The production of pure yeast for brewing purposes has been put on a practical basis of late years through the scientific researches of Dr. B. C. Hansen, of the Carlsberg Institute, in Copenhagen. He succeeded in producing a pure yeast cultivated from a single cell. He was able to differentiate in this way six different species or varieties of saccharomy-cetes, several of which may usually be found in an ordinary brewery yeast. These different varieties have been shown to produce beers differing not only in coloring, flavoring, facility of separation of the yeast, etc., but also in chemical composition.

In a recent address before the Society of Chemical Industry by G. H. Morris,1 a resume is given of the work done in this direction by Hansen and others.

Dr. Morris states that the employment of the pure yeasts is coming very largely into use in the beer-drinking countries of the Continent, and has met with favor from some of the most noted brewing technologists, such as Jacobson, Aubry, Miirz, and Lintner, the latter of whom sums up the question in the following statements:

(1) By contamination with so-called wild yeast an otherwise normal brewery yeast can he rendered incapable of producing a beer of good flavor and with good keeping qualities.

(2) A contamination with wild yeasts may be produced by the dust of the air during summer and autumn, by the malt, or other sources.

(3) By employing Hansen's method of pure cultivation and analysis it is possible to obtain from a contaminated yeast a good brewery yeast in a state of purity.

(4) Yeast cultivated in a state of purity possesses in a marked degree the properties of the original yeast before contamination as far as concerns the degree of alteration of the flavor and keeping qualities of the beer.

(5) There exist different varieties of normal bottom yeast (S.cerevis.), each with special properties which, like the peculiarities of species, are maintained constant.

The use of this yeast has not yet extended to England, although experiments on an industrial scale are now being carried on at Burton-on-Trent with different species of pure yeast.

The chemical characteristics of beer made from the different species of pure yeast have been investigated by Borgmann,2 who analyzed samples of beer produced from two species of pure yeast, each cultivated from a single cell and the beer fermented under comparable conditions. The analysis gave the following results :

From these numbers, which are the means of many determinations, the analyst concludes that the different yeasts produce beers which differ in chemical composition. He also finds that the proportion of alcohol to glycerol is different from that formed with other beers. From analyses of other beers he finds that the proportion is -

1 Jour. Soc. Chem. Ind., 1887, p. 113

2 Zeit. Anal. Chem. 25, 532.

while with the Carlsberg pure yeast the proportion is -