MEETING HELD AT THE MIDLAND HOTEL, MANCHESTER,
ON THURSDAY, APRIL 28th, 1910.
Mr. James G. Wells in the Chair.
The following paper was read and discussed :—
Lager Beer. Part III.—Fermentation.
by C. Rühl
In an earlier paper (this Journal, 1910, 16, 247) I mentioned that bottom-fermentation beer was the precursor of top-fermentation beer; but it is doubtful if the yeast race, now known as “bottom-yeast,” was in reality derived from top-fermentation yeast. This doubt, and the circumstance that neither the present state of science nor any other source supplies an exact answer to this question, justifies the inquiry: What was the origin of fermentation? We may suppose that fermentation is nearly as old as earth itself, and that alcoholic fermentation has set in, as soon as there was any sugar-bearing matter existent, to which air-dust supplied the ferments. Thus, alcoholic fermentation is very much older than the human race.
Looking round in nature, we find alcoholic fermentation wherever sugar-bearing plants grow—in forest and field—everywhere we see nature’s brew houses, and may watch nature preparing alcoholic beverages of different kinds.
Bottom-fermentation is one of the youngest branches of this ancient pedigree, and its cradle stood, as I have said before, in the vaults of the Bavarian Cloister, Weihenstephan.
Whence the monks there obtained the race of bottom-yeast I cannot say. Cloisters at all times have been homesteads of science, and if the yeast employed at Weihenstephan during those early times was in reality of bottom type, it presumably must have been the result of long series of years’ experimenting with wort at different temperatures exposed to air.
Liebig regarded ferments as nitrogenous matter, acting under different conditions, at one time as vinous ferment, at another as lactic, acetic, viscous, putrid, etc. According to his view, nitrogenous bodies, in presence of moisture and air, underwent oxidation, and induced a similar state of change in other unstable bodies present, as, for instance, in sugar. The latter was split up into simpler form, and the former thrown out of solution as yeast.
By means of this hypothesis, now out of date, Liebig rendered very valuable service to the brewing industry, especially to Bavarian brewers, by giving advice how to conduct low fermentation.
Pasteur, brought up in a country where wine is produced on a large scale, collected and grouped the observations of other microscopical investigators, and he found out and proved that fermentation was due to the development of actual cell life.
Bail, in endeavouring to find out the origin of beer-yeast, came to the conclusion that there must exist several ferments, each having its own specific properties and peculiarities, and he first pointed to the necessity of pure culture.
Brefeld, who isolated a single mould spore and studied its development, made the next important step towards clearing up the possibility of pure culture, and then came E. C. Hansen’s epoch-making investigations, founded on a method of separating a single yeast cell, and growing from it a sufficient quantity of yeast for pitching a whole brew.
I do not intend going into details of Hansen’s system, as this would be quite unnecessary; but I would point out that, thanks to Prof. Hansen’s system, every brewer may now cultivate exactly those varieties of yeast that suit his purpose best; the fear of his fermentations being spoiled by the influence of bacteria is reduced to a minimum, and the fermentation process, being, as an additional security, kept under sharpest control, biologically and chemically, can develop under the solo governance of Saccharomyces cerevisiae.
By the power of this small cell, acting as an anaerobic ferment upon the fertile field that our wort offers, the sugar is split up into alcohol and carbonic acid, and the struggle against bacteria is, from its beginning, entirely in favour of the yeast.
Let me be clearly understood. Yeast is known as an anaerobic ferment, but, of course, it does not and cannot normally develop when entirely out of contact with air. Free oxygen is absolutely requisite, especially at the earlier stages of development. In more advanced stages, when out of contact with air, the cell has the power of seizing upon the oxygen that the sugar offers, incidentally splitting up the latter, as mentioned above, and this should be carefully considered with regard to aeration.
In addition to alcoholic fermentation proper, by means of which certain carbohydrates are converted into alcohol and carbon dioxide, we now know that, during the development of yeast, decomposition of nitrogenous matter proceeds. We know that amino-acids are also converted into ammonia, alcohols, aldehydes and a number of different acids. This fact entitles us, in a certain sense, to speak of the alcoholic fermentation of albuminoids. In this process a number of substances are produced, which are free from protein, and which are supposed to influence largely the odour and flavour of the beer. The latter substances have, up to quite recently, been wrongly regarded as by-products of the ordinary fermentation of the sugars. Amino-acids are capable of being assimilated by yeast, and it is today an acknowledged fact that these acids play a prominent part in the development of yeast, supplying it with nitrogenous food.
It has been shown by F. Ehrlich (see this Journal, 1907, 13, 520) that the formation of higher alcohols (fusel oil), and, perhaps, of succinic acid (sec ibid, 1909, 15, 614), is due to the metabolism of these amino-acids by yeast.
I now propose giving a short description of the arrangement and construction of the buildings necessary for fermentation and storage rooms in lager beer breweries.
Starting at the top and going downwards, the coolers will usually be found on the top floor. There are no closed walls, the sides are open and fitted with louvres resembling large Venetian blinds. On the next floor below are the refrigerator and the sludge filter plants. Then follow the fermenting rooms, lower down the storage rooms, called lager cellars, and on the ground floor the racking rooms. The walls, ceilings, and floors of fermenting rooms and lager cellars must be carefully insulated, since the slightest communication of air between the inside and outside, due to faulty construction, means a loss. They must also be suitably ventilated, and the exact action of the ventilation arrangements is of greatest importance. All outlets (for water, etc.) must be constructed as syphons, or in any other way which will prevent undesired circulation of air.
For the purpose of insulation, Cork-Goudron plates have proved a very good material.
As the name suggests, low fermentation requires certain low temperatures. For this purpose cooling arrangements, either by means of ice or by refrigerating machine, are employed, and the rooms in which the fermentation is going on must be kept at a constant temperature of from 45—50° F. The lager cellars are usually kept at a temperature as near as possible to the freezing point. There are, of course, still many breweries, especially such as produce their beer on a small scale, having no ice-producing or cellar-cooling plant, yet the quality of their product is, not-with-standing, everything that can be desired. These breweries are furnished with natural ice-cooled cellars, in order to keep the temperature in lager and fermenting rooms at the necessary points, and ventilation arranged accordingly. They must also have separate collars containing the ice necessary for manipulation, that means for filling the “swimmers” (of which I have to speak later on in my paper) in fermentations and storage yeast, and they must also contain the ice that the customers must daily be supplied with. I may add that such an arrangement is quite as effective as an ice-machine plant, and sometimes works out cheaper in practice, provided that the ice supply is to be got from very near, and that the climate is such that every winter brings a sufficient quantity of ice. Ice cellars must of course be large enough to take sufficient ice for two years’ work.
Turning to fermenting vessels, I dare say that until very lately oak was considered the best material for making these, as well as lager casks, and there are still very many lager beer brewers on the Continent who would not change from their oak vessels to glass-lined steel tanks or anything else. So the upright oak vessel, open on top, taking 18—24 barrels, is still the one most commonly used. A certain number of these vessels are placed in a row in such a way that every vessel is easily accessible for every purpose—for manipulating as well as for cleaning inside and outside. It is, for the latter purpose, also advisable to leave at least 1 metre free space between the cellar floor and the bottom of the vessel.
In breweries having a freezing plant, every fermenting vessel is fitted with some stationary or removable cooling arrangement. Breweries not using ice-water coolers may place swimmers in the fermenting liquor, which, before the temperature has reached its maximum, must be filled with ice, in order to regulate the rising, and later on the reduction of the temperature, down to the necessary point requisite for the lager cellar secondary fermentation.
With regard to size, it was formerly thought of no use to make fermenting vessels larger than mentioned above, but, recently, opinions have changed, in so far as many brewers now prefer glasslined or enamelled iron or steel tanks, in some cases of very large size. They are highly esteemed, especially by American brewers, since they save labour, space, waste, etc., and therefore some American brewers use huge tanks, and similar ones may also be found in some Continental and English lager beer breweries.
But there are many pros and cons concerning every sort of material used for making fermenting vessels. Wood (lacquered, paraffined, pitched, or copper or aluminium lined), iron and steel (glass-lined or enamelled), cement, stone, or slate, or of whatever kind the material may be, each of them has its advocates as well as its opponents. Putting aside, therefore, the question of material, and falling back upon the size considered to be best, I may say that the consensus of opinion to-day is that fermenting vessels as well as lager casks may be made considerably larger than they have been hitherto without fear of any detrimental consequences. But they are best kept in accordance with output, and the way in which the brewery is generally worked should also be carefully considered. As to fermenting vessels, the height should not be much greater than the diameter, and breweries changing from wood to iron or steel tanks may have to raise the starting temperature for fermentation and the quantity of pitching yeast,
As far as lager tanks are concerned I should think it well worthwhile to reflect most carefully upon the fact that lager beer is a liquid saturated with gas, and whether an abnormally large lager tank might not involve some danger to this beer. It must be racked under pressure, the latter being mostly produced by compressed air. That does not prevent carbonic acid diffusing into the air. Now, (1) the larger the tank is the larger is the surface of beer exposed to the compressed air, and (2) the more time is required for racking the longer is the beer exposed to such possible loss. On the other hand, lager beer should be consumed as soon as possible after being racked into casks, and the latter circumstance alone is of sufficient moment for regulating the question of size for lager tanks. Wooden lager vats somewhat resembling very large union casks are made to meet every demand in sizes ranging from 5 up to 120 hectolitres and larger. They are, as mentioned before, made of oak, strong enough to stand the pressure which lager beer is allowed to produce towards the end of the secondary fermentation as well as the racking pressure. Every cask has a manhole cut into the middle piece of the front end wide enough to admit a workman, who has to clean the inside thoroughly each time it is emptied, since the lager casks remain in their places in the lager cellar for several refillings.
New lager casks must, before being taken into use, be steamed and pitched, that is to say, the inside must be covered with a thin layer of brewers’ pitch.
Some brewers have their casks repitched as often as they are emptied in order to saturate their beer with that characteristic fine bitter taste that freshly applied pitch gives to beers.
I will now retrace my steps and take up my theme at the point where my previous paper ended. I have already stated that the wort when leaving the hop copper passes through the hop back, from which it is conducted by means of a centrifugal pump to the coolers. It remains to describe these vessels and their purpose. Coolers are flat, shallow, iron vessels, their dimensions being calculated so as to allow 3½ square metres space for every hundredweight of malt (or equivalent of sugar). They must be coated with a lacquer which will stand boiling liquor, and their purpose is, as the name suggests, to allow wort to cool by exposure in very thin layers to a large surface of air.
Coolers answer this purpose insufficiently, especially in summer time, and besides they involve a great danger. The wort, being exposed for a comparatively long time to air in a large surface, runs the risk of being seriously infected by bacteria. Therefore, up-to-date breweries have done away with that vessel, and it has been replaced by closed vessels for the aeration of the wort by filtered, germ-free air, forced through it under pressure—this being done whilst the wort is still hot. Leaving the aerating apparatus or coolers the wort passes over a refrigerator of some kind, and is thus cooled down to the low temperature required. The latter is by no means a fixed temperature, and 41°—47° may be taken as about the minimum and maximum, though there may be exceptions in either direction.
When the wort is not filtered through the hops a certain quantity of sludge will remain upon the coolers, and this must be filtered immediately. Its quantity depends partly upon the quality of malt and partly upon the method of brewing.
From the refrigerator the wort is run into a collecting vessel and yeast added.
The quantity of yeast used for pitching depends in the first place upon the thickness of the yeast used for that purpose; but there are other considerations, such as the concentration and character of wort, size of fermenting vessels, the material of which the latter are made, and, further, the temperature of fermenting room. Generally speaking, the amount of yeast employed should not be kept down. For each equivalent of wort drawn from 1 cwt. of malt, 1 to 1½ litre of thick yeast will suffice. A larger quantity of pitching yeast accelerates the fermentation process, but does not interfere with the final attenuation. Again, if a fermentation is started at 41° F., and its maximum of temperature is not intended to be higher than 47° F more pitching yeast would be necessary than if the temperature were allowed to rise to 50° F.
I shall have more to say on lager-beer yeast, how it is gathered, treated, and kept, in a later part of my paper, hut I will now proceed with the description of the process.
The pitching yeast must he well mixed with wort and air and this is best done by means of a special apparatus. For this purpose Ritter’s apparatus for yeast and wort aeration is highly recommended. This apparatus supplies filtered air which thoroughly mixes the yeast and wort, thus considerably reducing the danger of infection, whilst it can also be used with great advantage for rousing. Frequent rousing is necessary, until the beginning of fermentation is distinctly visible.
As with bottom fermentation the wort is more in contact with air than is the case with top fermentation, every precaution must be taken for the prevention of the development of bacteria, and floor and walls of the fermenting rooms, as well as the exterior of the vessels, must be kept scrupulously clean, and washed with an antiseptic. Cleanliness is a main factor in all brewing processes, but especially where fermentation is concerned, though the comparatively low temperature adopted in bottom fermentation precludes, to some extent, the development of undesired organisms.
The fermentation of lager beer wort can be divided into two processes: (1) The main fermentation, carried out in the fermenting vessels, and lasting 7 to 10 days; (2) the secondary fermentation, which takes place in lager casks in the storage rooms.
As a rule, beer which is intended to be finished and sold for quick consumption should be allowed to attenuate to a lower gravity in the primary fermentation than such as is intended for a longer storage. A fermentation can be brought to a higher degree of attenuation by strongly aerating the wort in the beginning, to be followed by gentle aeration at intervals during the two succeeding days. It makes a difference whether the temperature rises quickly to the maximum and is then checked, or whether the temperature rises slowly to the maximum and is maintained there for some time before being lowered.
The choice of yeast is of greatest importance, and it does not suffice to buy a commercial yeast which possesses a certain attenuative power in another brewery, because experience proves frequently that yeast does not always show the same power when transplanted into other wort and subjected to other environment, as, for instance, from one brewery to another. As before stated, the quantity of yeast employed for pitching is of no moment in regard to the degree of attenuation. The temperature has some influence, but is not of so much moment as is sometimes suggested.
Malt flour increases the degree of attenuation—especially when the pitching yeast is weak, hut less so when a sound and strong yeast is employed.
Wort obtained from malt which has been finished at a high final will show a lower degree of attenuation than a wort derived from malt that was produced from the same green malt, dried off at a lower temperature, and this is the case even when the same brewing process has been employed. The water, which should be a good drinking water, has no special influence upon the attenuation, so far as the primary fermentation is concerned.
The action of alcohol is different upon different yeast races, so that the same brew, divided amongst separate vessels, each pitched with a different yeast race and fermented under otherwise similar conditions, may give distinctly different results.
A wort obtained from pale malt contains more readily fermentable sugar than a wort derived from Munich malt, when both are brewed on the same lines.
As to the extent of attenuation in the primary fermentation, no hard and fast rules can be laid down. This must be regulated according to whether a beer is intended for quick consumption or lengthy storage, and it also depends upon the materials and methods.
Towards the end of the main fermentation, the cells of bottom-yeast show a tendency to settle to the bottom of the vessel. The single cells draw together, forming small clots, the latter gradually sinking to the bottom. Lager beer brewers describe this formation into flocks by the term break, and this break is carefully observed and controlled during the last few days of the main fermentation. Very small glasses, called observation glasses, are filled with the fermenting liquor and examined. The beer should be absolutely bright, the little clots suspended should, when examined a few hours later, have settled down to the bottom of the glass in a compact mass, leaving the super-natant beer absolutely brilliant.
By this time the temperature has been reduced gradually to the desired point by means of an attemperator, swimmer, or such like arrangement in the fermenting vessel. The primary fermentation is finished, and the beer is to be removed to the lager cellars into the lager casks. The temperature considered to be best at this moment will depend upon circumstances, and is usually chosen between 36° and 41° F., according to the duration of storage, etc. Beers reduced to very low temperatures should be still rather fresh when stored.
It may not be out of place here to say a few words on yeast. When the beer is drawn from the fermenting vessel, the yeast will be found in a layer on the bottom of the vessel, and its consistence gives valuable indications as to its quality. A powerful and sound yeast always settles down in a compact mass, rendering strong resistance to the oar, by means of which it is usually removed from the fermenting vessel into a smaller vessel.
The whole yeast crop can be divided into three parts, taken from the entire surface. The top layer, discoloured by resinous matter, dead cells, and other undesirable substances, as well as the part nearest to the bottom of the vessel, is not used as pitching yeast. For this purpose only the yeast situated between these two portions is chosen and collected. Choice and gathering of yeast requires some experience and skill, and should not be entrusted to an ordinary workman.
The amount of outcrop is almost independent of the quantity of yeast used at pitching; 1 litre of yeast, pitched into wort of 14° Balling, will yield an average of about 2·6 litres of outcrop.
It is a matter of opinion whether a yeast may be more advantageously used when taken direct from the fermenting vessel or washed before being used.
When it is necessary to keep a yeast for a few days it should, immediately after being taken from the fermenting vessel, be thoroughly intermixed with cold water, passed through a horsehair sieve, and placed in a cold room called the “yeast storage cellar.” The super-natant water must be cooled, and this is accomplished by means of either the freezing plant or by swimmers filled with ice placed in the water. Lager breweries frequently change their yeast.
For sending on a long journey yeast should be pressed; 1 litre of wet yeast is equal to 450—600 grams pressed yeast.
I have already stated that the beer is removed from the fermenting vessel into the lager cask at a stage of attenuation suitable for the purpose. In these casks the beer remains always at the low temperature mentioned for two to four months and longer, and must sooner or later become absolutely brilliant without being treated with finings. Finings are consequently very seldom used.
In olden times brewers put hazel-nut shavings into the lager casks as a means of fining, but since filter plants are universally employed, lager beer brewers have, as mentioned before, done away with all sorts of fining.
The beer remains absolutely undisturbed until the time is reached when it must produce its condition. The consumer of lager beer desires—in fact, demands—that the beer when drawn off foams, so that the surface of the beer in the glass is covered with a creamy head, and this head must remain until the last drop is consumed. At the same time the beer has not only to be bright but brilliant, and it has also to be impregnated with carbonic acid, the latter, in the actual moment of consumption, giving that characteristic sensation, that inexplicable fine and mild sharpness called “condition.” In brief, I would say that the purchaser of lager beer demands that the beer shall contain a certain quantity of carbonic acid. Since for the manufacturing of lager beer in Germany only malt, hops, and yeast can be used, this condition is never an artificial one, but it is produced by properly regulating the secondary fermentation. Every lager cask or tank is accordingly fitted with a closing arrangement of some kind. As soon as this is kept closed the carbonic acid, which is continuously being generated, cannot escape, so that an actual pressure in the cask results; the beer becomes more brilliant and at the same time charged with gas. This process is called Spundung, and as there is not an equivalent word for it in English, I beg permission to make use of this expression.
Age, stage of attenuation, and temperature are the three main factors which determine the quantity of carbonic acid a beer may contain under normal atmospheric pressure. But, if a beer is charged with gas so that parts of the latter may be retained and kept in solution in the beer for some time, still, after the pressure is taken off (when the publican taps it), we have to apply a certain surplus pressure, or, better still, we have to submit this beer to a certain surplus pressure for some time. Sound beers will, during the first two months of storage, easily produce the requisite quantity of carbonic acid and, consequently, when bunged up, also the desired over-pressure. They need not be kept under pressure longer than from 7 to 14 days; but beers older than three months require to be kept under pressure for two to three weeks, and they should be treated with a small quantity of fermenting wort (Kräussen) sufficient to communicate fermentative action to the bulk. The lower the temperature of the lager cellar the less pressure is required, because the lower the temperature the more carbonic acid beer absorbs and retains. As an average may be stated younger beers require a pressure of ¼ atmosphere (3¾ lb. to the square inch), whilst for old matured lager beers 1/5 atmosphere (3 lbs to the square inch) will suffice, but such beer has frequently got a sufficient quantity of gas when kept at 0·15 atmosphere (2 lb. to the square inch).
The pressure should not be allowed to rise higher than 1/3 atmosphere, otherwise, over Spundung will occur. Beers having been exposed to more than 1/3 atmosphere (5 lb. to the square inch) for some time will, when drawn off, foam at first violently, but the carbonic acid will quickly escape, and flattening may very soon result.
Over Spundung can be avoided by means of different kinds of apparatus connecting a number of lager casks together, keeping these under the required pressure; the excess escapes out of the casks and is led to other casks where the pressure is lower than is required.
When the beer is thus sufficiently matured and conditioned it is drawn off. By means of an automatic pump (pressure-regulator) it is conducted through the filter into the iso-barometric racking apparatus, racked under counter-pressure perfectly bright, into trade casks, in which the beer still remains under a certain pressure until drawn off for consumption.
Trade casks, made of oak, to contain 5 to 100 litres, must stand 2 atmospheres (30 lb. to the square inch) pressure. They are also usually either pitched inside or paraffined. A Continental firm have lately placed on the market metal casks and an apparatus for pasteurising beer in trade casks for export.
The pitch used for pitching casks is the resin of conifers; the raw pitch must be boiled in open coppers in order to drive away the contained turpentine oil. The Black Forest, and the forests of Thuringia, Bohemia, and Tyrol supply the most appreciated qualities of brewers’ pitch.
A good pitch should show the following characteristics:—
It should possess as little flavour and smell as possible; its melting point should be between 95° and 129° F.; when dissolved in absolute alcohol it should not leave more than 0·4 per cent, insoluble substances. Further, blue litmus paper should show no reddening (no free acid should be present), and basic lead acetate should give no precipitate. Pitch should not contain more than 1·5 per cent, water; an alcoholic solution containing 4 per cent, alcohol should show no influence upon it at all.
I have, in an earlier part of my paper, mentioned that in some breweries the casks are repitched as often as the latter are emptied, in order to substitute for the beer taste that peculiar bitter that pine pitch supplies. But that is not the real reason why casks are pitched, and, in fact, very many brewers do not want their beer having a pitchy taste.
Casks are pitched for the purpose of preventing the air coming into contact with the beer, and to give a smooth surface to the inside of the casks, so that no yeast or anything else can find a resting place on it.
The actual work of pitching is done in very different manners, mostly by means of machines.
I should have liked to say a few words more with regard to pitching machines and to filter plants, and also with reference to the subject of the bottled beer trade, which during the last few years has grown to an enormous extent on the Continent, mainly because the breweries have taken the whole matter in their own hands, and now do a tremendous trade direct from the brewery bottling stores to the consumers’ houses; but the time at my disposal is insufficient.
The Chairman, after remarking upon the interesting character of the series of papers on the subject of lager beers read by Mr. Rühl, expressed the indebtedness of the section to him. With regard to aeration, he described an enormous shallow cooler he had seen on a visit to a brewery in Vienna, in which the beer was allowed to stand from the preceding night in order to cool to almost the pitching temperature. The result was that the wort showed a slight formation of film. He also alluded to the system he had seen in Munich, where the beer was conveyed some distance from the fermenting vessel in ox-drawn casks to the cellar storage; and, from an aseptic point of view, he claimed the English method to be preferable. He could not quite understand why, in such a carefully conducted industry as the lager beer industry, where everything was supposed to be carried out on modern principles, it should be necessary to wash the yeast, except it was that, despite every precaution, bacteria obtained a hold. With regard to coating the casks with paraffin wax, he said he had never heard of a lager beer brewery where this was done; but in the instances Mr. Rühl had given, he should like to know what success had attended the experiment. Mr. Rühl also spoke of pitching, but English brewers had always regarded this as producing a garlic flavour in the beer.
Mr. Rühl, in reply, said, with regard to aeration, Continental brewers were far from holding the same opinion on this subject. Aeration must be carefully carried out, and not beyond a certain point. Explaining why, on the Continent, yeast was washed, and emphasising that this was done mainly in order to remove small cells at the same time, he reminded them that in lager beer breweries infection was not the small matter that many of them might be inclined to think, and they must not forget that lager beer brewers were not allowed to use preservatives of any kind, and the low temperature was not alone sufficient to prevent the beer being affected. Although there were instances of paraffin wax being used on the Continent, perhaps on a large scale—for they had to keep large stocks of small casks—pitch was more largely used. Personally, he had not had any experience of the treatment by paraffin wax.
Mr. Beech mentioned that he treated his casks quite successfully with cold water.
Dr. A. K. Miller, in reply to Mr. Richards, said he (Mr. Richards) would find an account of the researches to which Mr. Rühl had referred in a paper by Dr. Ehrlich published in the Year Book of the Berlin Institute of Brewing for 1907.
The meeting concluded with a hearty vote of thanks being accorded to Mr. Rühl, on the motion of Mr. Morris, seconded by Mr. R. Whitaker.