Practical Notes on the Stone Square


The following paper was read and discussed:—

Practical Notes on the Stone Square System.

By Otto Overbeck, F.C.S., RG.S.

In the stone square system we have to deal with a variety of yeast of a hardy nature, capable of withstanding much rough usage and requiring a great deal of mechanical movement during all but the initial stages of fermentation in order to preserve it in health and to bring the results to a satisfactory conclusion as regards the character of the beer; further, to obviate any weakening or falling off of the yeast organism in reproductive capacity, so that a healthy crop for pitching succeeding gyles is secured.  The vessels used are of a far more cleanly character in regard to contamination with foreign organisms than are those employed in other systems, being constructed of stone or slate, which are much less porous than wood.  The sides or walls of what pores do exist (superficially) are not permeated by the wort, and this cannot be said of wooden vessels.  In common with wood these vessels are, however, subject to the deposition of scale from the wort, consisting of calcium oxalate; but this is easily removable by a wash of chloride of lime with or without gentle scrubbing; this latter is harmful to all wooden surfaces.  The effect upon this scale of a solution of chloride of lime is to gradually decompose it into carbonate of lime in the form of a fine non-adherent precipitate which washes off readily with the hose.  Of materials generally used, stone is the toughest and hardest, but on the other hand it is the heaviest and clumsiest to move.  This limits the size of the squares, and those of 30 barrel capacity are difficult to obtain.  False bedding should be avoided, the character and hardness of the stone varying in it from layer to layer.  Where the vessel is possessed of a similar shell, its conductivity or heat-conveying power is comparatively small, and it will stand no sudden fluctuations safely.  The consequence is that either in warming during the early stages of fermentation or cooling in the later, much water is used, which in summer in certain districts with limited cooling powers for the wort coming from the coppers is a serious consideration.  I believe such to be the case in Sheffield at the present time.  Some of these drawbacks may be obviated by using the lighter and thinner slate squares.  The surface of slate is very smooth, its conductivity better than stone, but its brittleness and tenderness are a drawback.  This latter defect is most frequently experienced from a blow, which can, however (excluding accidents), be obviated at the lower edges where most exposed, by raising the bottom of the vessels above the height of the top of the yeast tuba.  This offers ample air-circulating space below and prevents the great drawback of having S-shaped drawing-off taps which are more difficult to clean: a point to note in the erection of any new or alteration of any old standing vessels.  The spacing of the vessels from each other and the walls of the building must also be taken into account.  Of whatever material the vessel may be made, let it not be supported by pillars of brick, which are invariably a source of contamination, and are also so easily cut up by the yeast tubs.  Let them be supported entirely by iron pillars and closed box girders, which, with aluminium paint, always look well and, moreover, show at once upon their bright surface any film of whatever kind it may be. It should also be borne in mind that the surface of the base stone ought not be raised above, but level with the ground.  Wood, copper-lined, has been tried with only partial success, for the outer or shell vessel, with metallic square within.  It is, however, most difficult to locate or to mend a leak; decomposition and contamination resulting if not attended to at once.  Iron-jacketed vessels with a non-conducting covering are also unsatisfactory.  The new wired glass should prove excellent, provided the metal be absolutely enclosed and air-tight, or else from oxidation and resulting expansion the vessel may collapse.  I fail to see why plain annealed glass should not be used with free metal attemperators within standing on feet and discharging over the top; in this case no shells would be required.  Washing would then be a simple operation, the only consideration being the joints which, with a little roughening and special corner pillars, should prove quite simple.  A ratio of surface in the top-back as compared with the capacity of the lower vessel seems never to have been properly established.  This is a matter of difficulty, since there is a constant variation in yeast, however gradual it may be in each successive brew.

From on experience extending over a number of years, I am of opinion that very large shallow backs yield outputs of yeast rather sooner than small ones; the beer clarifies quickly, but in the early stages the largely exposed heads are tender.  It is, however, a moot point.  Where shells are in existence, the overlapping of the top stone forms a good protection against foulness from yeast dripping into the intervening spaces, but affects its cleansing possibilities adversely.  If there is an ample supply of water at the requisite temperature, squares are best without shells, a removable coil taking their place.  In such cases an electric bell thermometer is useful to limit heats; and it can be set to any temperature, thus warning the men of heats dangerous to yeast.  In some breweries it is quite possible, besides utilising the heat of the cooling wort, by pumping the refrigerating water either to the hot liquor or barrel washing tank, to use this in part to supply the square shells with warm water.  Heating and cooling must be gradual: in the first place on account of the yeast, and in the second that of the beers; we can so easily cripple the former, rendering the beer bitter and hazy.

When shells overlap, and jelly collects in summer, caustic soda, with permanganate of potassium, will both oxidise foul gases, and sterilise, and at the same time dissolve the jelly.

Regularity of process is important, and, as brewers, we ought to be in a position to know at all times what has taken place with our wort, hence in large breweries machinery takes the place of hand pumping and rousing; with most satisfactory results, especially when automatic and self-registering by day and night.  So little is required to upset a yeast, and its product as a consequence, that a healthy yeast is synonymous with good beer, and no materials, be they what they may, will give a good beer if pitched with a weak yeast until so many generations have passed that the yeast has again become strong.  That indistinct, washy taste has little to do with the wort, but everything with the yeast.

In the stone square system we labour under one disadvantage, namely, that we cannot choose our pitching heads so well as in the round system, owing to the pumping and rousing.  Yeast should be at once cooled on collecting, but for this purpose a cold water stationary coil should be replaced by a movable one; exposing large surfaces to the air is unwise. In the height of summer yeast becomes far thinner; this is largely due to increased solubility at the higher temperature of the cell contents, with correspondingly enhanced osmosis.  It is extraordinary, however, how sometimes a pitching of yeast will suddenly collapse, and how difficult it is to give any just reason for it.  I note especially one such case this year where the yeast from the beer was everything that could be wished, but when stirred the next morning practically collapsed to nothing.  Remember that in yeast there exist considerable inter-cellular spaces, so when collapse takes place throughout the mass it is at once apparent.  It is no disappearance of substance or matter when yeast undergoes such a diminution in volume, and I would ask you to remember that, similarly, shot as such, and after being melted down, occupy very different volumes.

Should our yeast deteriorate bacterially, it may happen in two ways —

  • contamination by bacteria far smaller than itself, such as acetic, lactic, butyric, ropy ferment; and
  • by wild yeasts, such as the Pastorianus species, which cause haziness and ill flavours.

The former can be pretty completely removed by means of fresh wort and a filter table, Excise permission being necessary to use wort for this purpose.  In the latter case we have to turn to other methods, such as preservatives, foreign malts, etc.  I know of nothing worse than when such germs are prevalent, filling the brewing premises and its air with their spores.  Bacteria, like all other plants, have their good and bad seasons, and, considering their size, it is of course very difficult to either locate their field of growth or say what may or may not be a good season for them.  This we know, that one which is damp, followed by a period of drought and heat, is the worst for us; an entirely damp season seems to hinder sporulation.  Hence the year preceding was bad for them and good for us.  This present year has been a good one on account of the continuous long drought, beginning early on and crippling spring growth.  In some summers the air seems in certain parts to teem with Saccharomyces Pastorianus, so that even if we keep our beer free, the interior of the barrels become covered with spores, to the certain detriment of the beer, nearly every cask developing that silky growing haze.  At such times there is but one remedy I know of—a wine-glass-full of sulphurous acid in every barrel to be racked, to stand overnight.

One advantage must undeniably be accorded to the stone square system, and that is, maximum body for any given gravity, and the highest possible finals, this being especially marked in a quick draught trade.  It is often the saving factor in overcoming competition against beers of the same original gravity browed otherwise.  It is unwise to rack single squares, since in one brew of many squares no two single squares turn out exactly alike.  Everything should be done to produce a reliable uniformity, which is the secret of success.  Similarly, the back drinks should be blended into the brew and not unduly exposed to the air, being collected preferably in cast-iron vessels, with the flanges cemented outside to a slope, to obviate ledges for growths.  We may blend beers in a racking tank to improve the total output, yet spoil all by having to rack before a sufficient amount of stirred-up yeast has had time to settle.  This is very unfortunate, especially in summer, for it means excessive yeast under conditions of heat most liable to make it kick up, if Pastorianus be present, inviting haze.  I would also utter a warning against hurriedly cooling beer, at times of good trade, on account of lack of time.  A few extra hops are useful to moderate immediate fiery after-fermentation in the publican’s cellar.  I fear that the few extra hops will not be forthcoming next year; however, preservatives have the same effect, and in this connection let me add that Nature, which does not always follow man’s ideas, has declared for salicylic acid, since this has boon found as a regular constituent of the juice of some fruits, especially raspberries and strawberries (whose juices ferment so freely), Nature making each fruit its own little barrel plus a little dose of this much-maligned preservative, whilst formaldehyde, oxidised into formic acid, is the natural preservative of honey.  This substance, however, is destroyed by ammonia and combines with peptones to form insoluble substances, and this should be borne in mind in its use.

Economy, the one word which spells dividend nowadays, is an all-powerful factor in the brewery, and may be either wisely or very unwisely employed.  Any economy which limits definite profitable improvements is a hindrance, since a trade depends solely on the class of its output to maintain its existence.  No saving can be effected without a temporary outlay of capital; it is in this sense that I refer to such savings as the following:—utilising grains by some process of preserving them when there is a glut in the market.  There exist several drying machines for largo concerns, or they may be pressed down and salted in old barrels and blended during the winter months.  The sediment from the backs can be dried atmospherically, and the clear beer run off, and the same applies to the sludge of stout and beer on the coolers ; the latter saves a lot of trouble in putting up to stand, etc., and the product is far better.  The pulse of a stone square brewery is undoubtedly the fermentation, and it is a subject for discussion as to how often and how long a period in any particular brewing it is best to rouse, and how much pumping should take place.  Why should one room always be ahead of others?  Why should some squares start prematurely with a frothy head, yet all finish together?  Why will a brew of one wort, similarly treated and pitched, stop at various points in different squares?  Why should one sot of squares yield more yeast than another?  These are points of intense interest, and, perhaps, to a certain extent, a reply to the capacity of the backs.  Again, how far wort spreaders below the pumps are advantages or disadvantages.

With a clockwork method of brewing, as in the stone square system, we can observe yeast action far better than in rounds, for our process is more fixed and unalterable.  We can see at once how a new blend of malts affects fermentation, and how often we have to bless the fact that we have several malt kilns yielding varied types of malt, to give that variety without which yeast in the long run invariably deteriorates.  The day for picking-up a yeast upon an all-malt brew is gone, I believe, entirely, and now that chemistry points to lactic acid as being the half-way product of fermentation between the hexoses, such as glucose and levulose and alcohol, its presence (larger in all-malt brews) acquires a perfectly new importance, and may prove the yeast thermometer of the future, and enable us to differentiate two actions—that of zymase and some other enzyme. Let me incidentally refer to arsenic as I did when speaking of cleaners on a former occasion.  I will agree that it is more expensive, but no analysis has any value to a brewer which does not express a figure limit; such phrases as “trace”, etc., being, under present conditions, too vague, unless distinctly stated to be below such limit.  One other word on this head.  We know that the light dust, which is highly arsenical, although small in quantity, is actually carried away from the malt, and this being so, we must take precautions that it be not deposited elsewhere in the brewery.  From light dust, 70—80 feet away from a dusty cleaner, it is quite easy to get a mirror of arsenic heavier than from dust taken nearer to the machine.  Let me here supplement these notes by some remarks referring to parts of plant, which may prove useful.  All mains are best in jointed lengths; the in and out wort services should be distinct to avoid the necessity of hasty racking, and the former should be laid over the squares.  The pipes leading from the shells should pass straight into a horizontal water exit service direct to the drains.  This saves scrubbing slime from the conduits in summer, and obviates damp through splashing.  Drains conduce much, indirectly, to yeast impurity, and an acid-smelling fermenting room; no growths can take place on a dry surface.  Large amounts of aerial germs and dirt are excluded from the yeast by means of fine (preferably silk) muslin stretched across the casings of the windows, the doors being kept shut in the yeast room.  It is astonishing how soon these require renewal by simply collections of aerial filth, especially in large towns.  The yeast room should always be kept closed from atmospheric contamination by draught, and is best lined with glazed bricks.  Pumps should always have a draining tap, and the supervision of these, and the other parts of the pumping and rousing system, require frequent examination, especially in searching over porous or impure rousers.  Pumping and rousing are very light works, and should, wherever possible, be done simultaneously, saving labour, and not impairing the uniformity of the beers.  In towns with an electric supply such work can be done automatically with great ease.


The Chairman, in inviting discussion, said they had listened to a practical and interesting paper on a subject which especially appealed to the members of the section, as men working on the Yorkshire system of brewing, and he hoped to hear some further remarks on the subject.

Mr. H. M. Chubb asked the author if there was any given limit to the size of a stone square, and what size the manhole should be in proportion to the size of the square.  Would Mr. Overbeck consider a square of 120 barrels capacity too large?  He believed the most general size was from 25—30 barrels.  He would also like to ask Mr. Overbeck what was the best method of cleaning malt, and what percentage of arsenic could be got rid of in the process?  Would it be possible to reduce a malt containing 1/150 of a grain per 1b. to 1/300 of a grain per lb. by cleaning?

Mr. W. O’Connor said that with stone squares one of the difficulties was in connection with blisters, which developed in the flaws existing in all but the best stones, and necessitated continual chipping and smoothing, ultimately leaving an uneven surface, difficult to clean.  For slabs he considered slate a superior material, being harder, smoother, and freer from these germ-traps.  With slate squares as a cure for slight leakages or inequalities in the joints, he had found the use of soft white metal far superior to cement, as not being of so brittle a nature, it was not knocked out by the scrubbing brushes during cleansing.  He would ask Mr. Overbeck what cement he most approved of as setting for the joints of the stone.  Ho could not see what objections could be raised to the use of cast iron for squares, of which material Mr. Overbeck approved for hop backs, and which, if properly treated with tannic acid, would not develop rust, and, on account of its conductivity, would leave considerable power in the hands of the brewer to correct temperatures by means of the waterjacket.  The speaker confirmed Mr. Overbeck’s views regarding the insufficiency of the present styles of brushing to completely remove arsenic, but he should imagine that the pricking process suggested would, if sufficiently severe to reach the hollows in the corn, result in serious skinning of the malt, which would lessen its value, both in appearance and in its powers of resistance to moisture.  He had not been so fortunate as Mr. Overbeck in meeting with gas coke, or in fact any coke, either absolutely or approximately free from arsenic, whilst even the best anthracite was only “practically free” in proportion to the care exercised at the colliery in picking out the lumps of pyrites, some of which might at any moment be overlooked.  He had not yet met with any fuel that could be absolutely relied on, and in all cases had found it necessary to test each truckload, and might add that he found the small powder at the bottom of the trucks to give the most satisfactory indications.

Mr. A. J. Murphy said that he agreed with Mr. Overbeck that bleaching powder was fairly effective in removing scale from the Yorkshire squares, if the scale were newly formed. Quite recently he had come across a case in which it had practically failed to be of real service on scale, which had resulted from many years of neglect; but this was an exceptional case.  He would also like to know whether Mr. Overbeck had tried sodium hypochlorite.  Mr. Murphy agreed with the author that it was difficult to find perfectly faultless stone slabs of suitable size for the construction of squares, and it behooved brewers to look carefully for and watch the consequences resulting from these faults.  In the matter of wired glass, he (Mr. Murphy) had recently seen these in operation in Belgium, but was unable to admit that wired glass was in any sense preferable to unwired glass.  The thickness of the glass seemed sufficient for any practical purpose, and he thought that the presence of the wire in the interior might be rather a source of weakness than of strength.  He also agreed with Mr. Overbeck that much of the arsenic which sometimes occurred in malt was found in the ventral furrow, and brushing failed to remove it, although it might entirely remove any arsenic which was adherent to the outer and rounded portions of the grain.  Indeed, it was easy to prove this point by the very simple experiment of shaking a sample of arsenical malt thoroughly well for a few minutes, when it would be found that it would yield a smaller proportion of arsenic.  Mr. Murphy could not confirm Mr. Overbeck’s opinion that foreign malt meant death to Saccharomyces Pastorianus.  He could, however, say that Saccharomyces Pastorianus meant death to nearly all forms of bacteria, and, under certain conditions, to primary yeasts.  He thought his experience justified him, also, in saying that, however true these statements might be in the case of Saccharomyces Pastorianus they were even more true with regard to Saccharomyces Anomalus, which appeared to have a special property of choking out almost all other species of ordinary yeasts and bacteria, and he would like to know if Mr. Overbeck could corroborate these opinions.

Mr. Overbeck’s statement that bacteria had been less prevalent during the last 2 years, on account of the wet seasons which kept the growths moist and prevented the spores from being blown about, was probably true, and if so it seemed likely that the actual number of bacteria developed would be much greater than usual, and if the coming season happened to be dry and windy, we should be on the lookout for a much greater prevalence of such forms.  Mr. Overbeck had done useful service by drawing attention to the fact that salicylic acid was a natural constituent of many fruits, and it might be added that boric acid had also been shown to exist naturally in many other fruits, such as apples and pears, and therefore although legislation might condemn the use of these antiseptic substances, yet their action had very little of justice about it if it could be proved that Providence provided them gratuitously.  One further point might be touched upon; Mr. Overbeck was one of those close observers whose eyes were always open to every small detail, and Mr. Murphy would like to know whether Mr. Overbeck had traced the effects of sudden changes in the barometer upon the progress of fermentation.  It was noticed, especially in the case of Yorkshire squares, that a drop of four-tenths or five-tenths produced an unmistakable disturbance which required the closest possible attention to the attemporators, if normal results wore to be maintained.

Mr. W. H. Linley said he would like to ask Mr, Ovorbcck to which he gave preference—attemperators or shells.

Mr. E. H. Tetley said if a yeast were used which had been grown in a heavily hopped wort, the pumping would have to be stopped at a lower gravity than when the yeast from a lightly hopped wort, either bitter or mild, had been used.  He would like to ask what was Mr. Overbeck’s objection to filtering yeast with water in place of wort.

Mr. Overbeck, in replying, said there was no rule as to the size of the manhole in comparison to the size of the square.  He had experienced cases where the manhole was too small for the man, but if really done away with, we should have no vessel from which to drain the yeast, and rouse it up with the beer before running the well mixed mass through the valve below.  

As to the best method of cleaning malt, and to what limit the arsenic could be brushed out, it would depend upon how far the arsenic was superficial, or driven in the two porous ends, and the furrow of the grain, but it was possible to base a limit of 1/200 of a grain per 1b.  

With regard to the proportion of pitching yeast, and its best age, no definite answer could be given.  He might, however, state that 77 barrels of wort had been pitched with 7 lbs. of pitching yeast, and yielded 230 lbs. pressed yeast, in contradistinction to Yarmouth brewers, who used 3—4 lbs. per barrel, owing to the heavy percentage of salt in their water.  The system was not the stone square system, yet the beers in that district, in consequence, were very full bodied.  

Blisters were due to fine layers of irregular hardness deposited during false bedding, which the speaker illustrated geologically upon the blackboard.  The cement he had always found satisfactory was the ordinary Portland cement.

His objection to cast-iron squares had nothing to do with the solution of the iron, which did not affect iron back-drink tubs, but was merely one of change of temperature, owing to rapid conductivity.  

He also explained that a process which, in a brisk current of air, could rapidly prick the ends of the malt, and rub them directly amongst themselves, would be most effective against arsenic, and, as he had proved in a new malt-cleaning machine, would not skim the malt.

With regard to the danger of using gas coke in malting, it might vary from practically perfect purity to heavy contamination; unreliability is its greatest danger.  

His objection to filtering yeast with water, and not wort, was owing to the loss of yeast contents when washed by water; if washed with wort, it was fed, washed, and aerated. Fermenting wort, having lost its feeding properties, would on that account also be less suitable. The yeast splash-boards, being made of copper, are best protected by a thick coating of varnish, which only required washing, wore well and were easily renewed.

In reply to Mr. Edmund Tetley’s question, the speaker said the weaker the yeast (as it always was the higher the percentage of hops) the less stable the resulting beer.  Mr. Overbeck said he had treated scales with bleaching powder, which upwards of 10 years and more old the time of action requiring about a fortnight, and the volume of liquid considerable, compared with the amount of scale, since the vessels were filled with a solution of calcium hypochlorite, this being only in a small quantity in the dry substance.  He had not tried sodium hypochlorite, no doubt it would prove more effective but be more expensive.

In reply to the question of size of stones for squares, he laid stress upon the fact of the rarity of really large ones, such as 30-barrel squares.  

He agreed thoroughly with Mr. Murphy as to the dangers of oxidation of wired glass, and also agreed as to the presence of arsenic in malt being concentrated in the furrow, and endorsed strongly the shaking-up idea.  The use of foreign malt in curing Pastorianus difficulties, referring to long foreign, such as Ouchac, etc., appeared to be a new idea, and it was admittedly unknown, but, nevertheless, decided in effect.  

Mr. Murphy had, also, confirmed him that Pastorianus monopolised the whole of the brew at times, by starving out all other germs.  Referring to germs and seasons, he was reminded of the fact that it had been stated that the past year was singularly free from all pathogenic germ disorders.  

Boric acid had been rightly included among natural antiseptics.  Mr. Overbeck could not endorse great differences observable in fermentation during drops in the barometer.

Mr. Murphy moved that the best thanks of the Meeting be given to Mr. Overbeck for his very practical and interesting paper.

The vote of thanks was seconded by Mr. Chubb, and unanimously carried, and suitably acknowledged by Mr. Overbeck.

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