Bottom fermentation, beer

Bottle seals Bottling Bottom-fermented beers... 

Since the 1960s the overall number of types has been decreasing, or at least remained unchanged (standard products), but some figures indicate that in the future the creation of new products might take place as a strong alternative to the previous mass-produced beers of less body or character. A traditional and overall grouping of beer can nevertheless still be made, ie, bottom-fermented beer and top-fermented beer. 

In 1903 Claussen obtained a patent in England for his process of adding Brettanomyces yeast "to impart the characteristic flavour and condition of English beers to bottom-fermentation beers and for improving English beers" (3). At that time it was unknown how the wine-like flavor developed in British beers. Brewers used the method developed by Hansen in 1883 for the inoculation of pure yeasts in bottom fermented beers however, they were unsuccessful in their attempts to use the method to recreate the flavors of well-conditioned top fermented English stock beers. These were stored in cask, vat or bottle for more than a week after racking. 

Table 5.18 Different types of beer According to the used yeasts the beers are classified in top-fermenting and bottom-fermenting beers...

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. 

Carbon dioxide is responsible to a substantial extent for the refreshing value and stability of beer. CO2 is 0.36-0.44% in bottom fermented beers, while in Weiss beer the CO2 content is up to 0.6-0.7%. A CO2 content below 0.2% gives flat and dull beers. Apart from small amounts of lactic, acetic, formic, and succinic acids, beer contains 9,10,13- and 9,12,13-tri-hydroxyoctadecenoic acid. In fact, 9.9 2.1 mg/1 were found in five types of beer and 9(S), 12(S), 13(S)-trihydroxy-10(E)-octadecenoic acid was the main compound and accounted for 50-55% of the 16 stereoisomers. The pH of beer is between 4.7 (dark, strong beer) and 4.1 (Weiss beer). 

There is a distinction between top and bottom fermented beers. 

Fermentation is carded out in two different, very distinct ways top fermentation and bottom fermentation. The governing principles are the same in both processes the chief differences are in the type of yeast and temperature employed, and consequently the method used for collecting the yeast after fermentation is finished. The alcohol content and, to a higher degree, the taste and stabiUty of the beer, are directly dependent on the normal progress of the fermentation. 

Lagers comprise more than 95% of the brew sold in the U.S. A., but just over 40% of the beer sales in Canada, and less than 5% of the beer sold in the U.K. More than 50% of the beer sold in Canada and nearly 90% of that sold in the U.K. is an ale. The basic difference between these brews is that, an ale is produced by a top-fermenting yeast, such as Saccharomyces cerevisiae, from which the yeast is skimmed from the top of the beer on completion of fermentation. Fermentation with these yeasts is carried out at 15-20°C, slightly higher than bottom fermentations. Ales are also hopped at a higher rate than lagers, which gives the product its characteristic more bitter, hoppy flavor. 

The distinctions between the yeast used in ale and lager brewing are small. Traditionally, ale yeast were regarded as top fermenters that formed a frothy yeast head on the surface of the fermenting beer, which was skimmed off to be used for subsequent brews, while lager yeasts were bottom fermenters that formed little surface head and were recovered from the bottom of the fermenter (Briggs et al., 2004). Today, this is a less useful distinction as many types of ale yeast now have the capacity to fall out of solution and settle at the bottom of the fermenter (Adams Moss, 2008). 

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.

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