Bottom-fermenting yeast strains

Fig. 39 Rate of degradation - left - (expressed by the relative decrease of the proportion, in the C Is peak, of components due to carbon bound to O or N, divided by the time of exposure to X-rays) and water contact angle - right - of bottom- (open square, exponential open circle, stationary ceUs) and top- (closed squares, exponential closed circles, stationary cells) fermenting yeast strains as a function of the cell-surface concentration (weight %) of (a) proteins, (b) hydrocarbons, and (c) polysaccharides, as obtained by modeling XPS data ° ...

Flocculation. The exact degree of flocculence is very important for both top- and bottom-fermentiog yeasts. If the yeast is too flocculent, a large portion rapidly settles out, delaying fermentation. If the yeast is too powdery, the fermentation is rapid but the yeast does not settle out at the end of fermentation. Genes involved in flocculation have been identified physical and chemical factors such as divalent cation (Ca and Mg) concentration, pH, temperature, and net cell surface charge also play a role. In some strains, flocculation is apparently affected by haidike appendages, fimbriae, on the cell wall. 

This yeast strain is excellently suited for the production of bottom-fermented beers of all types. The resulting beer possesses an extremely pure flavor, a fine, subtle aroma, and a mild overall Impression. Fermentation is rapid with optimal yeast flocculation. The length of time that the yeast remains in suspension is dependent on conditions present in the brewery. The degree to which the color lightens during fermentation is sufficient. 

Figure 5.1 Description of Saccharomyces pastorianus ssp. carlsbergensis TUM 34/70, a bottom-fermenting lager yeast strain, in terms of fermentation parameters, beer-quality parameters, and aroma.

Differences in top- and bottom-fermenting brewing yeast strains... 

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