top yeast, though they are eliminated by treatment with 

 impure commercial pressed yeast. 



A new stage in our knowledge of dextrin fermentation was 

 reached when the study of yeasts led to the establishment of 

 certain definite types in the Sacch. cerevisice group. This was 

 stimulated by the discovery of Saaz yeast (see p. 112, vol. ii.) and 

 the differentiation between the Saaz and Frohberg types, the 

 former of which gives a lower final attenuation than the latter. 

 Since both top and bottom yeasts form well-defined races, we 

 have the types : bottom Frohberg, bottom Saaz, top Frohberg, 

 and top Saaz, distinguished by the signs: UF, US, OF, OS 

 respectively. Yeasts of the OF and UF type produce the same 

 final attenuation in beer wort, OS and US being also equal in 

 this respect. It is true that insignificant fluctuations occur in 

 one final attenuation, since the yeasts do not merely ferment the 

 carbohydrates, but also assimilate and modify a number of other 

 wort constituents, especially nitrogen compounds and salts, besides 

 producing non-volatile products, especially glycerine and succinic 

 acid (see p. 490) in varying quantities. This explains why the 

 residual extract in one and the same wort that has been fermented 

 by different yeasts, e.g., of the UF type, is not identical in all 

 cases, but frequently exhibits small differences. 



In addition to the foregoing, H. VAN LAER (III.) established 

 the Burton type of yeast, which ferments worts to a greater 

 extent than the UF yeasts. He also differentiated intermediate 

 types* giving an attenuation midway between the types already 

 mentioned, and named them Saaz-Frohberg and Frohberg- Burton. 

 These types, however, never found acceptance in fermentation 

 physiology; and, in fact, VAX LAER (XII.) himself partly aba n- 



