Occurrence of Brettanomyces in American Lagerbeer.
American Brewers’ Review Vol. XIX, No. 11
Communication from the Wahl-Henius Institute by N. Hjelte Claussen. (November 1905)
On a former occasion I showed (Jour. Inst. Brewing, X, No. 4, 1904, and Wochenschrift f. Brauerei, No. 26, 1904) that the characteristic odor and taste of the English stock beers of which, for instance, Burton pale ale and Dublin stout are known all over the world as typical representatives, is caused by a special fermentation organism belonging to the group of the torulae.
As stated in the places quoted, this organism, to which I gave the name of brettanomyces, can be isolated from every bottle of typical ale and stout, and, inoculated into pasteurized beer or beer fermented with pure yeast, it causes an unmistakable English character. It is, however, as far as present experiences go, only in top fermentation and rather completely fermented beers that the resulting taste becomes pure and harmonious. If ordinary hopped wort is fermented with brettanomyces, a sourish liquid of impure taste is obtained in which the fine aroma of the English beers can hardly be discovered, and the conditions are similar, though not quite so pronounced, if a wort only partly fermented is inoculated with brettanomyces. Hence this fungus is absolutely useless for any kind of principal fermentation.
It is also ill suited for the secondary fermentation of low – attenuated beers because the resulting taste is inharmonious and impure. On the other hand, the secondary fermentation of top-fermentation beers, especially the English beers, is the proper field of the brettanomyces, and here it has done the work for ages, though unknown.
This shows that brettanomyces would be an unwelcome guest in most beers, only the English forming an exception, and only in these is brettanomyces present in such abundance that it can be isolated without special cultivation. It can hardly be supposed, on the other hand, that the occurrence of brettanomyces is limited to the British Isles or to the British breweries, and, indeed, it has been found that this is not the case. According to a verbal communication, Mr. H. Schioenning has been able to isolate brettanomyces from a number of Danish beers. But he was obliged to subject these beers to treatment suitable to the properties of the fungus so that the brettanomyces cells, originally present only in small numbers, could materially increase. Recently I also found brettanomyces in American lager beers, and according to experiences in the laboratory of the Wahl-Henius institute, its occurrence in lager beers generally is not a rarity.
As a rule, this occurrence has no practical importance at all. Brettanomyces requires for its development higher temperatures than those usually obtaining in lager beers, and the isolated individuals occasionally present do not make themselves felt at all. Only after the bottle beer has been exposed to a comparatively high temperature in the laboratory in order to be tested for stability by this “forcing,” does brettanomyces begin to develop and to display its activity. This causes a strong tension in the bottle so that frequently part of the contents is lost in opening, and the beer assumes a peculiar, impure taste slightly resembling English beer, which is at once recognized as soon as the attention has once been directed to it.
So it has been shown that cells of brettanomyces capable of development are not at all rare in the various beers, but nevertheless the infection has real importance only for certain English beers, and in this case it is not a mere accidental, but a desired effect, essential for the beer type in question. (I think it very probable that brettanomyces also plays a role in the production of some special beers, as, for instance, the Graetzer beer and the Belgian spontaneous fermentation beers, though I have had no opportunity to investigate this question.)
A closer consideration of these facts leads to suppositions concerning the origin and progress of brettanomyces infection, which very probably apply equally to other infections.
Inasmuch as brettanomyces occurs occasionally in very-different beers, there is probably a scantily but rather continuously operating source of infection in nature, from which a small number of germs, dependent upon the season and numerous local conditions, is introduced into the breweries, but here the fungus usually finds very insufficient conditions of life, and is for this reason retarded or altogether suppressed in competition with other organisms. It is especially washed away, so to speak, by the steady stream of pure yeast which is conducted through a modern brewery. This is the first stage of the infection which can hardly be entirely avoided, and which is usually not perceived at all.
If, however, the organism in question in exceptional cases finds favorable, conditions of life it begins its specific action, growing strongly the while. This is, for instance, the case if a bottle of beer containing traces of brettanomyces is kept in the thermostat of the laboratory, or, in general, if fermented beer is exposed to higher temperatures for any length of time. The infection is then in its second stage. The infection material continues to be introduced sporadically from outside into the brewery, but the conditions in the brewery may allow acute cases of the real “disease” to develop.
If the conditions in the brewery are frequently or perhaps continually favorable to the growth of the organism in question, the second stage passes into the third. The organism increases enormously within the brewery, and there are formed new foci which constantly disseminate fresh infection material of the strongest kind, independent of outside conditions. The “disease” has then become chronic. It will always come to the surface unless the conditions for its development are altogether too unfavorable. The brettanomyces of English breweries affords a typical example of such an infection in the third stage. Though unknown up to recent times, and for that reason appearing simply as an infection, the brettanomyces has settled here so permanently that its activity in the stored beer scarcely ever fails to appear. The cause for this must be found in the favorable conditions of life offered to the brettanomyces in the beers, which are stored comparatively warm. Where such favorable conditions exist, the brewer will have trouble, even if he observes the strictest cleanliness, to restrict the infection to the comparatively harm less second stage. There remains, in fact, in most breweries places where effective cleanliness is very difficult, and which for this reason may become foci for such internal infection, which cause the infection to enter into the third stage.