Chapter VII: New Process for the Manufacture of Beer (2)

It is important to notice that we are here dealing with wort taken from the fermenting vessel just before it was pitched; that is to say, when the quantity of oxygen held in solution was as large as the treatment to which it had been subjected allowed of its being. The mode of taking it for examination is as follows:—A burette, H (Fig. 81), is plunged into the fermenting vessel, the temperature of which at the time is ascertained very exactly, the upper part of the burette being fitted with an india-rubber tube, _a b_, longer than itself. The liquid is then sucked up the tube, and soon completely fills the apparatus and runs out at _b_ (Fig. 82). By lowering the tube the whole arrangement thus forms a syphon, and enables us to let the wort that we are experimenting on flow for some minutes; when every trace of air has been thus expelled, the lower tap is closed and the liquid is introduced into Schützenberger’s apparatus.

As for the saturated wort, the value of which in oxygen serves to determine one of the elements of the degree of saturation, it is readily obtained by introducing a volume of from 100 c.c. to 150 c.c. of wort into a 2-litre or 3-litre flask, and shaking it briskly so as to saturate it with air; it is then poured into a settling-glass, to separate it from the great quantity of froth formed in the shaking, and then, by means of a graduated pipette, 50 c.c. is taken for examination.

We have spoken of the influence that oxygen has on the activity of yeast, on its development and, consequently, on the progress of fermentation. Moreover, we know, from experiments already mentioned, which we communicated to the Academy and the Chemical Society in 1861, that the rapid development of yeast in contact with air is in reciprocal relation to the disappearance of the oxygen from the air. Knowing the conditions of the aeration of wort from the moment when it arrives on the coolers until the moment when, in the fermenting tun, it is about to be pitched, it would be interesting to ascertain what happens to the oxygen dissolved in the wort at the moment of pitching, how yeast is affected when suddenly brought into contact with that oxygen; what part, in short, that gas plays in fermentation.

Let us therefore follow up, hour by hour, the degree of saturation after pitching, in Tourtel’s brewery. On November 4th, 1875, some wort at 14° Balling was pumped on to the coolers at 7 p.m., and at 4 a.m. went down to a 32-hectolitre (700 gallons) tun, its temperature then being 6° C. (42·8° F.) The pitching, in which about 100 grammes (3·2 oz. troy) of pressed yeast was used per hectolitre (22 gallons), took place at 5 a.m. The following is the curve of the degrees of saturation of the oxygen, as drawn by Messrs. Calmettes and Grenet.

The abscissæ represent the time expressed in hours, and the ordinates give the degrees of saturation of the wort with oxygen. It will be seen that about twelve hours after the pitching, and at a temperature of 6° C., all the oxygen had disappeared, absorbed by the yeast. We shall find that wort by itself, unassociated with yeast, would also have combined with oxygen; but in the course of twelve hours, at 6° C., this combination would have been scarcely appreciable in absence of yeast. It follows, therefore, that the oxygen in solution is taken up by the yeast, under the conditions of which we are speaking. This has been proved directly by an experiment. A double quantity of yeast was employed for a tun similar to the preceding one, and it was found that the oxygen in solution disappeared completely in less than half the time that it took to disappear in the first case.[177] It is very important to notice that in our 32-hectolitre tun, at the moment when we determined the complete disappearance of the oxygen in solution, the cells of yeast had assumed a younger and fuller appearance than they had at first; but they had not multiplied at all up to that time, nor were there even any buds then visible on them. The oxygen, therefore, must be stored up somehow in the cells, taken up by their oxidizable matters to be brought into work subsequently, or to act as a _primum movens_ of life and nutrition, spreading its influence over several successive generations of cells.

§ IV.—On the Combination of Oxygen with Wort.

The atmospheric oxygen is not merely taken into solution by wort; it also combines with it, as a very simple experiment will suffice to show. If we place in a tinned iron vessel some boiling wort, separated from the hops in the copper, and cool it suddenly by plunging it into iced water, and after having cooled it down in this manner to 15° or 20° C. (59° or 68° F.), saturate it with oxygen, by shaking it briskly in a large flask, and then completely fill a vessel with it and close it up for twelve hours, we shall find at the end of that time, if we test it with the hydrosulphite of soda, as we have described in § II., that it does not contain a trace of free oxygen. The whole of the gas which was originally held in solution will have entered into combination, that is to say, the liquid, first coloured blue with the indigo-carmine, and then brought to a yellow tint by means of the hydrosulphite of soda, will not regain its original blue colour through the action of this wort. The following experiments were undertaken with the object of studying this property of wort, and in order that we might form some idea of its importance, and of the total quantity of oxygen that wort can absorb under certain special circumstances. The experiments were performed in our own laboratory on wort from Tourtel’s brewery, which M. Calmettes had forwarded to us in bottles prepared in the brewery at Tantonville, in the following manner: Each bottle was filled with boiling wort taken from the copper and closed with a bored cork, through which the neck of a funnel passed; the funnel also was filled with the wort, and the whole preserved from contact with air by a layer of oil. The next day the bottles were corked full by the help of a bottling needle,[178] previously heated, with perfect corks that had been passed through the flame. The bottles arrived in Paris in very good condition, quite full of the liquid up to the corks. They were left undisturbed for one or two days at the same temperature as that to which they had been exposed during the corking and the journey. The object of this was to afford time for a deposit of the wort to form at the bottom of each bottle. As a matter of fact, we know that wort boiling in the copper is charged with proteinaceous matters and other floating and insoluble substances. The wort above the deposit was turbid and opaline; it was in this state when we used it for our experiments. It may be taken for granted, without risk of appreciable error, that the wort had been absolutely deprived of oxygen in solution, inasmuch as it had been bottled when boiling, and had cooled down out of contact with air. As for the quantity of oxygen that it might have held in combination, this must have been insignificant, although there must have been some, since the wort had been exposed to the air in the copper; the oxygen in combination, however, could have had no appreciable influence on the results which we obtained. Let us call this wort _boiled wort_.

_First Experiment._—Into a straight-necked flask we introduced a certain measured quantity of this wort by means of a syphon, taking care that the syphon should only act on the opaque wort, and should not reach the deposit at the bottom of the bottle. We then drew out the neck to a fine tube in the flame and boiled the wort; and during ebullition we sealed the end of the fine tube. After it had cooled, we arranged that pure air should enter the flask. To do this we made a file mark near the fine closed point of the flask, and connected the point by a piece of india-rubber tubing with a glass tube containing a column of asbestos, which we heated. We then broke off the point of the flask inside the india-rubber tube, so that the air entered the flask after being filtered through the asbestos. We removed the india-rubber tube and sealed up once more the fine end of the neck at the point where we had broken it off. Finally, to aerate the wort to saturation, we shook the flask briskly for some minutes, and then placed it in a hot-water bath, where we left it for about a quarter of an hour. We afterwards removed it to an oven at 25° (77° F.). We repeated the same operation next day and the four succeeding days.

The wort, which at first was scarcely coloured, gradually assumed a reddish-brown tint, and deposited an amorphous matter, but without brightening. It became clear, however, when filtered, which was not the case with the turbid, opaline wort in the bottles when they arrived.

The following is an analysis of the air in the flask, made immediately after a renewed and vigorous shaking, the object of which was to saturate the wort with air before analyzing the supernatant air:—

November 29th.

Temperature at which the flask was refilled with air 4° C.
(29·2° F.)

Atmospheric pressure 751 mm. (29·6 ins.)

Total volume of flask 333 c.c. (20·32 cub. in.)

Volume occupied by the wort 120 “ ( 7·32 ” )

December 8th.

Volume of gas analyzed 27·6 c.c. (1·68 cub. ins.)

After treatment with potash 27·4 c.c. (1·67 “ )

” “ pyrogallol 22·4 ” (1·36 “ )

Oxygen 5·0 c.c. (0·305 cub. in.)

Composition of the gas:— Per cent.

Oxygen 18·25

Nitrogen 81·57

The formula which we deduced above (§ II.) allows us to conclude that at the temperature of 8° C. (46·4° F.), which was the temperature at which the wort was saturated before the analysis given above, the quantity of oxygen in solution in the 120 c.c. (4·2 fl. oz.) of wort was 0·84 c.c. (0·051 cub. in.).

At the moment when the flask was closed, the total volume of oxygen, calculated to zero and 760 mm. (30 in.) pressure, was 44·73 c.c. (2·729 cub. in.).

At the moment when the analysis was finished, the volume of oxygen was calculated to the same conditions of temperature and pressure, 38·86 c.c. (2·355 cub. in.); 5·87 c.c. (0·374 cub. in.) has, therefore, disappeared. Now, as there is 0·84 c.c. (0·051 cub. in.) in solution, there has, consequently, been an absorption, by combination with 120 c.c. of wort, of 5·03 c.c. (0·32 cub. in.) of oxygen, or 41·7 c.c. per litre (11·6 cub. ins. per gallon).

_Second Experiment._—In a similar experiment, in which, however, the flask was kept for five days at a rigorously constant temperature of 55° C. (131° F.), day and night, and in which the supernatant air was not shaken up with the wort, we found—

Volume of gas analyzed 28·5

After treatment with potash 28·3

“ ” “ pyrogallol 23·0

Oxygen 5·3

Composition of the gas:— Per cent.

Oxygen 18·6

Nitrogen 81·4

Total oxygen at first 29·40

“ ” remaining 26·04

“ ” that has disappeared 3·36

“ ” in solution 0·54

“ ” in combination 2·82

Or per litre, 35·2 c.c. (9·8 cub. ins. per gallon).

The colour of the wort in this experiment had become sensibly similar to that of the wort in the preceding experiment.

_Third Experiment._—In another experiment we left the flask, for the same length of time again, after it had been refilled with air and reclosed, at a temperature which varied between 2° and 4°C. (35·6° and 39·2° F.). In this case we found—

Volume of air analyzed 27·8

After the action of potash 27·8

After pyrogallic acid 22·3

Oxygen 5·5

Composition of the gas:— Per cent.

Oxygen 19·7

Nitrogen 80·3

Total oxygen at first 29·40 c.c.

“ ” remaining 27·58

“ ” that has disappeared 1·82

“ ” in solution 0·44

“ ” in combination 1·38

Or per litre, 17·20 c.c. (4·8 cub. ins. per gallon).

In this last experiment the wort was scarcely darker in colour. Its colour, compared with that of wort cooled on the coolers in the brewery, was slightly darker; but the difference, although it existed, was scarcely appreciable. We shall revert to this fact, which is of importance, presently.

_Fourth Experiment._—The following series of experiments were undertaken to enable us to form some idea of the rapidity with which oxygen is absorbed by wort.

We employed three flasks. A, B, C, of the following capacities:—

A = 234

B = 214

C = 203

into which we introduced the following quantities of wort (boiled wort, without air):—

Into A 96 c.c.

“ B 84 ”

“ C 84 ”

The necks of the flasks were then drawn out and sealed in a flame, the liquid being at a temperature of 5° C. (41° F.). The flasks were then placed in a hot-water bath and kept at 100° C. (212° F.) for a quarter of an hour. The flask A was repeatedly shaken during cooling, as also was the flask B, this being omitted in the case of the flask C.

The contents of flask A were submitted to analysis as soon as it was quite cooled—that is to say, in about three hours. The analysis of contents of B and C was delayed for about twenty-four hours. We took the precaution of not commencing the analysis before we had shaken the flasks for a few minutes, so that the wort in all of them might be saturated at a fixed temperature, and thus enable us to ascertain the exact quantity of oxygen in solution.

The analyses showed that the worts in the three flasks contained:—

Flask A, oxygen in combination, per litre 20 c.c.

“ B, ” “ ” 21·4 c.c.

“ C, ” “ ” 16·8 c.c.

Several facts may be deduced from these experiments: the shaking up of the wort with air has a marked effect on the absorption; a very appreciable absorption immediately follows the shaking up of the wort when warm; whereas, in the case of cold wort that has remained undisturbed, the absorption takes place slowly.

The results of the preceding experiments plainly show that the wort, which is very hot when it comes on to the coolers, where it remains for several hours, must absorb an appreciable quantity of oxygen by combination; but these same experiments teach us nothing definite concerning the volume of oxygen that is actually absorbed. We can only gather from the remark which concludes the third experiment given above, that the total quantity of oxygen absorbed by the wort in Tourtel’s brewery, during the time that it remains on the coolers, must be less than 17 c.c. per litre (4·7 cubic inches per gallon), inasmuch as the coloration effected by combined oxygen in the proportion of 17 c.c. per litre was considerably greater than that of the wort taken from the backs in the brewery.

If we knew the curve of cooling on the Tourtonville coolers we might easily, in experiments conducted in our laboratory, assimilate the conditions of our experiments to those of the oxidation of the wort in the brewery, by exposing wort in contact with air in closed flasks to temperatures varying according to the indications of the curve in question. For this purpose, we induced M. Calmettes to study the process of cooling upon the coolers at Tantonville. In Fig. 84 the figures found in one of that gentleman’s experiments are given.

The abscissæ represent the time expressed in hours; the ordinates, the degrees of temperature. The exterior temperature was 0° C. (32° F.); the atmosphere was calm. The wort was pumped on to the coolers at 5.20 p.m., its temperature then being 85° C. (185° F.), and the operation of pumping lasted from 5.20 to 5.30 p.m. The first determination was made at 5.30 p.m., and was repeated every ten minutes until 7.30 p.m. Between 7.30 and 8.30 p.m. it was repeated every twenty minutes; after that, it was repeated every half-hour until 2 a.m., when the wort went down to the fermenting vessels. The mean depth of the wort was 8·5 centimetres (3·1 inches).

Having determined the rate of cooling in the brewery, we made the following experiment: a known quantity of wort from the copper—deprived, consequently, of oxygen—in the same condition as when it comes on the coolers, was put into a graduated, cylindrical vessel, which was then closed with an india-rubber cork, and placed immediately, without being shaken, in a hot water bath at 85° C. (185° F.). Another vessel similar to the preceding one, and having a thermometer passed through the cork, and immersed in the wort, enabled us to observe the temperature. The temperature was gradually reduced, in exact accordance with the data of the preceding curve, until the water, in the course of eight hours and a half, was brought down to 10° C. (50° F.). It is true, that we cannot pretend to have realized all the conditions of the coolers, in this manner, but we approached them very nearly; moreover, it was an approximation rather than a rigorous determination that we desired to obtain. We then collected over mercury the air which remained in the flask, and analyzed it very carefully; at the same time, with Schützenberger’s apparatus, we determined the oxygen held in solution in the wort so treated. From the results thus obtained we easily found the quantity of oxygen that had disappeared—that is, the oxygen which the wort had acquired from the atmosphere of the flask, and which had combined with the oxidizable matters of the wort.

The volume of the flask being 815 c.c., that of the wort 391 c.c., and the depth of the liquid 8 cm., we found an absorption by combination of 9·49 c.c. of oxygen per litre of wort (2·63 cub. ins. per gallon). Another flask treated in the same manner gave us similar results.

As the oxygen in solution has so great an influence on fermentation, it is important that we should, likewise, know the effect produced by the oxygen in combination. The following considerations and experiments may throw some light on this subject:—

We have already remarked that natural saccharine worts oxidize, and acquire colour in contact with air, and that this coloration disappears when these worts are caused to ferment. This furnishes one presumption, that the oxygen in combination disappears then, from, being abstracted by the ferment. A similar phenomenon is observable in the case of wort. After having acquired a marked dark shade by remaining in contact with pure air, it loses this colour very appreciably during fermentation; and if the wort does not quite regain the colour which it originally had when it came from the copper, this circumstance is probably owing to the fact that the quantity of oxygen in combination with the wort is larger than that which is abstracted by the yeast. We have seen that yeast absorbs oxygen, since, in the case of a saccharine wort, more or less saturated with oxygen in solution, when fermentation commences, the first effect of the ferment is to cause that oxygen to combine with its own substance. We should, therefore, expect to find the oxygen in combination, as well as that held in solution, in wort, abstracted by the yeast and contributing to the activity of fermentation. As a matter of fact, this is proved by direct experiments, for the fermentation of a wort that has oxidized in contact with air, or of one from which all the oxygen that was held in solution in it has disappeared by direct combination, is much more easy, rapid, and complete than the fermentation of the same wort when it contains no oxygen, whether free or combined. These experiments were as follows: we boiled some _copper wort_ in a large double-necked flask, like those shown in Fig. 73; all the air being expelled, pure air was allowed to enter the flask; and when the wort was cool it was saturated with this air, by being shaken briskly for a quarter of an hour. The wort was then forced by a pressure of air, applied to the extremity of the S-shaped tube, into smaller flasks, similar to the preceding ones; these we filled completely, and then plunged the end of their sinuous tubes under mercury. After waiting for two or three days, a longer time than was required for the oxygen in solution to enter into combination—a fact which we confirmed by means of a similar flask, which served as a standard—we caused the wort, so prepared, to ferment in the flasks, and side by side, for the sake of comparison, some _copper wort_ that contained no air in solution or combination.

In other experiments we operated on pure wort, saturated with oxygen in combination, by being allowed to remain for one year in an open flask in contact with pure air. This wort was deprived of air in solution by a protracted boiling over mercury. It was then pitched, out of contact of air, with an old yeast. The yeast underwent no development at all, a proof that oxygen in combination cannot act like oxygen that is free, or simply in solution, in effecting the revival of the yeast; nevertheless, after the revival has been once started by means of a small quantity of air, fermentation declares itself with much greater facility than in the case of copper wort, placed under the same conditions, but deprived of oxygen in combination.

§ V. On the Influence of Oxygen in Combination on the Clarification of
Wort.

Oxygen in combination has another effect which it is essentially important to point out, for it concerns the clarification of beer. One of the most valued properties of this beverage is its limpidity and brilliancy. We know from the results of the fourth experiment in the preceding paragraph that in the case of a wort shaken up when hot with air, and examined as soon as cold, that is, after an interval of only three hours, we find a notable volume of oxygen to have been absorbed by combination; in the experiment to which we allude, this volume was not less than 20 c.c. of oxygen per litre of wort. The shaking up of the wort when cold with air saturated it with oxygen in solution, but the quantity of oxygen which under these conditions entered into combination, in the course of three hours, is insignificant, although saturation by solution may be attained in the course of one minute’s shaking. If two samples of the same wort are shaken up with air, one of them being hot and the other cold, and both filtered after having been left undisturbed for twenty-four hours, or even immediately after the agitation, we cannot fail to be struck with the great difference that they will present in point of brightness. The wort that was shaken up hot will have more colour, and will be brilliant; the other will be turbid, and will not become clear for five or six days, when left to itself in contact with air and filtered again. This explains a fact that may be easily verified in practice: Boiled wort, if cooled down suddenly, or slowly but out of contact with air, or shaken up cold in contact with air, is opaque when filtered; whilst the same wort, cooled down on the coolers where it has taken a certain quantity of oxygen into combination, generally passes through the filter very bright. The intelligent brewer is uneasy when this is not the case, for it cannot be denied that the easy clarification of wort has a favourable influence on the easy clarification of beer.

It would, nevertheless, be a grave error to suppose that the clarification of beer must necessarily follow that of wort, and we may be permitted to make a digression here on the subject, to prove this statement.

On February 3rd, 1874, we brewed 2 hectolitres (44 gallons) of beer. The boiling wort, hops and all, was run into a vessel like that represented in Fig. 80, but provided in addition with a false bottom, pierced with holes and fixed at 1 centimetre (0·39 inch) above the true bottom of the vessel; this was meant to retain the spent hops. The temperature of the wort in the vessel after it was filled, February 3rd, 4 p.m., was 90° C. (194° F.), that of the room was 10° C. (50° F.). We permitted the wort to cool down gently, without running cold water over the vessel. The wort indicated a density of 14° Balling.

The following temperatures were taken:—

Temp. of Temp. of
Wort. Room.

Feb. 4, 11 a.m. 38° C. (100·4° F.) 9° C. (48·2° F.)

7 p.m. 30° C. ( 86° F.) 9° C. (48·2° F.)

11.30 p.m. 26·3° C. ( 79·3° F.) 9° C. (48·2° F.)

Feb. 5, 9 a.m. 21° C. ( 69·8° F.) 8° C. (46·4° F.)

12 a.m. 19·75° C. ( 66·6° F.) 8° C. (46·4° F.)

4 p.m. 18° C. ( 64·4° F.) 8·5° C. (47·3° F.)

Feb. 6, 11 a.m. 14° C. ( 57·2° F.) 8° C. (46·4° F.)

Feb. 7, 2 p.m. 11° C. ( 51·8° F.) 7° C. (44·6° F.)

At the end of this time the wort drawn from the smaller tap half-way up the vessel had already become very bright, although it was taken from the bulk of the liquid above the deposit of hops.

On February 8th the temperature of the wort was 9·5° C. (49·1° F.), and that of the room 5° C. (41° F.); the wort was again very bright. Taken from the small tap and tested by Schützenberger’s process it gave no evidence of free oxygen in solution, although its surface was in contact with air. It continued absolutely pure, the arrangements of our vessel, as we have already explained, allowing only such air to enter as was first deprived of its disturbing germs.

Not till February 12th, after we had again determined the purity and brilliant clearness of the wort, a brilliancy which we can compare with nothing so well as Cognac, without the faintest trace of cloudiness, did we set it to ferment in a vessel similar to that in which it had cooled, but without the false bottom. In the process of transfer we effected its aeration by causing it to fall on a small inverted tinned iron capsule some 4 or 5 centimetres (1-½ to 2 inches) in diameter. By this arrangement the wort took up air to the extent of rather more than a third of its saturate capacity, that is to say, by spreading over the capsule, and falling from it in a kind of sheet, it absorbed a volume of oxygen more than a third of the total amount of oxygen which it was capable of absorbing at the existing temperature; this was 12° C. (53·6° F.) at the moment when the wort was drawn off. The pitching was accomplished with a 6-litre flask containing about 4 litres (7·04 pints) of beer that had been in “low” fermentation from February 3rd. The beer was cleansed on February 24th, and had a density of 5-1/4° Balling. We collected 2·345 kilos (75·39 oz. troy) of yeast, containing 56 per cent., that is, 1·313 kilos (42·21 oz. troy) of pressed yeast, containing 36·7 per cent. of yeast dried at 100° C. (212° F.), that is 482 grammes (15·49 oz. troy) for the brew, which would give 241 grammes (7·748 oz. troy) of yeast formed per hectolitre (22 gallons).

The beer was turbid when drawn off, and the small glassful that we removed did not brighten in twenty-four or even forty-eight hours. The samples for some days previously had been in the same condition. The yeast existed as a fine deposit without any straggling yeast about the sides. The want of brightness was dependent rather on spurious colour than on any actual turbidity. We may here remark that if in the preceding experiment the wort had taken up oxygen into combination as well as into solution at the time that it was aerated, the other conditions being the same, the beer would have been bright and better.

It follows from this experiment that a wort may be _perfectly bright_ at the moment when it is pitched, yet fail to produce a beer which shall be bright when racked, or one that will brighten subsequently otherwise than with great difficulty. We may add that when we repeated this same experiment, cooling the wort, however, as rapidly as the conditions of our apparatus permitted, and employing iced water, the beer appeared very nearly bright when it was racked, and brightened pretty quickly in cask and in bottle. The total duration of cooling was not longer than two hours.

The question here arises what part does the oxygen combined with wort play in the clarification of the latter, or in the clarification of beer? Although it may be difficult to give a definite answer to this question, we must bear in mind that in cases where the beer brightens best, if we examine it under the microscope during fermentation, we see, besides the clusters of yeast-cells, floating amorphous particles, which are larger and more compact than those to which the turbidity of worts and muddy beers is due, a circumstance which should lead us to suppose that the oxygen in combination with the wort has the effect of modifying the nature of the amorphous deposit which is produced during the fermentation of the wort. During boiling, the hop yields to the wort a variety of resinous, odorous, and astringent substances, which, for the most part, are held in solution by the presence of sugar and dextrin. At the moment when, under the influence of the yeast, which is itself more or less oxidized, the sugar becomes transformed into alcohol and carbonic acid, a portion of the bitter and resinous matters of the hop becomes insoluble and remains in a state of suspension in the liquid. It is very probable that at this point it is when the combined oxygen assumes its function of modifying the physical structure of these insoluble particles, agglomerating them, so that they become more easily deposited.[179]

Moreover, oxidation tends to form a special precipitate in the wort, which precipitate contributes towards the collection and deposition of the very fine particles suspended in the wort, by a mechanical action, similar to that which we notice in fining operations. On the coolers an effect of this kind is produced. The wort in the copper contains insoluble matters which pass on to the coolers. Very bright when boiling, it grows turbid as it cools, and then contains two kinds of insoluble substances: 1. Substances insoluble alike in the hot and cold liquid, some of which even, as we have just seen, are formed under the influence of heat and air: all these substances precipitating rapidly to the bottom of the vessels. 2. Very fine particles insoluble in the cold, but soluble in the hot liquid, appearing as the wort cools down, and giving it a milky appearance. If the air does not come into play they remain in suspension for an indefinite time, so to say. Wort taken boiling from the copper and cooled down, therefore, forms a considerable deposit at the bottom of the bottles. Now, if we put this wort into bottles without filling them, putting into some only the milky wort from above the deposit, and into others the same wort along with some of the deposit, then raise it to 100° C. (212° F.), and before it has time to cool down shake it up with air a good many times, it will be readily seen that the wort in the bottles containing the deposit will brighten more rapidly and satisfactorily than those in the bottles without the deposit. The deposits which are insoluble in the copper have, therefore, an influence on the clarification. We must add, however, that this influence cannot be compared with that of direct oxidation.

The “turning out” of the wort and its stay upon the coolers to a certain extent exhibit the different conditions which take part in its clarification, inasmuch as the wort charged with its insoluble matters is run off very hot, and with more or less violence against the external air.

§ VI.—Application of the Principles of the New Process of Brewing with
the Use of Limited Quantities of Air.

We have now an idea of the quantities of oxygen which occur, free or combined, in the actual processes of manufacture. We know, moreover, that an excess of air may be injurious, especially to the aroma of the beer, and to that quality which consumers prize so highly, which goes by the name of _bouche_. It must, therefore, be important to ascertain whether in existing processes the proportion of active oxygen may not be excessive.

The best practical means of determining this would consist in comparing the products of different processes with progressively increasing access of air, starting from none at all, as in the case of cooling in the presence of an atmosphere of carbonic acid gas. The following arrangement (Fig. 85) permits us to realize these conditions:—

The wort brought to a temperature between 75° and 80° C. (167° and 176° F.) in the double-bottomed vessel C, passes by the tube _a b_ into a refrigerator, such as Baudelot’s, for example, but acting in an inverse manner to the ordinary mode of using Baudelot’s; that is to say, the wort is made to circulate inside the tubes, whilst the cold water plays on the outside.[180] The wort when cooled, its temperature being indicated by a thermometer _c_, passes down by the tube _c_DD to fill the fermenting vessel A. This vessel is made of tinned iron, or, better still, tinned copper, and has a cover provided with a man-hole and eye-hole; _m n_ one of the tubes for the circulation of air during fermentation; its connecting-tube is not represented, it would be behind the vessel.

At the point _d_ there is a pipe for admission of pure air; this is represented on a larger scale at T. The wort, as it runs through the large tube, carries with it air from outside, and this air is calcined on its way in by means of a flame which plays on the copper tube through which it passes. This arrangement supplies a third or more of the total quantity of oxygen that the wort is capable of acquiring by solution at the temperature at which we work.

F represents the arrangement of the reversed funnel in which the tube _m n_ terminates. Its mouth is closed with cotton-wool held in place between two pieces of wire gauze, for the purpose of purifying the air that enters by it into the fermenting vessel during fermentation.

_v_ is an entrance tap for steam, by means of which the vessel and refrigerator are cleansed from all extraneous germs before each fermentation, and before the wort passes into the refrigerator.

When the fermenting vessel A is at work, we may start a fermentation in a second vessel in the following manner: opening a small tap situated at about a third of the height of the vessel, we pass a few litres of the fermenting beer into a can of tinned copper, previously purified by a current of steam, and filled with pure air. This can is then emptied into the fresh vessel, an operation of no difficulty, since we have merely to connect the tap of the can with the small tap of the vessel, and lastly, the vessel is filled with wort, which then mixes with the fermenting liquid. These various manipulations, it is evident, are performed under conditions of complete purity, without the slightest contact of the liquids either with the exterior air or with utensils contaminated by disturbing germs.[181]

It is seldom that an industry adopts at once in their entirety new practices which would necessitate a re-arrangement of plant, and the process of which we are speaking would require such re-arrangement, as far as the fermenting vessels and the method of cooling the wort are concerned. The new process would, however, be of great value if once introduced, simply for the manufacture of pure ferment and pure wort, or even for that of pure ferment alone. In other words, we might retain the ordinary methods employed in low fermentation, use the same method of cooling or the new one, the same fermenting vessels, and the process of fermentation at low temperatures; the yeast, however, would be prepared in a state of purity in the closed vessel which we have described, collected in those vessels, aerated, and then employed after the old-established custom; better still, the pitching might be performed with beer in the act of undergoing pure fermentation.

Above the fermenting-stage there might be arranged a room for the vessels used in the new process, from which the pure beer could be run for pitching purposes into the large tuns in the brewery below. It is true that beer prepared in this manner would not be perfectly pure, but from the results which have been obtained by working on this system, there is no doubt that it would possess keeping qualities far superior to those of beer made with ordinary yeast, even supposing that beer to have been treated with every possible precaution, and to be as pure as any produced in the best regulated breweries.

In the month of September, 1874, we conducted an experiment at Tantonville, in a closed vessel capable of holding 6 hectolitres (132 gallons). The deposit of yeast served to pitch an open vessel, the wort of which had, moreover, been cooled under conditions of purity. The cooling had been effected by means of the Baudelot refrigerator, represented in Fig. 85, the wort in the closed vessel having been similarly treated. For shortness sake, we may designate the closed vessel and its beer by the letter K, and use the letter M for the open vessel and its beer, and T for the corresponding beer of the brewery. The vessel K was pitched on September 4th, and racked on September 17th, the beer then showing a density of 5·5° Balling.

The beers K and M were sent to Paris at the same time as some barrels of the beer T, brewed by the ordinary process; and samples of these different beers, which arrived on October 22nd, were procured from five different cafés for purposes of examination.

The beer M did not suffer by comparison with the beer T. The similarity between the flavours of these two was so close as to puzzle even experienced judges. In both cases the beer was brilliantly clear. In two cafés the beer M was even preferred to T, being considered softer on the palate (_moelleuse_) and of more decided character (_corsée_) than T, a circumstance which may be explained by the fact that its wort had been less aerated.

The beer K, although very clear and bright, was considered inferior to M, but the sole reason of this was that at the date when it was tasted—November 3rd—it did not froth. As we have already remarked, a peculiarity of the beers made in closed vessels is that their secondary fermentation takes a longer time to develop. The yeast held in suspension in the beer, at the moment when it is drawn off, is, in the case of all beers, the yeast of a supplementary fermentation, if we may use that expression. In the ordinary process of brewing, this yeast, in consequence of the greater aeration of the wort at the commencement of fermentation, is more active, or, rather, more ready to revive and multiply than is that which develops in closed vessels. If the barrels of the K beer had been tapped on the 12th or 15th of November, instead of on the 3rd, it is probable that they would have contained as much carbonic acid gas as the beer M contained at the earlier date. This delay in the resumption of fermentation, which characterizes beer made in closed vessels, is an advantage, inasmuch as it facilitates the transmission of the beer to long distances, besides giving us the smallest deposits of yeast in cask or bottle, as we have already pointed out.

In comparing the keeping qualities of the beer M and the beer T (the latter being the brewery beer), we made the following observations:—[182]

On November 25th we began to detect in the brewery beer an unsound flavour; a large deposit, too, had formed; the beer had lost its brilliancy, and frothed enormously. The deposit swarmed with diseased ferments, especially those represented in Nos. 1 and 7 of Plate I. The beer M, on the contrary, was in brilliant condition, with an insignificant deposit, and an ordinary froth, if anything, rather small, and beautifully bright.

On December 3rd the beer M was still good, very clear, and in excellent preservation; it was considered by professional brewers as remarkably sound.

December 22nd, the same beer M was still very bright and good.

January 20th, the beer was still bright; for the first time, however, we detected in the deposit in the bottles, which was still small, the filaments of turned beer. This unsoundness was in its earliest stage. Now, comparing the relative unsoundness of the two beers, we see that M kept at least two months longer than the corresponding brewery beer. This example shows us that as far as the keeping powers and the quality of beer are concerned, the existing process would gain considerably by the employment of pure wort and pure ferment; and, indeed, it seems likely that the new process may be introduced into breweries with this object in view.

In the course of the summer of 1875 we made the following observations on the keeping qualities of a beer brewed on the new system, all the details of which had been rigorously carried out. The beer brewed at Tantonville during the months of June and July, at a temperature of 13° C. (55·4° F.), in 50-litre and 80-litre casks (11 and 18-gallon), had been sent by slow trains to Arbois (Jura), where we were staying for a time. The temperature of the wine cellars in which these barrels were stored was, on June 1st, 12·5° C. (54·5° F.); this rose gradually until September 1st, when it attained 18° C. (64·4° F.). In this cellar the brewery beer, brewed in the ordinary way, underwent change in the course of fifteen days or three weeks, whilst the beer brewed on the new system remained sound for several months. It is true that some of the barrels lost their frothiness, and that the beer in them underwent a peculiar vinous change, but these effects in no way depend on the conditions peculiar to the new process.

Comparing the beers K, M, T, of which we have been speaking, we see that, however useful the aeration and oxidation of the wort may be in quickening fermentation and facilitating clarification, yet it is by no means indispensable to the success of our operations that we should introduce into our worts large quantities of oxygen, whether by solution or combination. Beyond a certain limit—a limit which is undoubtedly overstepped in the existing process—oxygen is injurious to the palate characteristics and aroma of beer.

These comparisons have proved to us that the new process can be applied to wort aerated to the third of its saturate-capacity for oxygen, and pitched with a good “low” yeast, taken from the fermentation of a wort aerated in the same way, and that the beers thus obtained not only possess vastly superior keeping properties, but are equal in quality and superior in palate-fulness to beers brewed with the same wort on the existing system. We should be perfectly justified in forming this conclusion as to the _strength_[183] of the beer furnished by the new process, even if on tasting it we found that the new beer M was merely equal in strength to Tourtel’s beer brewed in the ordinary manner, since the wort in the new process, other conditions being the same, is weaker than the same wort treated in the usual way, from not having undergone that evaporation on the coolers which concentrates it. If we were to restore to the concentrated wort of ordinary brewing all the water lost by it through evaporation, the beer that we should obtain would be sensibly weakened.[184]

One thing, however, is that we must employ good varieties of “low” yeast. We have seen how the employment of certain forms of yeast renders the clarification of beers difficult, as well as extremely slow, and almost prevents their falling bright at the end of fermentation. These yeasts, moreover, frequently impart to beer a peculiar yeast-bitten flavour, which does not disappear even after a prolonged stay in cask. Even repeated growth of these yeasts, whether in closed or in open vessels, and no matter what quantity of air we may supply them with before fermentation, seems to have no effect in changing their character. The only thing we can do with these varieties of yeast is to get rid of them with all speed, and to replace them with others.

Notwithstanding the comparative success that has attended various trials of the new process on the commercial scale, that process has not yet been practically adopted: and here we must bear in mind that we have not to deal with any casual invention or mechanical improvement that could be introduced all at once into the working of a brewery; we are dealing with operations of considerable delicacy, which necessitate the adoption of a special plant to carry them out. Under such conditions time and labour are required to effect a change in the established processes of a great industry. This, however, cannot diminish the confidence that we have in the future of our process, and it is our hope that the same confidence will be shared in by all those who may give this work an attentive perusal.

Footnote 162:

M. Galland, a brewer in Maxéville, near Nancy, published with his
name, in November, 1875, a pamphlet, which was reproduced in the
brewing journals of that date, bearing the title, _It is said, “the
air being impure, let us exclude it;” I say, “The air being impure,
let us purify it.”_ These two aphorisms, together or apart, constitute
the essential novelty of my researches on beer, and M. Galland is
mistaken in attempting to appropriate the merit of the second
alternative (see my note in the _Comptes rendus_ of the 17th November,
1873, and the text of the letters-patent obtained 13th March of that
year). M. Galland has devised some arrangements for putting the latter
of these two schemes into practice; but it is possible, of course, to
effect this in a variety of ways. M. Velten, a brewer in Marseilles,
had already accomplished this in his efforts to carry out practically
the procedure advocated in the present work.

Footnote 163:

[Non-technically, stirred about.—ED.]

Footnote 164:

As stated in the paragraph on aërobian ferments, in Chapter V., “low”
yeasts, to be preserved in their state of “lowness,” must be submitted
to often-repeated growths—every fifteen days in winter and every ten
days in summer, that is to say, they must be grown afresh after each
of these intervals. If this is done, there will be no reason to
apprehend the formation of aërobian ferments, which, as we have stated
before, may embarrass us by transforming our “low” yeasts into “high”
yeasts.

Footnote 165:

It has been observed by brewers that, sometimes, without any apparent
cause, a yeast suddenly becomes inactive and fermentation ceases.
Accidents of this kind may probably be explained in the same manner as
the facts of which we are speaking. If a wort has not been aerated, or
if it has been deprived of oxygen by a commencing development of
microscopic organisms, the yeast formed in it will be very inferior,
and the fermentation may stop at its commencement or soon afterwards.
In such a case, an aeration of the yeast and wort would be the best
remedy.

Footnote 166:

PASTEUR, _Comptes rendus de l’Académie des Sciences_, vol. lii. p.
1260, and _Études sur le Vin_, 2nd Edition, p. 277.

Footnote 167:

We may here remark that the system of gutters in the above apparatus
is much simpler than that described in connection with Figs. 76 and
77. The water which falls on the cover is carried off, when the gutter
is full, by a circle of grooves, inclined so that the streams running
from them meet and form more readily a sheet of water, which flows
over the exterior surface of the cylindrical vessel.

Footnote 168:

[It will be well for the reader to bear in mind, that the word
“strength,” used by Pasteur many times in this chapter, has a
different meaning to that which attaches to it in the minds of English
brewers, who in nearly every case use it in reference to _original
gravity_, while the author employs it, in this chapter, at any rate,
to denote the _palate characteristic of strength_, in other words
_palate-fulness_. For this reason we have thought it best in many
cases to actually substitute the term “palate-fulness,” or “body,” for
the literal translation of the French word “force.”—F. F.]

Footnote 169:

[As some confusion has existed in the nomenclature of these salts, it
may be as well to offer some explanation.

The salt here used for absorbing oxygen was discovered by
Schützenberger, and named by him _hydrosulphite of soda_. It no longer
now goes by that name, being called _hyposulphite of soda_, NaHSO_{2}.

The salts formerly known as _hyposulphites_ are now called
_thiosulphates_, as Na_{2}S_{2}O_{3}.

Thus to put them together we have:—

Hyposulphite (Hydrosulphite) NaHSO_{2}
Bisulphite NaHSO_{3}
Thiosulphate (Hyposulphite) Na_{2}S_{2}O_{3}

The thiosulphates were formerly regarded as containing the elements of
water in their composition, thus:—Na_{2}H_{2}S_{2}O_{4}, which being
halved would give NaHSO_{2}, isomeric with hyposulphite, as Pasteur
says. It is further to be observed that Pasteur uses the old notation,
in which the number of atoms of sulphur and oxygen are the double of
what they are in the new.—D. C. R.]

Footnote 170:

SCHÜTZENBERGER, _Comptes rendus de l’Académie des Sciences_, vol.
lxxv., p. 880.

Footnote 171:

M. Schützenberger applies the term _saturated_ to a solution of
hydrosulphite prepared thus, or very nearly so; a current of
sulphurous acid is passed through a solution of commercial bisulphite
of soda, to excess; 100 c.c. (3-½ fl. oz.) of this solution and 30
grammes (46 grains) of zinc filings are put into a small flask, so as
to completely fill it; the bottle is corked up and the mixture is
shaken briskly for about a quarter of an hour. Lastly, the contents of
this flask are poured into a large 2-litre flask, with water and
containing milk of lime, prepared by mixing 100 grammes (3·2 troy oz.)
of quicklime in the water just before it is used. The whole is shaken
briskly for some minutes and then left to settle. The supernatant
liquid soon becomes bright. This is the hydrosulphite; but in this
state it is too concentrated; and should be syphoned into another
2-litre flask half full of water. In the alkaline condition this salt
absorbs gaseous oxygen much less rapidly than in the acid, so that the
liquids will retain their strength much longer, if they are kept in
well-corked bottles.

Footnote 172:

The numbers _n_ and _n´´_ will vary as the wort, or liquid which we
have to test, is perfectly neutral or otherwise. Should it be acid
_n´´ n_, should it be alkaline _n n´´_. This would be a very exact
method of estimating the acidity or alkalinity of any coloured liquid.

Footnote 173:

[The Balling saccharometer being almost unknown in England, we may
explain that its indications are for percentages of sugar in
saccharine solutions, or of extract in worts; 17·9° Balling,
therefore, means 17·9 per cent. of sugar or extract in the respective
liquids.—F. F.]

Footnote 174:

Experiments made, at our request, by MM. Calmettes and Grenet, at
Tantonville; in Tourtel’s brewery.

Footnote 175:

See foot-note, page 367.

Footnote 176:

[For non-technical readers we may explain the expressions “gathered,”
here used, and “turning out,” used on page 365. “Turning out”
describes the operation of emptying the _copper_ contents into the
_hop-back_, or the _hop-back_ contents on to the _coolers_.
“Gathering” refers to the time when the worts are finally intermixed
and _weighed_, prior to the commencement of vinous fermentation.—F.
F.]

Footnote 177:

We know also from the direct experiments of M. Schützenberger,
performed on aerated water with which yeast had been mixed, that yeast
causes all the oxygen in solution to disappear very quickly, so that
hydrosulphite gives no evidence of a trace. (See SCHÜTZENBERGER,
_Revue scientifique_, vol. iii. (2), April, 1874).

Footnote 178: