Chapter VII: New Process for the Manufacture of Beer (1)

The principles established in the course of this work implicitly involve the conditions of a new process of manufacture, the essential feature of which would consist in the production of a beer of excellent keeping qualities, we might even say a beer that could not undergo alteration. It will not be difficult now to make ourselves clear on the point.

We have shown in the first place, that the changes which take place in the ferment, the wort, and the beer itself, are due to the presence of microscopic organisms of an entirely different character to that of the ferment-cells properly so called, which organisms, by simultaneously giving rise, in the course of their multiplication in the wort, ferment, or beer, to other products, make the materials difficult to keep or effect their deterioration. Again, we have seen that these change-producing organisms, the ferments of disease, never arise spontaneously in the wort or beer, but, whenever they make their appearance in these fluids, have been imported from without, either in company with the yeast, or from accession of atmospheric dust, or from contact with the vessels, or from the materials themselves which the brewer uses in his manufacture. Moreover, we know that these disease-ferments, or their germs, are destroyed when the wort has its temperature raised to the boiling-point. And, following up the inferences from such facts, we have seen that wort exposed to pure air, after having been heated to boiling, remains absolutely free of any sort of fermentation.

Inasmuch then as the disease-germs of wort and beer are destroyed in the copper in which the wort is boiled, and as, by employing a perfectly pure ferment, we guard against the admission of any foreign ferment of an evil character, we have it in our power to prepare a beer which shall be incapable of undergoing any pernicious fermentation whatsoever. This we shall have effected provided we can take the wort as run off from the coppers, cool and manipulate it out of contact with ordinary air or in contact with pure air, charge it with a pure yeast, and, lastly, store the beer when the fermentation is complete in vessels thoroughly purified from disease-ferments.[162]

§ I.—Preliminary Experiments.

We may readily satisfy ourselves as to the truth of these inferences. The following is one of the earliest experiments which I devised with a view to establish their certainty. Into a flask with a straight neck of about a litre (1-3/4 pints) capacity, a quantity of wort from a brewery was introduced and there raised to boiling, and whilst the vapour still issued from the neck of the flask, connection was made with a two-necked flask in which the cultivation of pure yeast had been carried on. The cork and glass tube used for this purpose had previously been treated with boiling water.

When the wort had cooled down in the flask and matters were arranged as represented in Fig. 75, I raised the two-necked flask so as to cause a little of the liquid and yeast to flow into the wort. Thereupon fermentation was set up, and the resulting carbonic acid gas made its escape by the drawn-out end of the doubled-necked flask. The entire arrangement with its supporting stand remained in this connection for eighteen months, sometimes on a stove, sometimes in the laboratory, exposed to all the variations of external temperature. At the end of that time I tasted the beer in the flask; it was perfectly sound, and the ferment, submitted to the microscope, showed not the slightest trace of any foreign ferments: and, doubtless, the experiment might have been protracted over any number of years with the same result.

The only change that occurs in course of time is the appearance in the neck of the flask at the surface of the beer of a deposit of small prominences resembling a crystallization, but which really consists of those forms of ferment to which in Chapter V. I attached the name of _aërobian ferment_. The beer, after being transferred to a bottle that had been washed with hot water, was kept for several months in the heat of summer, without exhibiting the slightest trace of deterioration.

The essential conditions of the preceding experiment can readily be realized on the large scale. For this purpose we may employ the apparatus in the above sketch (Figs. 76 and 77) constructed of tin or tinned copper. As appears from the sketch, this consists of a cylindrical tub resting on a support, and closed at the top by a cover, whose lower edge fits into a gutter containing water. The wort prepared in the copper is led into the cylinder, a process which does not materially lower its temperature. Now we know that wort in breweries which has been cooled in contact with the air, and so got charged with disease-germs, will, nevertheless, recover its faculty of keeping for any length of time in pure air, if we again raise its temperature to 80° C. (176° F.) or even 70° or 75° C. (158°, 167° F.) Having filled the tub with the hot wort and put on the lid, we then connect, by means of a caoutchouc tube _c d_, the metal tube _a c_ (which opens into one of the tubulures projecting above the lid) with the system of tubes _d e_, _f g_, of which _d e_ is fixed to the cylinder; _e f_ is a caoutchouc junction connecting _e_ with the bent glass tube _g_. We then dash over the apparatus, lid, tubulures, and their corks a quantity of boiling water. This collects in the gutter in which the lid rests, and any excess overflows into a second gutter outside the first, where, however, it cannot remain, but passes away by means of a ring of small holes between the base of the outer trough _i i_ and the cylinder. The overflow is collected in a third trough at the bottom, whence it can be removed by a pipe M. T is a bent thermometer to indicate the temperature of the wort; its bulb is protected by an inlet socket _d d_, pierced with holes; _r_ is a stopcock for discharging the water in the gutter, which serves as a hydraulic junction between the cylinder and its lid; R, V, are stopcocks, or openings for the discharge of the liquid in the cylinder and its deposit. The next process is to cool the vessel, which may be done either by leaving it to itself, or by introducing a current of cold water through the tubulure E, soldered on to the lid. This tubulure is of the form of an inverted funnel, and is pierced at the bottom with a close row of holes, through which the cold water issues in a sheet over the surface of the cover. In whichever way the cooling is effected, the external air continues all the time to enter the vessel beneath the lid by way of the long, narrow passage _g f e d c a_, and must necessarily get purified by depositing in its course all fungoid-germs, just as happened in the case of the two-necked flask of air experiments. This, however, may be still further secured by introducing a small plug of cotton wool, or asbestos, into the end of the tube _g_.

The experiments which we have carried out with this apparatus have proved that, by adopting such an arrangement, beer, a liquid peculiarly liable to change, may be kept as long as we wish, for weeks or months, in contact with air, since the tube _g_ is open, without evincing the least symptom of disease. It matters little whether the leaves and strobiles of the hops are introduced with the hot wort or strained off; the result is the same. On the other hand, a leak in the apparatus from which the wort gets mixed with ordinary water from outside during cooling, will speedily effect a change in the wort and cause it to swarm with vibrios, or butyric ferment, lactic ferment, and other germs of disease, whilst its taste will be rendered extremely nauseous. It can only be through one’s own fault, that is, from want of skill in carrying out the operation, that any change can be brought about by the water in the gutter not being kept out of the fermenting vessel. That water may even become putrid without the organisms contained in it being able to reach the wort in the fermenting vessel. The apparatus may be of any size whatever; we have worked with vessels containing 12 hectolitres with as much ease and certainty as when we used an apparatus of 1 hectolitre (22 gallons).

It is easy to carry out the process of cooling in the presence of carbonic acid gas if we fit a bent tube, similar to _a c d e f g_, to the second tubulure D. Through this tube, or its companion, the gas can be passed as it issues from an apparatus in which it is generated, or from a gasometer filled with it, or from a vessel of beer undergoing fermentation.

However, there is no necessity that the cooling should take place in the fermenting vessel. It may be effected separately, in vessels of greater or less depth, in spiral coils surrounded with cold water, or in any kind of refrigerator, provided always that the conditions of purity are satisfied, and that the flow of the cooled wort takes place under the same conditions. Jets of steam, which are already extensively used for the cleansing of pipes in breweries, may be employed here with great advantage.

The pitching may be effected in various ways. A two-necked flask of a capacity of from 200 to 300 cc. (about 7 to 10 fl. ozs.), in which not more than 100 cc. (3-½ fl. ozs.) of wort has been fermented, will be sufficient for an apparatus of 1 hectolitre (22 gallons), although the flask may not contain more than 1 or 2 decigrammes (1-½ to 3 grains) of yeast. In the manufacture of beer, as at present conducted, the employment of so minute a quantity of yeast would lead to most disastrous results. The fermentation would unfailingly become lactic and butyric, since the foreign germs with which commercial worts and yeasts are always contaminated would have ample time to develop during the first twenty-four or forty-eight hours, whilst the small quantity of yeast used in the pitching could scarcely do more than begin to develop during that time. It is simply with the object of avoiding these secondary fermentations that the brewer uses large quantities of yeast for pitching.

After the wort and yeast have been _pulled up_,[163] a process which every practical brewer adopts after pitching, every part of the liquid is occupied by a multitude of yeast-cells, which seize upon the oxygen in solution, germinate with activity, turn to their own account the food-supplies most easily assimilated, and prevent the growth of the germs of disease-ferments. In the new process which we are now explaining, things happen quite differently. Our wort is pure, and our yeast is pure, and if only a single cell of yeast were introduced into the wort, the vital activity of this would be sufficient to bring about alcoholic fermentation, and to transform the wort into beer, without our having the least reason to apprehend the simultaneous development of any other organisms whatsoever. In short, the new process enables us to pitch with as small a quantity of yeast as we like. It is, nevertheless, inexpedient to employ too minute a quantity, since by doing so we should retard the commencement of fermentation.

In the case of an apparatus of 5 hectolitres (110 gallons) or double that capacity, the pitching may be accomplished by means of flasks holding from 4 to 9 litres (from 7 to 10 or 11 pints), (Fig. 79), or copper cans, tinned inside, holding from 10 to 15 litres (2-1/4 to 3-1/4 gallons), and provided at the upper conical end with glass tubes (Fig. 78). The vessel must be half or two-thirds filled with wort. For this purpose it will be well always to employ wort that has been preserved in bottles by Appert’s process. We must use a stopper provided with tubes, as represented in Fig. 79: _a b_ is a glass stopper which closes the india-rubber tube _b c_; _m n p_ is a fine glass tube, or, better still, made of copper.

The tap R being closed, a long india-rubber tube is attached to the extremity of the curved tube, and the flask is completely immersed in a hot-water bath; the india-rubber tube projects from the bath and keeps the interior of the vessel in communication with the external atmosphere. If the tube _m n p_ is of copper, we may avail ourselves of its flexibility and bend it upwards, so as to place its open extremity outside the bath. The water in the bath is then gradually raised to a temperature of 100° C. (212° F.), at which it is kept for a quarter or half an hour. In the case of copper cans, it is more convenient to place them over a gas-heater. They may be treated in the same manner as the flasks with curved necks. Vessels prepared in this manner may remain in a laboratory, or in any part of a brewery, for an indefinite time, without the wort in them undergoing the least change. It gradually darkens in colour through a direct oxidation of a purely chemical nature, but no tendency to disease will manifest itself.

Some days before we require to pitch an apparatus of several hectolitres, we impregnate one of these flasks or cans.[164] For this purpose we pass the flame of a spirit lamp over the tubes _c b a_ and _m n p_, to destroy the particles of dust that might pass inside at the moment when the stopper _a b_ is taken out, and then by means of a long, straight glass tube we take some of the liquid from a flask or vessel containing pure beer in a state of fermentation, and let a few drops of this, with the yeast that it holds in suspension, fall into the flask or can; the stopper _a b_ is once more passed through the flame and then replaced; generally in the course of one or two days the yeast develops in the flask sufficiently for the fermentation to show itself. We may shorten the operation still further by emptying into the can the contents of one of those double-necked flasks. To do this, we have simply to attach the straight tube of the flask to the india-rubber _b c_, and pour the liquid in. In a similar manner we introduce, through one of the tubulures surmounting the lid of the fermenting apparatus, the contents of the flasks or cans, either whilst they are still in active fermentation, or after fermentation is over. For this purpose, the tap R is connected by means of an india-rubber tube (Fig. 79), with a tube passing through a cork fixed in one of the tubulures of the large apparatus. All this may be done in considerably less time than we have taken to describe it; and the operation may be performed accurately and safely by any one who has witnessed it a few times, even though he may not be skilled in chemical manipulations, especially if he takes care to bear in mind the very simple principles which we have explained.

Since certain parts of the apparatus—the outer opening of the tap, or the india-rubber tubing, for example—may contract particles of dust from the air, those parts, before being used, must be boiled in water, or washed with boiling water, or passed through the flame of a spirit lamp, to destroy the germs mixed with the particles of dust that settle upon them.

The method of cooling the wort in contact with carbonic acid prevents access of oxygen to the latter up to the time of pitching, so that the development of the yeast takes place apart from the influence of oxygen. Now, we know that these conditions necessitate the employment of a very young yeast—a yeast that is in course of active germination, such as may be taken from an incipient preparatory fermentation. Nevertheless, even with this, the development of the yeast under such conditions is extremely slow, and the fermentation takes from fifteen to twenty-five days; whilst, under the same circumstances, but with an aerated wort, it would be finished in from eight to twelve days. This is a considerable drawback, but, perhaps, a still more serious inconvenience is that the beer takes much longer to clarify, and does so with greater difficulty than those beers which are made with aerated worts. At the same time, this is largely compensated by the superior quality of the beer, which is stronger and has greater fulness on the palate, whilst the aroma of the hops is preserved to an extent never found in beers brewed by the ordinary process. Besides this, the yeast deposited at the bottom of the fermenting vessel is much less active, and, being of an older type, is revived with greater difficulty than that which forms in aerated worts. This, which might be considered a disadvantage, if we had to employ the yeast afterwards for pitching, has the great advantage of giving a beer which, when racked, undergoes its secondary fermentation only slowly, and with difficulty.[165] A beer of this kind is better adapted than ordinary beer to stand a long journey without developing great pressure inside the casks, and, if bottled, it will contain very little deposit, and will not froth violently when uncorked. The reason is, that a yeast is the more active, the more ready to multiply rapidly, and to work vigorously the more highly aerated the wort was in which it was grown. On the other hand, a yeast formed apart from air readily gets exhausted, and may even perish in the liquid in which it ferments, when that is kept out of contact with air; in other words, the vital action of yeast is more restricted when it has not been subjected to the action of oxygen during its formation.

If a great depth of wort, the surface of which alone is in contact with atmospheric air, is left to cool down, it will act in almost exactly the same manner as that which is cooled under an atmosphere of carbonic acid gas, because the oxygen of the air is very slow in pervading wort that is undisturbed. The gas will be taken into solution by the upper layer only, whilst the bulk of the liquid will remain unaffected by it. In some experiments which we conducted in a vessel which contained wort to a depth of 70 centimetres (27·5 inches), and which was provided with a tap that enabled us to draw off some of the liquid every day, until we had reduced the depth to 35 centimetres, we found, at the end of eight days, that there was not a trace of oxygen in solution at the latter depth. It is even probable that, considering the slow diffusion of the oxygen, on the one hand, and the combination that may take place between it and certain components of the malt, on the other hand, it would take a long time for all the wort, if undisturbed and of a certain depth, to become saturated with oxygen. In the vessel represented in Figs. 76 and 77 there is a considerable depth of wort to cool down. Nevertheless, the mere fact of the possibility of an aeration from the surface, whilst the wort is cooling down in contact with pure air, is enough to account for a certain effect that is produced on the yeast, later on, for the more youthful appearance of the yeast of the deposit, compared with that which we find in the case of wort cooled in the presence of carbonic acid gas. The difference between the results is particularly striking if, in both cases, we follow up microscopically the development of the yeast during the first few days succeeding the pitching.

The influence of the air on fermentation is considerable. In the ordinary process of brewing, fermentations would be almost impossible, and in every case most defective, if the wort, before being run into the fermenting vessels, were not aerated by its passage over the “coolers,” where the aeration is more or less effective, according as the liquid is more or less shallow. Worts and yeasts being impure, that is containing the germs of foreign ferments, those germs would have time to germinate in the fermenting vessels during the delay that the want of aeration in the wort would cause in the development of the yeast. We are aware that several inventions have been proposed to do away with the coolers, and we feel convinced that the object has been to remedy irregularities in fermentation. Considering the facts which we have published[166] on the development of yeast in the presence of air, and its inactivity in non-aerated media, such inventions ought to be supplemented by some means of further aeration for the prevention of the mischief that they must otherwise cause. In the existing process of brewing, the employment of coolers is a necessity.

The influence of the air on the vital action of the yeast may be proved in ways innumerable. The following is an experiment which we have often carried out with surprising results. A fermentation is going on; we draw off the liquid as rapidly as we please, and pour it back again into the vessel immediately. Within an hour we find a marked increase in the fermentation, evidenced by the liberation of a greater quantity of carbonic acid gas. This experiment may be performed with especial ease if we use the fermenting apparatus that we have described, for, by fitting a gas measurer to the escape tube _a b c d e f g_, the number of litres produced before the drawing off of the liquid may be compared with those obtained after. The least physical change in the running of the fermenting liquid whilst it is being drawn off, modifies the effect in question; such as change in the diameter of the stream, the height from which it falls, its greater or less scattering in falling, all influence it. Again, as might be expected from such results, corresponding modifications take place in the cells of yeast which come under the influence of the air. They become firmer in aspect and outline, their plasma becomes fuller, assumes a younger and more transparent aspect, and the vacuoles disappear. The molecular granulations, too, are less apparent. At a certain focus they disappear; at another they reappear, not as black spots, however, but as brilliant points so small as to be scarcely perceptible. If germination has been suspended it is resumed; in short, everything tends to prove—and having the yeast actually under our eyes we cannot doubt the fact—that the life of the cells is more decided, and the work of nutrition more active after they have been brought into contact with the oxygen of the air, and have absorbed a greater or less quantity of that gas.

Under the ordinary conditions of brewing, the atmospheric air is present in very varying quantities, whether introduced by the wort which holds more or less in solution, or by diffusion over the surface of the vessels, so that the same cells of yeast live by turns without air and with air. At first they absorb all the oxygen held in solution, and multiply under the influence of this absorption. Afterwards, when the supply has been exhausted, and various assimilations have resulted from it, they are deprived of it. Their life continues apart from oxygen, and if the vessel were closed, fermentation would be accomplished under these conditions, although more slowly. The vessel being open, a small quantity of air diffuses continuously through the layer of carbonic acid gas on the surface, and supports the vitality of the cells.

It is interesting to observe that, in the working of breweries, there are several empirical practices the explanation of which is to be found wholly in the fact that the aeration of wort or beer exercises a great influence on fermentation. In many breweries we have seen the pitching performed in the following manner: the brewer, having mixed his yeast in many times its volume of wort, pours all the thick liquid from a height from one bucket into another, and from that back again into the first, and so on a great many times, until the two buckets are filled with the froth enclosing air. In certain London breweries we have seen a bucket suspended by a pulley over the fermenting tun, which is 3 or 4 metres (10 or 12 feet) in depth; this the brewer, by means of a cord, can lower into the tun and pull up again at will, giving it a kind of see-saw movement which agitates the surface of the liquid and aerates it. The use of the fermenting tun itself and the racking of the wort from that tun into casks have the effect of aerating the beer and the yeast, and imparting to the latter a greater vigour and activity.

The resumption of fermentation in cask, after the beer has been run out of the tuns in “low” fermentation breweries is, in our opinion, principally due to the aeration of the beer at the moment when it is racked. The brewer ought to bear in mind that, during racking, every detail is of importance; it makes a great difference whether when the beer is run into the casks it falls from a height or is conducted by a tube to the bottom of the casks, whether it passes directly into the casks, or is poured into them from buckets, and whether it runs in a stream of small or large diameter, since these different methods cause the introduction of corresponding different quantities of air into the beer.

We have devised a simple arrangement for bringing the fermenting liquid into contact with various proportions of atmospheric air. Appended is a sketch of this apparatus (Fig. 80). Instead of one tube serving alike for the entrance and escape of gas, there are two similar ones, each of which opens into one of the tubulures on the cover. Round the other end of one of the tubes is fitted a kind of muff or bag, composed of a cylindrical cage of metallic gauze, over which a layer of well-combed cotton wool is placed, the whole being covered with a muslin bag. The object of this arrangement is to act as an air-filter for retaining the particles of dust. When fermentation has commenced in the apparatus, we have simply to press momentarily the india-rubber connection between the tube from the lid and the tube with the bag. This will at once cause a regular stream of carbonic acid to issue from the end of the uncovered tube, whilst the air will enter by the filtering tube to take its place; and this arrangement will be maintained throughout the whole course of the fermentation, even if we omit the precaution of increasing the power of the syphon by making the tube for the escape of this gas longer than the other one.[167]

It will be readily understood how, whether by this last method, or by the diameter of the tubes, we may vary the conditions of this circulation of air in the apparatus, on the surface of the beer.

§ II.—Method of Estimating the Oxygen held in Solution in Wort.

The use of carbonic acid gas and the cooling of the wort, in contact with that gas or in contact with very limited quantities of pure air, are by no means necessary to the application of the new process. There is only one thing that is absolutely essential—which is, the _purity_ of the gases in the presence of which the wort is cooled and treated. If, therefore, it is well to aerate our wort, either before or during fermentation, this may be done, on the sole condition that the air employed does not introduce any germs of disease that are likely to develop in the beer during fermentation or afterwards. The question of aerating the wort is not, however, so simple a matter as it seems at first sight. A very simple observation will show that wort cannot be safely oxygenated by exposure, without precaution, to the air, even leaving out of account the germs of disease which that air may contain. It is easy to show that finished wort has a decided flavour and aroma of hops, as well as a sweet taste, and that it leaves a certain pleasant, bitter after-taste on the palate. When we taste it in this condition we cannot help thinking that a liquor of the kind, after fermentation, ought to constitute a very valuable beverage, as wholesome as it is pleasant. Now all this pleasant and refreshing sensation that the wort leaves on the palate, which is due as much to the aroma as to the bitterness of the hop, disappears absolutely, we may say, if the wort is left exposed to contact with air for a sufficient time, and that whether the air be warm or cold. We may easily perform the experiment in one of our two-necked flasks, in which we can preserve the wort, in contact with pure air, without any fear of change. The oxygen of the air enters into combination with the substances that the hop introduces into the wort, and the wort, in consequence of this oxidation, gradually becomes transformed into a saccharine decoction, without odour, in which even the bitter flavour is destroyed or hidden. In other words, the wort grows weak and flat, in just the same way that beer and wine do, as well as all the various natural or artificial worts which serve to produce them. Thus it is evident that considerable care is necessary in subjecting wort and beer, whether in course of manufacture or finished, to the action of atmospheric air. If, therefore, it is a good thing to supply wort with oxygen, as we have already pointed out, in order to facilitate the fermentation and nourish the yeast, it is, on the other hand, important that the quantity supplied to it should not be too great, otherwise we may injure the quality of the beer, and particularly its fulness on the palate, that is its apparent strength, which has very little to do with the proportion of alcohol in it. The strength of a beer is intimately connected with those substances introduced by the hops into the wort and thus into the beer, to which we previously alluded, and of which too little is known; their properties and the palatableness resulting from them are very readily affected by the oxygen of the air.[168]

We have, therefore, to ascertain the measure in which air occurs during the process of brewing, and whether, in the actual process, there may not be too great a proportion of active oxygen present. The study of this subject requires that we should know what quantities of oxygen may be held in solution in the wort or absorbed by direct combination. Fortunately this has been rendered a comparatively easy matter by a rapid method of estimating the oxygen held in solution in liquids of various kinds, devised by M. Schützenberger in 1872. As soon as this method was made known, we requested M. Raulin, who was attached to our laboratory as assistant-director, to apply it to the determination of oxygen in wort. This he did with his accustomed skill, devising certain alterations of details which rendered the method at the same time surer and more expeditious.

The principal feature in M. Schützenberger’s process consists in the employment of a salt, the properties of which that chemist was the first to recognize; he has named it _hydrosulphite of soda_, and it is obtained by the action of zinc filings on a solution of bisulphite of soda, out of contact with air.

Hydrosulphite of soda S^2O^2,NaO,HO, which is isomeric with hyposulphite of soda, only differs from the bisulphite by two equivalents of oxygen.[169] When brought into contact with free oxygen, it absorbs that gas instantaneously and becomes converted into bisulphite; similarly when mixed with water, it immediately absorbs the oxygen held in solution. Again there are colouring matters, such as M. Coupier’s soluble aniline blue, that are instantaneously decolourized by hydrosulphite of soda, whilst they resist the action of the bisulphite. If, taking care to avoid the access of air, we add hydrosulphite of soda to a certain volume of water—a litre, for example—that has been deprived of air and faintly coloured with Coupier’s blue, we shall see that a few drops will be sufficient to effect the decoloration. If, on the contrary, the water is aerated, the decoloration will not be effected before a sufficient quantity of the hydrosulphite has been added to absorb the oxygen in solution, and the volume of the reagent required is in proportion to the quantity of oxygen in solution in the water. To render the process sensitive, we must dilute the hydrosulphite to such an extent that 10 c.c., for example, may correspond very nearly with 1 c.c. of oxygen. If the reagent would keep we should only have to determine directly, once for all, the volume of oxygen that a known volume of the liquid could absorb; but, in consequence of its extreme liability to change through contact with air, it is necessary to titrate the liquid every time before using it. This is easily done in the following manner:—

According to the observations of Messrs. Schützenberger and Lalande, the hydrosulphite decolourizes an ammoniacal solution of sulphate of copper, reducing the copper to a lower state of oxidation; the sulphite and bisulphite having no action as long as there is an excess of ammonia. We prepare a strongly ammoniacal solution of sulphate of copper, containing such a quantity of copper that 10 c.c. of the liquid will correspond, as far as action on the hydrosulphite is concerned, with 1 c.c. of oxygen. Calculation by equivalents gives us the correct value verified by direct experiment.[170]

The object of the modification which M. Raulin has introduced, is to avoid the loss of time thus occasioned by the changes which take place in the titrated liquids by long keeping, as well as certain errors which may arise from the acidity of the wort. On this latter point M. Schützenberger has remarked that the quantities of hydrosulphite of soda corresponding with one and the same volume of oxygen vary with the acidity of the liquid operated upon, a phenomenon which that skilful chemist explains by the formation of oxygenated water, of varying stability in media of different acidity.

Instead of determining the strength of the titrated solution of hydrosulphite before each operation, we take the solution as it happens to be, and determine its strength by causing it to act on a known volume of pure water saturated with oxygen at a certain temperature. The tables of solubility of oxygen in water give the exact volume of oxygen on which the measured volume of hydrosulphite used has acted. According to Bunsen, about one minute’s brisk shaking in a closed bottle, with excess of air, will be sufficient to effect the maximum saturation of the water at the temperature at which we operate.

For experiments on wort we require:—

1. A 2-litre (3-½ pints) flask, A, containing _saturated_ hydrosulphite of soda,[171] of such strength that 2·5 c.c. will be sufficient to absorb almost all the oxygen in 50 c.c. of water saturated with air at the ordinary temperature (that is, 1 volume of hyposulphite must equal 20 volumes of water).

2. A 2-litre flask, B, containing a solution of indigo-carmine, 50 c.c. of which will be decolourized by about 20 c.c. of the hydrosulphite. This solution contains about 20 grammes (30·7 grains) of commercial indigo-carmine per litre (1·76 pints).

3. An apparatus, C, for the production of hydrogen.

4. An experimental apparatus composed of a burette, D, graduated in tenths of a cubic centimetre, and a three-necked Wollf’s bottle, E.

5. A flask, F, holding about 100 c.c. provided with a straight tube divided into tenths of a cubic centimetre, and containing a solution of ammonia of such strength that about ten drops of it will neutralize the acidity in 50 c.c. (1·76 fl. oz.) of wort.

To perform the operation we shake about 150 c.c. (5·3 fl. oz.) of distilled water, at the existing temperature, in a 1-litre flask for a minute or so; this saturates it with air, and we must at the same time note the temperature. To be extremely precise, we should note also the barometrical pressure.

Into the bottle E we introduce about 50 c.c. of the indigo solution, and 200 c.c. of water at about 60° C. (140° F.), and fill the tube _e_ to the point _b_ with water saturated with air; we then expel the air from the bottle E by a current of hydrogen. The blue colour of the liquid in the bottle is then very carefully brought to a yellow tint, by running in, drop by drop, the hydrosulphite with which the burette D is filled.

We next pour 50 c.c. of distilled water saturated with air into the funnel _a_, and pass it into the flask; the blue colour reappears. We must then bring back the colour to exactly the same tint of yellow. Let _n_ represent the number of divisions on the burette denoting the volume of hydrosulphite employed for this purpose.

We repeat this last operation immediately, taking 50 c.c. of the wort, the oxygen of which we wish to determine, having first introduced into the funnel _a_ a sufficient number of drops of the ammoniacal solution to neutralize the acidity of the wort. Let _n´_ represent the number of divisions of hydrosulphite employed to restore the yellow tint in the case of the wort.

We once more perform the experiment with 50 c.c. of saturated water; let _n´´_ be the number found.[172]

The ratio which the quantity of oxygen held in solution in the wort bears to the quantity of oxygen contained in the same volume of water saturated with air, at the temperature _t_, and under the pressure H, will be

it will be sufficient in most cases to bear in mind this ratio.

When we want to deduce the absolute quantity of oxygen held in solution in a volume V of the wort, we have merely to multiply this ratio by the quantity of oxygen contained in the same volume of water saturated with air, at the temperature _t_ and under the pressure H, a very simple problem if we know the coefficients of the solubility of oxygen in water at different temperatures. These coefficients are given for ordinary temperatures in the following table, which was compiled by Bunsen. We have restricted the numbers to three places of decimals:—

Temperatures. Coefficients.
0° C. (32° F.) 0·040
1° C. (33·8° F.) 0·040
2° C. (35·6° F.) 0·039
3° C. (37·4° F.) 0·038
4° C. (39·2° F.) 0·037
5° C. (41·0° F.) 0 036
6° C. (42·8° F.) 0·035
7° C. (44·6° F.) 0·035
8° C. (46·4° F.) 0·034
9° C. (48·2° F.) 0·033
10° C. (50·0° F.) 0·033
11° C. (51·8° F.) 0·032
12° C. (53·6° F.) 0 031
13° C. (55 4° F.) 0·031
14° C. (57·2° F.) 0·030
15° C. (59·0° F.) 0·030
16° C. (60·8° F.) 0·029
17° C. (62·4° F.) 0·029
18° C. (64·4° F.) 0·029
19° C. (66·2° F.) 0·028
20° C. (68·0° F.) 0·028

The primary condition which enables us to rely on the exactness of this method is the fact which we have mentioned above, that a liquid if shaken up with air for one minute will become perfectly saturated with oxygen. Substantially this is the case. In estimating the oxygen in different parts of a liquid treated thus, we have invariably obtained the same figures to within about 1/50th.

It is true that the variable quantity of the oxygen held in solution in the liquid contained in the part of the tube _eb_, as well as the oxygen absorbed during the treatment of the liquid in contact with air, constitute causes of error. Experience, however, proves that these causes of error are insignificant, as long as we have to deal with a liquid the aeration of which is not very far removed from the point of saturation, and whose solubility-coefficient for oxygen is not widely different from that of water for the same gas. Under such conditions we have always found a constant ratio, to within about 1/40th between the same liquid and air-saturated distilled water, placed under the same circumstances.

If, on the other hand, we have to deal with a liquid which holds but a minute quantity of oxygen in solution, the causes of error mentioned may very seriously affect our results, and it will be absolutely necessary to avoid them. The liquid experimented on must be treated out of contact with air, by aspirating it directly from the vessel that contains it into the pipette H, which is graduated for 50 c.c., and causing it to pass thence into the flask E, by substituting the pipette for the funnel _a_. Finally, before arranging the pipette, we cause a small quantity of the liquid in the flask, which has been previously brought to the exact yellow tint, to pass, by pressure, through the tube _eb_, so as to avoid the cause of error that is likely to result from the air held in solution in the liquid of that tube.

The liquid, the oxygen of which has to be determined, may also be passed directly from the vessel containing it into the flask E; the rest of the operation being performed as already described.

It was by this method that the oxygen held in saturate solution in wort was determined. The following are the principal results obtained by M. Raulin:—

1. At different pressures the ratio between the quantities of oxygen held in solution in water and in wort is, all other conditions being similar, constant. This ratio has been found equal to 1·20 in the case of wort and water saturated with air at the ordinary pressure, and 1·24 in the case of wort and water saturated with pure oxygen.

2. The ratio between the coefficient of the solubility of oxygen in water and that of its solubility in wort is very nearly constant at different temperatures, increasing, however, slightly as the temperature diminishes.

This ratio has been found to be—

Temperatures.
26° C. (78·8° F.) 1·20
19·5° C. (67·1° F.) 1·25
4° C. (39·2° F.) 1·37

Another wort gave the following results:—

Temperatures.
9° C. (48·2° F.) 1·15
21° C. (69·8° F.) 1·10
25° C. (77·0° F.) 1·07

3. The ratio between the quantities of oxygen held in solution in water and those held in solution in wort increases with the concentration of the wort. By evaporating the same wort to different degrees of concentration, and afterwards saturating it with air, at the same temperature, we obtained the following figures for the ratio in question:—

Weak wort 1·06
The same evaporated to half 1·15
“ ” “ 2/5 1·27
” “ ” 3/10 1·45
“ ” “ 1/6 1·96

4. Worts of different origin, but of the same density and temperature, when saturated with oxygen, always contain very nearly the same quantity of that gas.

Two portions of the same wort, shaken up with air, one being hot the other cold, then left to themselves for some time, and afterwards saturated with air, at the same temperature, gave the figures 1·22 for the ratio between the oxygen in the water and that in the wort.

Different worts of the same density, saturated at a temperature of 15° C. (59° F.), gave the following ratios:—

Wort kept in a bottle with air for 19 1·140
months

Wort recently prepared 1·142

Wort kept in a bottle without air for 20 1·142
months, aerated for 18 days

Wort evaporated to dryness and made up 1·126
with water

5. The solubility of oxygen in wort differs very little from the solubility of oxygen in sweetened water of the same density.

An experiment was made with a solution of sugar on the one hand, and with wort more or less diluted with water on the other hand, at the same temperature of 11° C. (51·8° F.). The following figures were obtained for the ratios of solubility:—

Solution Wort.
of Sugar.

Marking 17·9° 1·278 1·27
Balling[173]

“ 14·0° ” 1·190 1·15

“ 7·0° ” 1·092 1·06

6. From the preceding results it is easy to deduce a general formula which shall give the coefficient of solubility of oxygen in any wort, marking B° by _Balling_, and at temperature _t_°.

From the figures of (2) it follows that above and below the temperature of 15° C. (59° F.), the ratio which the coefficient of solubility of oxygen in water bears to that of the solubility of the same gas in wort varies about 0·006 for each degree of the thermometer. From the figures of (3) it follows that the same ratio varies about 0·002 for each degree of _Balling_ above and below the 15th degree on the instrument.

By taking _c_ for the coefficient of solubility of oxygen in water at _t_° C., and _c´_ for that of oxygen in wort also at _t_° C., and having a density B, by _Balling_ at 15° C.; and taking X for the ratio _c_/_c´_, at 15° C. and 15° _Balling_, we shall have

_c_/_c´_ = X + (B - 15) 0·022 - (_t_ - 15) 0·006.

By carefully ascertaining the ratio _c_/_c´_ for different worts, and adopting the preceding formula, we have found for X a mean value of 1·16.

The definitive formula, therefore, is:

(1) _c_/_c´_ = 1·16 + (B-15) 0·022 - (_t_ - 15) 0·006,

or again,

(2) _c_/_c´_ = 0·86 - (B - 15) 0·016 + (_t_ - 15) 0·004.

The coefficient _c_ of the solubility of oxygen in water will be found in the table given a few pages back.

§ III.—On the Quantity of Oxygen existing in a state of Solution in
Brewers’ Worts.[174]

The wort, when it comes from the copper in which it is boiled with the hops, remains exposed upon the coolers for a time, the length of which varies according to circumstances, the most important of which is the exterior temperature. The average time is from seven to eight hours, during which the volume of the wort diminishes, whilst its density increases; at the same time, it deposits its proteinaceous matters and absorbs oxygen from the air, either by way of solution or of combination.

In the present paragraph we shall confine ourselves to the uncombined oxygen held in a state of solution in wort, recognizable by the change of colour produced by its action on white indigo.

The use of the coolers enables the brewer to obtain his wort in two distinct states of limpidity—filtered wort and unfiltered wort. At the same time there is a further difference between these worts, namely, in the quantity of oxygen held in solution. The unfiltered wort comes direct from the coolers; the wort to be filtered, mixed with a part of the deposit, is run into a special vessel, from which it is distributed over the filtering surfaces, which are generally of felt; filtered bright, it is then received in a reservoir, from which it is distributed amongst special fermenting vessels. Falling through the air in a thin stream of drops, it must necessarily have become charged with a greater quantity of oxygen than ordinary wort. In good breweries it is put apart by itself to ferment, and the yeast which it yields is firmer and deposits more easily than that of unfiltered wort. As for the fermentation, it is, under similar conditions, quicker by a day or a day and a half than in the case of ordinary wort. The difference in the quantity of oxygen held in solution in the two kinds of wort is greater in proportion as the external temperature is lower; in winter it may be twice as great as in summer. The reason is that in summer a boiling wort does not obtain a minimum temperature of 20° C. (68° F.), on the best coolers, in less than six or seven hours. After leaving the coolers it is passed over a refrigerator. In winter it attains that temperature in about three hours, or less, which then goes on sinking on the coolers. During the last two or three hours which are employed in bringing the temperature still lower, as also during the running off, the wort absorbs an appreciable quantity of oxygen. In other words, wort in winter remains for a longer time at low temperatures, in free contact with air.

Another circumstance unites with this exposure upon the coolers to increase the aeration of the wort; the wort is run into the fermenting tuns through pipes of large sectional area, more or less bent, and carries with it by suction considerable quantities of air, which, from the continual agitation, gets well mixed with it. The effect of this mixing in the pipes is to considerably increase the proportion of air in solution in the wort, especially in winter, when the temperature of the wort is lower; and from the figures given below we may, although it is very variable, put the average increase at a quarter of the whole amount. The calculation has been made by comparing the quantities of air held in solution in two samples of the same wort, one of which was taken from the coolers at the moment of “turning out,”[175] and the other from the fermenting vessel after it was filled.

Let us call the ratio between the quantity of oxygen held in solution by a wort, and that which the same wort would hold in solution if saturated at the same temperature, the _degree of saturation_ of that wort at the temperature _t_.

The determination of degrees of saturation is reduced to a comparison of the number of divisions of hydrosulphite _n_ which satisfies the wort in the first case, with the number _n´_ corresponding with the same wort saturated at the same temperature. The ratio _n_/_n´_ gives the degree of saturation at the temperature _t_.

In experiments made with a wort at 14·5° _Balling_ as mean density, we found the following results:—

In summer, in the case of worts reduced to the temperature of 5° C. (41° F.) by a refrigerator, the degrees of saturation may be set down as—

For unfiltered worts 0·500
For filtered worts 0·800

In winter, in the case of some worts which were racked at a temperature of from 3° to 4° C. (37·4° to 39·2° F.), without the use of a refrigerator, we found the saturation complete in both worts. In the case of a very low external temperature, however (-10° C., 14° F.), we have failed to determine the saturation in an unfiltered wort. As regards the mean winter figures, in the case of worts racked at a temperature of 5° C. (41° F.), they may be fixed at these:—

For unfiltered wort 0·850
For filtered wort 0·950

In autumn and spring we find the mean figures to be intermediate between those given above:—

For unfiltered wort 0·500 to 0·850
For filtered wort 0·800 to 0·950

From these ratios it is easy to find the quantity of oxygen contained in brewers’ worts, if we also refer to Bunsen’s Tables and the formula (2) given in the preceding section. At the temperature of 5° C. (41° F.), at which the above worts were “gathered,”[176] and not taking into account the very small correction that should be made for the difference of half a degree on Balling, we find, by this formula, as the ratio of the coefficients of the solubility of oxygen in saturated wort and in water—

_c´_/_c_ = 0·82

Now, at the temperature of 5° C., the quantity of oxygen held in solution in 1 litre of water is, according to Bunsen, 0·036 litre, at the atmospheric pressure, and therefore at the pressure of 1/5th atmosphere, which is that of the oxygen in atmospheric air, it will be—

0·036/5 litre = 7·2 c.c.—[that is, 2 cubic inches per gallon.]

And, consequently, in the case of saturated wort, it will be—

7·2 c.c. × 0·82 = 5·904 c.c.—[that is, 1·62 cub. inches per gall.]

Multiplying this last number of c.c. by the different _degrees of saturation_ found, we shall obtain the volumes of oxygen held in solution in 1 litre of different worts:—

Summer worts {Unfiltered 0·500 × 5·904 c.c. = 2·952 c.c.
{Filtered 0·800 × 5·904 “ = 4·723 ”

Winter worts {Unfiltered 0·850 × 5·904 “ = 5·018 ”
{Filtered 0·950 × 5·904 “ = 5·609 ”