Studies On Stouts

ON FRIDAY, MAY 1st, 1908.

Mr. Thomas Hyde in the Chair.
The following paper was read and discussed :—

Studies on Stout.

By Norbert Van Laer and James D. Wilson.

Part I.

In discussing with medical men the properties of stout as compared with ale, it is interesting to follow the varying hypotheses put forward as solutions of the problem. It is a matter of common knowledge that doctors differ in their opinions, and in our experience we have met the same with brewers. If we enter into argument with the brewer concerning the question under consideration, we find ourselves confronted with various hypothetical views.

We have made a small attempt to investigate the obscure and complicated reasons why medical men, in many instances, recommend stout in preference to ale to their patients requiring stimulants. We have frequently been told that ale did not agree with some people, but that stout proved most beneficial. On the other hand, we have heard objections to stout on the grounds that it was too heavy, and for other reasons not worth mentioning.

At first sight this appears to be somewhat at variance with general supposition, and especially so with established ideas of the brewer. In order to ascertain for ourselves, however, we have undertaken a certain amount of chemical and bacteriological work which is not yet completed, but we anticipate at some future date to be able to furnish further data.

We commenced our investigations with some chemical analyses directly related to brewing, reserving the estimation of volatile by-products for some future occasion. As a basis, we have taken a Dublin stout. The samples for analysis wore obtained direct from the bottler and guaranteed to be genuine. At the time that the analyses were made, the stout had boon in bottle one month.

The following are the results of the analyses:—

Although we aimed at obtaining an ale free from sugar, and of exactly the same original gravity as the stout, we were disappointed in having a difference in the latter, which, nevertheless, is close enough to demonstrate the variation existing between the stout and ale from a purely chemical point of view. Having no particulars concerning the brewing of this particular stout, we do not wish to enter into details regarding its chemical constituents. Doubtless the low attenuation and lengthy storage, or the blending with well-matured stocks, would be the best explanation to offer.

As another comparison, we obtained a stout of a gravity approaching the Dublin stout and the ale, also free from sugar, which on analysis gave the following results:—

On looking through the results of the analysis of the Dublin stout, and comparing the figures with the all-malt stout and ale, it is interesting to note that the Dublin stout has a chemical composition notably different to the other stout.

Desiring to carry out our investigations further, we carried out a number of analyses of several noted stouts from different parts of the country, and compared them with ales of, as near as possible, corresponding gravities. These are rather too numerous to be dealt with fully here; we have, nevertheless, made a selection of a few, and without entering into their direct origin, we will designate them numerically as under:—

We have not made the complete analysis, as we were unable to obtain sufficient information concerning the brewing, and whether any sugar had been used, this latter factor being of great importance in the guidance of the detailed analysis.

In studying the chemical comparison of the stouts and ales, it is interesting to observe the slight difference existing between some of thorn, which is not sufficient to attribute any superior properties to the stout over the ale when of the same gravities and stored under similar conditions. One point in which we are particularly interested for the present is the higher acidity of some stouts over ales. In the majority of Stouts recommended by physicians, we observed high acidity, and the highest fixed acidities were found in the most popular stouts.

In Stout No. 1 (Dublin) and No. 4 (London) it will be observed that the total and fixed acidities are higher than in the others, and in comparing them with ales of almost the same gravities, a very marked difference is apparent. These two stouts, varying as they do in original gravity and other constituents, contain very nearly the same acidity.

The chief point of interest in conjunction with what we have said regarding Stouts Nos. 1 and 4 was the similarity in the microscopical examinations, before and after forcing. Without entering into the question of secondary and wild yeasts, the presence of two species of bacteria of a short rod form was always associated with the Saccharobacillus Pastorianus (Van Laer).

Although we have found this in most of the stouts under examination, in Stouts Nos. 1 and 4, where the percentage of alcohol had approached 7 per cent, there was no appreciable increase in fixed acidity after lengthy storage. In addition to the stouts referred to, we have microscopically examined a number of others, and with the exception of Nos. 6, 7, and 8 of Burton brewing, we have found the Saccharobacillus Pastorianus forms.

The preceding tables show that the percentage of alcohol in the stouts exceeded the proportion considered to be of retarding action to the lactic acid producing organisms. In some other stouts we have examined there was a great variation in the total acidity on storage, and more especially on forcing, this especially in some stouts of low alcohol percentage, high in nitrogenous matter, and a low hop rate.

Wo are, therefore, forced to the conclusion that the organisms producing the acidity in some of the stouts are of different species to those found in Nos. 1 and 4.

Returning to the presence of the Saccharobacillus Pastorianus forms, the following description of some experiments may, perhaps, be of interest:—

Twelve experimental mashes wore made under identical conditions, six of which contained pale English malt alone, and the remaining six 80 per cent, of pale English malt and 20 per cent, of black malt. The wort contained was treated in six different methods in order to ascertain what influence hopping, boiling and fermenting had on the pale malt wort alone, and on the wort containing 20-per-cent. black malt. The following were the conditions adhered to in the experiments.

Mashing.—175 grams of pale English malt were used in six of the experiments, and 140 grams pale English malt with an admixture of 35 grams black malt in the second six series. These were mashed at an initial heat of 156° F. for one hour and a-half, filtered whilst hot, and the grains washed with distilled water at 180° F.:—

1. The pale English malt wort was hopped at the rate of 2 lb. per barrel (best Kent), boiled for one hour, water being added from time to time to prevent over-concentration. Filtered after boiling into a sterile flask, the heat being again raised after filtration to boiling to ensure sterility; cooled under aseptic conditions and pitched with a pure culture of yeast. The pitching gravities in the experiments ranged from 1068 to 1072.

2. The black malt wort was treated in precisely the same manner as No. 1, being hopped pro ratum 2 lb. per barrel.

3. Pale malt wort same as No. 1, but hopped 3 1b. per barrel.

4. Black malt wort as No. 2, but hopped pro ratum 3 lb. per barrel.

5. Pale malt wort. The process same as No. 1 without the addition of any hops.

6. Black malt wort. The process as No. 5, also unhopped.

7. Pale malt wort, neither boiled nor hopped, filtered hot after mashing under sterile conditions (sterile funnel, filter paper, flasks, etc.), the wort on filtering being covered over, cooled and pitched with a pure culture of yeast.

8. Black malt wort, process same as No. 7.

9. Pale malt wort, mashed and boiled in usual manner, no hops being added and no yeast.

10. Black malt wort, same as No. 9.

11. Pale malt wort, same as No. 9, but hopped pro ratum 2 lb. per barrel.

12. Black malt wort as No. 11, hops being added pro ratum 2 lb. per barrel.

These flasks were left at ordinary laboratory temperature for a fortnight and then microscopically examined. At the time, there were slight signs of bacterial growths in Nos. 2, 6, and 8; about one rod form in four or five fields. The flasks were examined again at the expiration of the third week from the beginning of the experiments, when there appeared to be no bacterial development in any of the flasks with the exception of Nos. 2, 6, and 8, in which the increase was very slight. On placing the flasks upon the forcing tray and maintaining them at 21 per cent, after 24 hours these were again examined, and this continued during 15 days’ forcing.

All the samples brewed with pale English malt remained pure during the whole of the forcing period, whilst No. 2, brewed with the addition of 20 per cent, of black malt, showed an increase in bacteria of the Saccharobacillus Pastorianus form, averaging about six per field. In sample No. 4, hopped at the rate of 3 lb. per barrel, no bacterial development had taken place during the first 15 days of forcing. Sample No. 6 contained the Saccharobacillus Pastorianus to the amount of three per field. The microscopical examination of No. 8 was practically the same as No. 6. Samples Nos. 10 and 12, both unfermented, No. 10 unhopped, and No. 12 hopped at the rate of 2 lb. per barrel, showed no signs of bacterial growths.

It is our intention to repeat these experiments with black malts, freshly roasted, and others of some lengthy storage. In our next communication we hope to be able to bring forward the results of these experiments.

By the absence of the Saccharobacillus Pastorianus in all the pale English malt experiments, and judging from its presence in Samples Nos. 2, 6, and 8, we are inclined to attribute its introduction to the black malt. The slackness of some black malts and their charcoal character doubtless render the same an absorbent of micro-organisms when exposed to the air, which fact may perhaps account for the presence of the Saccharobacillus Pastorianus in some black beers. That the boiling does not destroy the spores of this organism is conclusive by its appearance in the samples referred to in the experiments.

With regard to the anomaly of Sample No. 4, this may probably be accounted for by the additional pound of hops, which seems to have a marked influence in checking the reproduction of the Saccharobacillus Pastorianus.

The determinations of the alcohol produced in the samples of the first eight malt experiments after two months was as follows:—

The percentages of alcohol in Samples Nos. 2 and 6 were the lowest of all, hence more growth of Saccharobacillus Pastorianus. The higher percentage of alcohol in No. 8 would, to a certain extent, explain the similarity existing between Nos. 6 and 8 with regard to the microscopical examination.  During our investigations we have found that the presence of Saccharobacillus Pastorianus was most apparent in stouts in which the assimilable nitrogen was the highest. That the question of assimilable nitrogen is of considerable importance in relation to the development of the Saccharobacillus Pastoriauns has been previously demonstrated by the valuable researches of Dr. Horace T. Brown. In his very instructive paper on “The Nitrogen Question in Brewing” (this Journal, 1907, 13, 440) Dr. H. T. Brown says:—

“There is no necessary connection between the attenuation limit and the removal of the assimilable nitrogen; by which I mean, that it is quite possible to run the attenuation down to a low point and still retain a dangerous excess of assimilable nitrogen in the beer. The conditions which are most effective in restraining this excess are antecedent to the final stages of fermentation, some of them, in fact, depending on the choice of the materials themselves. In this aspect of the nitrogen question, we have a rational explanation of the modern brewing practice, founded on experience only, of using a reasonable amount of brewing sugar and an admixture of such foreign malts as are comparatively poor in solution nitrogen. In this way the brewer dilutes the total and assimilable nitrogen in his worts and, other things being equal, in his beers also.”

Suffice it for us to apply the above remarks to explain the circumstances favouring the development of the Saccharobacillus Pastorianus, so often met with in stouts. The troubles caused in ales by this organism are too well known to require mention here, but in stouts, the cloudiness it produces is masked by the intense colonr. The acidity produced impairs its stability, and this is more pronounced in some brewings of stouts, and is probably owing to the assimilable nitrogen being higher and the medium more adapted for the re production of the organism.

In our microscopical examinations, we have found, especially in some stouts, the presence of a large number of short rod forms which, on isolation in pure culture, proved to be of a lactic type; these predominating in several of the stouts examined. These stouts on lengthy storage and forcing wore not in the least impaired in stability.

It is a general belief amongst brewers that microbes are all disease producing organisms. The eminent scientist, Professor Metchnikoff, a name, which is of course very familiar to you all, in one of his latest contributions “The Prolongation of Life: Optimistic Studies.” Elie Metchnikoff, on p. 181, says:—

“A reader who has little knowledge of such matters may be surprised by my recommendation to absorb large quantities of microbes, as the general belief is that microbes are all harmful. This belief, however, is erroneous. There are many useful microbes, amongst which the lactic bacilli have an honourable place.”

In applying this statement to our investigations on stout, we beg to point out that the lactic acid ferment met with in stout is of a totally different species to that discovered by Professor Metchnikoff. Pasteur, in 1857, demonstrated that this organism could produce lactic acid although its action was interfered with by an excess of the acid. When the action of the lactic acid is continued too long, it not only arrests the process of fermentation, but definitely kills the microbe. When we drew your attention to some noted stouts, containing a large number of organisms of the lactic type, the acidity was only slightly changed after several months’ forcing. This would explain the reason why the lactic acid ferment does not exist long in a living condition. In milk the longevity of the lactic ferment of Metchnikoff remains unaltered for a considerable period. We have here a pure culture of this ferment that was regenerated from n culture we have had for nearly six months. As you can see, the lactic fermentation is in full action. It would necessitate departing too far from the subject of this paper to enter fully into the nature of this interesting discovery.

The following abstract of Metchnikoffs work may be of interest with reference to the culture of lactic ferment we have here :—

“After the milk has been boiled and rapidly cooled, pure cultures of the lactic microbes are sown in it, in sufficient quantities to prevent the germination of spores already in the milk and not destroyed in the process of boiling. The fermentation lasts a number of hours, varying according to the temperature, and finally produces a sour, curdled milk, pleasant to the taste, and active in preventing intestinal putrefaction. This milk, taken daily in quantities of from 300 to 500 c.c, controls the action of the intestines and stimulates the kidneys favourably. It can therefore be recommended in many cases of disorder of the digestive apparatus, of the kidneys, and in several skin diseases.”

The problem before us now is whether the presence of the lactic ferment in stout does not play an important part in this interesting subject. Before concluding, may we say that this communication only applies to bottled stout. In our next contribution, we hope to be in a position to bring forward some more conclusive evidence.


The Chairman, after remarking that the paper had been most interesting, inquired whether the authors attributed the difference between stouts and beers of practically the same gravities to the black malt extract, or caramelised materials used in the former. It occurred to him that the ropiness in bottled stout that had given trouble at several breweries might probably be due in some measure to the lactic acid, which was shown to occur more in stout than in beer. That idea had been somewhat strengthened by the example shown by Mr. Van Laer of the way lactic ferments affected milk—converting it to a jelly-like substance. It was rather remarkable that brewers were hardly ever troubled with ropy beers, although most of them, no doubt, had had some experience of ropiness in stouts.

Mr. Van Laer said that in speaking of ales as compared with stouts of approximately the same gravities, they had met with vast differences in the case of some stouts, both as regards the chemical composition and also the microscopical examinations of the sediments. They would not like to say that this was due to the black malt or caramelised materials. Although they were of the opinion that the black malt, if slack and used in fairly large proportions, had been the means of introducing bacterial contamination, especially with reference to the experiments on black malt they had dealt with. Concerning the remark of ropiness in bottled stout, they quite agreed that bottled stout was more liable to ropiness than bottled ales. But in this case the ropiness was due to ropy ferments which produced a large amount of acidity. This acidity was totally different from that produced by the organisms referred to in the paper. Therefore, they would like to impress that the ropy ferment, which was the greatest enemy of the brewer, should not be confused with the lactic ferment or the acidity produced by these organisms. Ropy ales were now of very rare occurrence, especially in the trade, whilst ropy stouts were often encountered at certain times of the year.

Mr. C. F. Hyde referred to the percentage of acidity in London and Dublin stouts, and observed that the percentage was higher in the case of the Dublin stouts. He made a visit some 14 years ago to a Dublin brewery, and what impressed him were the huge oak fermenting vessels of a capacity of about 1000 to 1500 hogsheads. He was puzzled to know how these vats could be cleaned before the wort was run in, as he was given to understand they never scalded them, and he regarded them as being a very good field in which to cultivate Bacterium aceti. He had no doubt that a large amount of acidity had its source in this way. It was then carried forward to the vats, and increased during the vatting process. That would account for the high percentage of acidity as compared with a London stout. He understood the authors that, on the basis of Dr. Brown’s experiments, if the percentage of assimilable nitrogen was high, it gave a  correspondingly high acidity in a stout.

Mr. Van Laer said that in the large number of stouts they had examined, the Dublin stout had the highest acidity, but they had obtained one of a London brewery of which the acidity was nearly similar. Mr. Hyde’s description of what he had seen in Dublin was interesting, and from what they gathered they were of the same opinion that under the conditions stated it would form an excellent field to propagate various species of organisms. They understood that the vatting of stout in London had almost entirely died out. Concerning the references made to Dr. Brown’s experiments on the influence of assimilable nitrogen, they would like to say that they had not at present proved a direct relationship between the percentage of acidity and excess of assimilable nitrogen. They had already recognised the importance of this question, and hoped to make investigations.

Mr. C. F. Hyde said that in his opinion the assimilable nitrogen, especially in Dublin malts, was extremely low, and he could not reconcile the high percentage of acidity as being attributable to that source. On looking at a sample of a Dublin pitching yeast, he was struck by its poor, starved, and granulated appearance. If they had a malt wort, or a malt that would yield a wort with a fair amount of assimilable nitrogen, he did not think that that would obtain. His experience was that high-dried malts always gave a poor, starved granulated kind of yeast; high drying on the kilns had its result in a low assimilable nitrogen in the wort.

Mr. Van Laer said that with reference to the assimilable nitrogen being low in Dublin malts, they did not think there was sufficient evidence at present to support that statement. He was somewhat out of touch with the microscopical examination of Dublin pitching yeast, and would, therefore, abstain from making reference to that subject. They agreed with him as regards his statement about high-dried malts.

Mr. Richards asked if they were to understand that the higher the amount of nitrogenous matter the higher the acidity.

Mr. Wilson said that they had found from their investigations that the composition of stout, especially in some of which the chemical constituents were known to them, the medium seemed most adapted to the development of certain species of acid-producing bacteria, principally the Saccharobacillus Pastorianus, which was present to a large extent in stouts when the nitrogen was in excess.

Mr. J. G. Wells said that the authors rather seemed to advocate the presence of Saccharobacillus Pastorianus us being an improvement to the stout.

Mr. Van Laer said that it was erroneous to assume that they advocated the presence of the Saccharobacillus Pastorianus as being an improvement to the stout. What they wished to point out was that they had found this organism in the sediments of some noted stouts, which, on forcing for about one month, exhibited a very large number of these organisms. On taking the acidity before and after forcing, the acidity, especially of two samples examined, only showed a slight increase, not to any degree corresponding with the growth. On the other hand, they had found its development greatly arrested when the amount of alcohol bad exceeded 7 per cent, and subject to absence of oxygen.

Mr. Wells asked if the authors attributed the contamination to the black malt.

Mr. Van Laer said that there were many factors to be considered before he could give a definite reply to such statement. For example, a black malt might have been produced from unsound barleys and the malting process carried on under very unsatisfactory conditions. Moreover, barleys of inferior quality could be made into black malts. Then, again, black malt was very subject to slackness if kept for a length of time. In concluding, they would say that, from their experience, black malt had boon the source of introducing bacterial contamination.

Mr. Wells remarked that the wort had been boiled.

Mr. Van Laer said that in their experiments they had boiled the worts for one hour, and this had not killed the spores of the Saccharobacillus Pastorianus, as their presence was observed in the samples Nos. 2, 6, 8, as previously referred to, re their black malt experiments.

Mr. Wells said that the late Dr. Morris and himself had proved some years ago that under brewing conditions the wort was sterile after boiling.

Mr. Van Laer said they had given special attention to this important subject of sterilisation, and, from various experiments undertaken, they would state that they were of diverse opinion. In reply to a question by Dr. Miller, Mr. Van Laer said that the presence of the lactic ferment might, in some noted stouts, possess certain characteristic properties which the brewer was aware of, and therefore did not try to avoid this organism, but he did not wish to state this definitely until they had pursued their investigations further.

Mr. C. F. Hyde inquired whether the author, in examining the popular stouts referred to after being in bottle or in cask for some time, had found anything besides the Sacchrobaccillus Pastorianus and lactic ferments.

Mr. Van Laer said that referring only to the types of stouts mentioned by Mr. Hyde, they had, of course, in addition to the Saccharomyces Cerevisiae, found species of secondary yeasts, sometimes wild yeast, together with a preponderance of other organisms.

Mr. G. Jones asked if the authors had any analyses available of black or coloured malts in respect to nitrogenous matter.

Mr. Wilson said that they had not any figures directly bearing on the nitrogenous matter in black or coloured malts, but they could say that the percentage in black malt was very small.

Mr. Jones said that from what Mr. Hyde had said, and from his own experience, the amount of nitrogenous matter in a coloured malt was less than in a pale malt. How would the authors account then for the increase of nitrogenous matter in stout as shown in the specimen analyses?

Mr. Wilson suggested that the materials might not have been so carefully selected. Very often coarse malts were used for stouts, as a bright article had not to be produced. Many of these malts contained a higher percentage of nitrogen than the more carefully selected, used in pale ales. They were inclined to attribute the higher nitrogen in some stouts somewhat to the fact that they wore never, or seldom, fined artificially.

Mr. Wells said that they used in a stout brew as good a pale malt as in an ale brew. The only difference was in the coloured malt, the proportion of which was not large.

Mr. Wilson said that in Mr. Wells’ case, where practically the same malts were used for ales and stouts, he could only attribute the higher nitrogen in the stouts to the fact that they were probably not fined, or, again, in many stout fermentations there would be a smaller assimilation of nitrogen by the yeast than in ale fermentations, owing to different mashing conditions, hop rate, etc., which would leave more nitrogen in the stout at racking.

Mr. Wells said that he was speaking generally that in stout malt they did not get a very big percentage of coloured malt. But it had always been his experience that stout was peculiarly susceptible to disease. He remembered a brewery that at one time suffered a good deal from ropiness, and nothing was more susceptible to this than the stouts. Could the authors explain why stout was so peculiarly liable to contamination?

Mr. Van Laer said that the percentage of coloured malt and black malt varied a great deal in some stouts, and the more so according to whether caramel was used. It was a noticeable fact that black beers had a greater tendency to ropiness than ales. It was generally believed that the bacterial contamination was introduced through the employment of unsound, forced malts, and particularly those which had been undercured, also slack malts. Insufficient hops, impurity or weakness of the pitching yeast, and excess of assimilable nitrogen would tend to explain why stout was so liable to contamination. In reply to Mr. Morris, there was one type of lactic ferment known which possessed medicinal properties, and that had been demonstrated by Professor Metchnikoff and other authorities. Naturally the lactic ferments of stout were of an entirely different species, and for the present this was a problem open for further investigation. He would, nevertheless, say that if a stout possessing a certain acidity, remaining fairly constant, and not impaired in stability, was appreciated by the public, he thought it advisable to continue on the same lines. In addition, they would draw their attention to the fact that it was essential to know the chemical constituents of the stout and the character of each organism present, before giving a decision upon this matter.

Mr. A. E. Taylor said that he was distinctly of opinion that the increased percentage of lactic acid in stout was appreciated by the public, and therefore it should be the aim of the brewers to keep this fact in view.

Mr. Van Laer said that although some noted stouts contained a high percentage of lactic acid, they did not wish to impress upon them that they attributed the superior qualities of some of these stouts to the presence of lactic acid only, as doubtless the question of volatile by-products had to be considered, and in their opinion this latter factor was of great importance. They anticipated undertaking soon some work on the volatile by-products.

Mr. A. E. Taylor said that the best quality of vinegar was found to be that which contained the largest quantity of lactic acid produced from the lactic ferments, and vinegar prepared from all limit wort achieved this. On comparing an all malt vinegar with a vinegar brewed largely from sugar, the inferior quality of the latter was distinctly marked.

Mr. Van Laer said that he had been much interested in Mr. Taylor’s remarks, and would like to enquire whether this statement applied to any special type of lactic acid organism, on which Mr. Taylor could give them further information.

Mr. Taylor said that what he had stated was based on his own observations in the commercial manufacture of vinegar. He was not acquainted with any special research on the matter. He had pleasure in moving a hearty vote of thanks to the authors of the paper. The subject they had drawn attention to was one of great interest, and he felt sure that the members could profit greatly by bearing in mind the information they had just received, when producing their stouts.

There was to-day and he thought there had always been, the greatest opportunity for brewers to develop a remunerative and increasing trade in stout, more particularly than beer; why stout should lend itself more readily to a development of trade than beer he could not say, but would venture to attribute it to the greater range in character or palate flavor which could be aimed at in stout brewing. He was very interested to hear what had boon said about the lactic ferments. He was aware that these ferments were receiving the attention of the medical authorities as to their curative treatment of internal wasting diseases, and as they had just hoard, those stouts which secured the highest esteem of the medical authorities on analysis were found to be richest in these lactic ferments. As regards black malt, he had seen it stated that it was an antiseptic, but he had always found it the cause of excessive fermentation, and he believed that lactic ferments were derived more or less from this source. As to the cause of ropiness in stout, he certainly should not attribute this to the use of black or brown malts, but suspected it arose from the sugar or caramels that had been used in the production of such stout. The Society had already listened to a paper recently at which it was demonstrated that where ropiness existed in a beer, potassium salts were also present. A guaranteed pure cane-sugar should, therefore, only be used, and this should apply to all invert sugars and black caramels. He did not object to any of the above syrups containing a portion of glucose, but what he took the strongest exception to was the mixing of beet sugars with such preparations, as beet sugars were frequently found to contain traces of potassium salts.

Mr. J. G. Wells seconded the vote of thanks.

The resolution was carried unanimously, and briefly acknowledged by Mr. Van Laer.

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