Published in LETTERS on BREWING – Journal of Hantke’s Brewing School (1903)
The Causes of Boiling Fermentation
by Hartwig Harders. Paper read before the North – Western Brewmasters’ Association, Milwaukee, April 6th, 1903.
Among the abnormal fermentation phenomena frequently occurring in breweries, is the boiling or bubbling fermentation. Although in most instances it passes off without evil consequences, nevertheless, we are very much interested in determining its cause as nearly as possible. I have in the course of my observations recorded a few points that I might bring them here for discussion. The more carefully we study such an occurrence, the more readily we can prevent or avoid it, and I shall, therefore, not be reproached with having introduced a subject of which we would rather not hear anything said.
The mechanical cause of a boiling fermentation unquestionably lies in a premature settlement of the yeast, i.e., the yeast is deposited before its fermentative function is completed and the readily fermentable extract has been consumed. That such is the case we can demonstrate to our satisfaction by a simple experiment. We take a deep glass with a round bottom, a wide test tube will best answer the purpose, fill it with wort from the pitching tub in the rising kraeusen stage and allow it to stand at cellar temperature for 24 hours. On account of the low temperature the fermentation will be interrupted, and the yeast will settle to the bottom. If the glass is now brought into ordinary living temperature, the fermentation will speedily be started again and we shall have a miniature reproduction of a boiling fermentation. The development of carbonic acid proceeds from the bottom of the vessel, and we shall note that a hollow space is formed beneath the yeast layer, through which the wort circulates. The carbonic acid, as it accumulates, ascends through an opening, carries with it bound carbonic acid and thus causes an ebullition of the fluid.
In practice, too, we can easily obtain similar proof; if in a tub in which a boiling fermentation is in progress, we stir the yeast up from the bottom, all the carbonic acid accumulated beneath it will be set free and such a marked development of foam will occur that a normally filled tub will rise far above the edge and work over. The boiling condition will then cease, and when the proper time has elapsed the fermentation will have been properly completed, better than has usually been the case. So much for the mechanical cause of the boiling fermentation, but we are interested in knowing its exact cause. Why does the yeast settle prematurely? It is stated that one cause is cold ventilation in the cellar, which by cooling the surface of the wort disturbs the yeast in fermentation. This is really the same as occurs in our experiment with the test tube above described. It is also advanced that the sedimentary matter which passes with the wort from the pitching tube into the fermenting tub may be the cause, dragging the yeast down with it, as it settles, to the bottom of the tub. Both causes may, under certain circumstances, be correct without being the normal cause of the trouble.
I believe that in most cases the cause must be sought in the hops.
In a brewery working with uniformly good material and good yeast, a hop disintegrator was installed in order to economize in hops. When fermentation was started in a certain beer, the boiling fermentation was noted, and every effort was made to discover the cause without success. When the beer was casked, a sample of the yeast was sent to the scientific station and the report came back that the cells were coated with hop resin and could not develop. I may add here that the hops were disintegrated between steel brushes, so that leaves and stems were broken up and possibly the resin, also the oil partly pressed out of the glands.
Later I had an opportunity myself to examine yeast obtained from a boiling fermentation. I did not find the cells enclosed in a hop resin, but I discovered that most of the cells had little excrescences attached to the outside. At first, I thought they were bacteria; as, however, they were immobile and very sharply defined, I soon recognized them as hop resin. An attempt to dissolve them in natron-lye or ether did not succeed, because when exposed to these fluids for long, the yeast was likewise destroyed. When I came to examine the hops we were using, I found that they were over-ripe and dry, so that in the kettle the leaves were all detached from the spindle. I surmise, therefore, that in the case of over-ripe hops, where the petals have become detached from the spindle, much resin of an abnormal character finds its way into the wort, just as appears to be the case when the hops are too finely disintegrated with the aid of a machine. During the fermentation these little resin globules attach themselves to the yeast cells and so weight them that they can no longer float, but sink to the bottom quickly.
For this reason, also, yeast from a boiling fermentation is usually somewhat slimier and darker, in consequence of a hop resin attached to it.
I believe also that I have noted a very radical change in the mashing process or in the fermenting and pitching temperature may also cause boiling fermentation, because the yeast will not at once find its accustomed nutritive substances or temperature conditions, so that its earliest development will be retarded and it will be induced to settle prematurely.
Where one of the reasons last given is the cause, the phenomena will not occur next time the yeast is set, because it will have accustomed itself to the conditions. Where the cause lies in the hops, however, the boiling fermentation will not cease until the offending hops are all used or until they are so blended that the undesirable effect will no longer be produced.
This paper, which the referee had the pleasure to hear personally, was greatly applauded by the large gathering, and called forth a lively discussion, in which especially the brewmasters, Henry Hoerl, F. Theurer, Oscar Mueller, John Kraft, Carl Kieferle, William Jung, Oscar Husting and Ernst Hantke took part.
During this discussion still other causes for the boiling fermentation were brought from practical experience. As , for example: A slanting position of the fermentation vats, vats occupying a position in the vicinity of the cellar door, whereby a draft occurs, heated malts, etc.
Furthermore a discussion in regard to the hop-tearing machine was started and the opinions in regard to its advantages were divided; while a few recognized a better utilization, others were of the opinion that through smearing too much lupulin, consequently too much of the best material of the hops is lost, and that through the tearing too many particles of leaves enter into the wort and there have a disturbing effect, and thus might also be the cause for boiling fermentation.