i8o CHEMISTRY OF THE YEAST^CELL. 



the precipitated mucinous matter carries down the yeast cells, 

 but not the brown hop resins, &c. 



The foregoing explanations may also prove useful in practical 

 analytical chemistry, namely in cases where the percentage of 

 sugar in wine and similar liquids is to be determined with the 

 aid of Fehling's solution. In such event it should be re- 

 membered that this reagent also precipitates the gummy sub- 

 stances present, the resulting precipitate of cuprous oxide also 

 including the precipitated copper compound of the gum ; con- 

 sequently too large an amount of copper is weighed, and the 

 quantity of sugar calculated therefrom will be far in excess 

 of the truth. This applies more especially to the so-called 

 yeast wine, which is an inferior wine obtained by pressing the 

 sediment (the so-called wine yeast) from the wine casks. This 

 sediment is very rich in gum, and therefore (as was shown by 

 K. Amthor (III.)), should not be examined for its sugar content, 

 by the aid of Fehling's solution, without bearing this in mind. 

 With the said yeast wine, in this respect, must be classed the fruit 

 wines (mostly very rich in mucinous matter) and such grape wines 

 as have been racked from the yeast very late, and have therefore 

 absorbed large quantities of gum from the latter during the 

 protracted period of contact therewith. It may also be men- 

 tioned that certain gummy substances find their way from the 

 grapes into the wine must, and that experiments have been 

 made by G. Niviere and A. Hubert (I.) with regard to the 

 gum recoverable from wine. Gummy substances are also found 

 in malt, having been isolated therefrom by 0. J. Lintner (IV.). 

 It may occasionally happen that such a gum, when not 

 eliminated during mashing and boiling, renders the beer 

 dichroic, instances of which kind have been reported by 

 H. Will (XI.). 



§ 255.— Albuminoid Mucinous Substances. " Head " 

 and Frothy Fermentation. 



The netwoi'k enveloping the yeast cells is not invariably 

 composed of the carbohydrate gums described in the preceding 

 paragraphs. Careful investigations performed by H. Will 

 (VII.) have shown that, in the case of a considerable number 

 of stocks of beer yeast, the enveloping, agglomerating netwoi'k 

 is constructed of a material that gives all the reactions of 

 albumin. This albuminous matter is more abundant in the 

 upper layer of the sedimental yeast found in the fermenting 

 tun at the close of primary fermentation, but is less plentiful in 

 the lower or core yeast ; and it differs from the other albuminous 

 admixtures present therein, not only in its lack of definite foi'm, 

 but also in point of origin. From the fact that it is also encoun- 

 tered in cultures grown in nutrient solutions free from albumin, 



