By L.A. Enzinger
From The Brewers’ Guardian – 1883
The turbidity occurring both in worts and in finished beer may be ascribed to a variety of causes, and it may not prove uninteresting if we subject the substances capable of causing such turbidity to a brief observation.
1. ALBUMEN COAGULABLE BY BOILING. If worts that have been “tapped” perfectly clear, are brought up to boiling point, they will become turbid when heated, and even before reaching the boiling point. The turbidity is caused by the transformation through heat of an hitherto soluble into an insoluble substance, and in such fine particles that their form is imperceptible to the unaided eye. If the boiling be long continued, the separated particles form a flocculent coagulation of an albuminous substance, which we specify by the title of “albumen coagulated by boiling” (coagulable vegetable albumen), or albumen. The greatest diameter of these flakes varies between 0·0067 – 0·0250 mm, their minimum diameter, on the other hand, between 0·0014 – 0·0015 mm.
The appearance of this coagulation, the separate flakes of which may easily be recognised with the naked eye, is called in mashing the “separation” and also the “break.” The separated particles form the principal constituents of the slimy mass found on the surface of the grains when the worts have run of (called in German “oberteig”). As in the majority of the decoction brewing processes now practised, there is always a certain quantity of mash left which has not been boiled; the worts from this mash will be found when in the copper to contain small quantities of albumen in a soluble condition, and these are necessarily separated during boiling.
If the running off has been carelessly performed, a portion of the coagulation separated during mashing will also reach the copper, and will with that already present be later deposited on the floor of the cooler in a turbid precipitate as a constituent of the well-known cooler sediment.
Where the infusion process is employed in mashing the albumen does not remain in the mash-tun as an “oberteig,” but arrives in the copper in undiminished quantity, where it is coagulated in boiling, and afterwards deposited as a turbidity on the cooler. Where the infusion process is used, considerably more albumen coagulated by boiling is found in the cooler sediment than accompanies the decoction process. Only by employing a process in which the whole mash is heated to boiling, can the entire amount of albumen be retained in the mash-tun, provided that the tip has been properly conducted.
2. TANNATE OF ALBUMEN. If we expose a beer-wort, after the albumen has been coagulated by boiling and removing by filtration, to the action of a clear hop extract, a marked turbidity of the worts will immediately follow. This turbidity will be caused by the combination of the tannic acid, contained in solution in the hop extract, with a certain quantity of the soluble albumen of the worts, to form an insoluble substance, which on prolonged boiling assumes the appearance of a coarse, flaked coagulation, and which is designated tannate of albumen. This tannate of albumen forms the “break” or “separation” which occurs at the conclusion of the boiling of the worts with hops, and is composed of larger particles than the albumen alone. Their largest diameter amounts to between 0·0050 to 0·0056 mm, the smallest diameter 0·0020 to 0·0026 mm. This substance forms the largest portion of the cooler sediment.
> Editor’s note – “glutine” is an old spelling variation of “gluten”)
3. GLUTINE. If perfectly clearly tapped wort or hopped wort, from which the coagulation has been removed by filtration in a heated state, be allowed to cool, either of the two fluids will increase in turbidity as the cooling progresses. The cause of this turbidity is the presence of a substance that has the property of being soluble in heated but insoluble in cold fluids; it is designated glutine. If the cooling of the un-hopped or hopped wort has been carried forward as far as possible, it assumes the appearance of a clayey or foxey clouded fluid. Even the closest observation cannot distinguish the formation of the minute bodies which cause the turbidity, with the naked eye, and even with a microscope it is only possible by using the highest powers to see the separate glutine particles. The separated particles of glutine have a diameter of from 0·0009 to 0·0014 mm. They may be distinguished under the microscope from coagulated albumen, or tannate of albumen, by the fact that instead of appearing in irregular forms, as do the latter, they appear as very small solid spherical bodies of a dark colour. If we collect a large number of glutine globules on a filter paper, they will form a dark brown, shining residue, while coagulated albumen, or tannate of albumen, form a yellowish grey residue.
If beer wort that has become very much clouded be warmed to the temperature at which it has been drawn from the copper or the mash-tun perfectly clear (100° or 70° C respectively), it will become clear again. The glutine bodies, which were the cause of the turbidity, have become dissolved as soon as the rise in temperature has occurred. If we again cool the cleared worts, cloudiness will again be caused by separation of the glutine.
Beer worts, according to the quality of malt used in their production, contain widely varying quantities of glutine. If a wort be brewed from malt which has been produced from a barley very rich in starch, and if in this malt a thorough porosity or opening has been secured by a vigorous development of the root and leaf germs, such a wort, in some instances, is capable of becoming saturated with glutine at 75° C and at the same time dissolving all the glutine present in the malt. The worts will appear perfectly clear at 75° C, and can, after having been heated to boiling, be reduced to 75° C again, without any separation of glutine occurring. Only when the temperature passes below 75° will the glutine globules separate from the wort, which has been saturated with glutine at this temperature, and only then will it render its presence apparent by causing turbidity.
If a barley is used for malting that is rich in glutine, it can happen that, in spite of the well-advanced development of the leaf and root germs, there will be sufficient glutine present to saturate the worts at the boiling point. The mash will in that case show a break after boiling, and allow the wort to appear clear, but if it cools off only a few degrees, a turbidity will be caused by the separation of glutine. If we pump the clear-boiled thin mash back into the mash-tun, or if we allow it to pass the period allotted for it to stand, the reduction in temperature to 70° – 75° C will be fully sufficient to separate so much glutine as to give the worts a turbid (dim, dull, or clouded) tap, for the infinitely small particles of glutine will filter through the mash-goods, or will even be separated under the false bottom and in the pipes, by the cooling that will take place there.
If in malt made from glutinous barley, the root-germ is too weak or the leaf-germ insufficiently developed, the result will be that the worts produced from such a malt will be over-saturated with glutine at the boiling point, and will be entirely unable to take up all the glutine from the malt. The mashes in such a case may show a coarse-flaked break, but the wort, even at the boiling point, will be clouded by undissolved glutine.
Such worts will, as understood, run off very cloudy, will have a red appearance and marked turbidity on cooling.
Glutine, according to these statements and with respect to its character, shows a marked resemblance to such bodies as crystallise from fluids. The worts, once saturated at a certain temperature, can take up no more glutine, although it may be present in abundance; just as water, saturated with sugar can absorb no more, even though it be added. If water be saturated with sugar while boiling, during the continuous cooling of the solution, sugar will be separated in the form of crystals of a definite size and shape; so it is with glutine, which is always separated in the form of a small, sharply defined globules. If crystallisation is disturbed by movement of the fluid in cooling, the sugar crystals are saturated as smaller bodies; glutine shows the same property in such a case, by the varied sizes of its globules. Rapid or slow cooling is also of importance in the complete separation of crystals.
If, for instance, a saturated sugar solution at 12° C contains still undissolved sugar, a portion of the sugar may be removed by setting up a fermentation in the sugar solution, which will effect the solution of as much of the undissolved sugar present as has been decomposed in the fermentation.
If a beer wort is set at a temperature of 12° C, there will be about 10 per cent of the glutine present in it in a dissolved condition, about 90 per cent of the glutine will swim in the worts in the form of small globules in a separated condition. During the fermentation the yeast is capable of taking up a portion of the dissolved glutine as nourishment, employing it partly for its own nourishment, partly in the production of new yeast generations. As soon as in this manner the wort has been made poorer in dissolved glutine, therefore is no longer saturated with it, it will continue to dissolve a portion of the glutine globules present in an insoluble condition in the worts until, according to the existing temperature, it has again become saturated with glutine.
4. FERMENT OF LACTIC ACID. If we set a glass of hopped or un-hopped beer wort, filtered perfectly clear after cooling, in a place showing ordinary atmospheric temperature, it is possible already within twenty-four hours to perceive, that although the temperature has remained equable, a change has occurred in the wort. It will have become slightly clouded and no longer have a sweet taste, but a peculiarly sour flavour, the turbidity becomes more marked as time elapses and the sour flavour perceptibly increases. The cloudiness is caused by an immense number of rod-shaped bodies of 0·0009 to 0·0028 minimum diameter and a length of from 0·0013 to 0·0316 mm. Under the most powerful magnifying apparatus, these bodies do not appear, as when slightly magnified, in the form of long cells, they are distinguished from the latter by their independent movement. Like worms they bend and twist slowly, often to such an extent that their two ends almost touch. They are distinguished by the title of ferments of lactic acid fermentation; in the course of their development a product is formed that we style lactic acid.
The conditions under which lactic acid is instituted in the worts in the absence of the organisms, are always the presence of atmospheric air and a suitable temperature. At a temperature near freezing point, or above 75° C, lactic acid fermentation no longer occurs; between 20° and 40° it occurs very easily and progresses with great rapidity, and our surprise is excited by the extraordinary number of organisms newly formed in a short period. The presence of carbonic acid instead of atmospheric air, or of alcohol in the beer worts, retards the active development of the ferments of lactic acid fermentation, and for this reason, the worts immediately after cooling must be exposed as quickly as possible to alcoholic fermentation if it is desired to avoid lactic acid fermentation. The vessels which serve for transporting or storing the worts, or the apparatus with which the worts come in contact – for instance, wooden vessels, piping, filters, coolschiffe and coolers – must be carefully treated, as through uncleanliness in these objects the appearance of lactic acid fermentation rapidly occurs.
5. FERMENT OF ALCOHOLIC FERMENTATION – If to clear-filtered worts a small amount of yeast be added, there will be an immediate clouding of the worts. On closely observing the sample in a small test-glass, the cause of the turbidity, viz., the separate yeast cells, will be apparent to the naked eye. The wort looks as though a number of little grains of sand were swimming around in it, while between the sand-grains it is perfectly bright. Yeast cells, the ferment of alcoholic fermentation, assume sometimes a spherical, sometimes an ovoid appearance, and are of various sizes. The smallest round yeast cells have a diameter of 0·0050 mm, the smallest oval yeast cells have as their minimum diameter 0·0065 mm, the largest round yeast cells have a diameter of 0·0100 mm, while the largest oval yeast cells are found up to 0·0123 in length and 0·0074 in minimum diameter.
Healthy, vigorous yeast cells have contents of a uniform nature, without hollow spaces or granulated characteristics, only diseased or polluted yeast appears as though it were not internally uniform. The yeast cells nourish themselves on the substances in solution in the beer worts, suspended (un-dissolved) substances cannot be assimilated by the yeast. Nourishment is taken in by the entire surface of the yeast cell, easiest, therefore, when the cells are floating in the fluid worts. If insoluble substances attach themselves to the worts in large quantities, the absorption of nourishment cannot take place in the contact surface, and either in its absorption of nourishment, or in its multiplication, the progress of the yeast will be retarded.
The multiplication of the yeast cells occurs by the formation on the side of the cell (the mother-cell) of a projection, the so-called daughter-cell, which continues to increase and divide itself from the former as soon as it has become independent, i.e., of the same size as the mother-cell, and possessed of the ability to absorb nourishment from the worts, to grow and to increase. The most vigorous development and increase of the yeast goes on most completely when suitable nutritive substances (carbohydrates, protein substances, and mineral substances) are present in sufficient quantity and in the right proportion, when a temperature favourable to the growth of the yeast is uniformly observed, and when care is taken that other ferments (ferments of lactic acid fermentation, putrefactive substances, evil-smelling gases, impure air, &c.) are kept remote from the worts. The greatest cleanliness is therefore to be observed, especially in the vessels in which the cooling, the transportation, and the pitching of the worts with yeast take place, because in these stages they are most susceptible of damaging influences.
If the yeast cells in the beer worts do not find the nourishment they require in sufficient quantity, or if the conditions under which the nourishment is easily assimilated are not fulfilled, they are injured in their growth, and produce, should they be so fortunate as to be capable of reproduction, new generations, whose miserable appearance and small size show that they have been produced under unfavourable circumstances. These ill-nourished yeast cells continue to swim around in the beer after the chief fermentation has reached its end, and on the casking of the beer they enter the lager casks, in which they are either deposited after a long time, and in this case the beer becomes bright, or remain floating in suspension, so that yeast-clouded beer is caused.
6. FERMENT OF ACETOUS ACID FERMENTATION. – The beer in the store casks is, while on storage, in a condition of slow after-fermentation, which will last so long until the beer is sent out. During this time, a complete clarification of the beer by deposit of the yeast cells must have taken place. Seen through the bung-hole, the beer should not appear black, but as though covered with a delicate white foam. As long as this white foam, which is to be regarded as a sign of progressing alcoholic fermentation, is present on the beer, the carbonic acid developed by the fermentation, being heavier than the atmospheric air, forms a protective covering against the oxygen in the cellar atmosphere. A reduction in the volume of this foam points to the approaching conclusion of the after-fermentation in the cask, in which case the beer may soon become a prey to destruction. A short time before the conclusion of the secondary-fermentation in the cask, only a large bubbled foam is visible through the bung-hole; the beer in a test-glass appears perfectly clear. If this head commences to disappear, we shall notice the fact that the beer begins to lose its brilliancy, becomes turbid and clouded, and grows more turbid from day to day.
The cause of this clouding is the development of the ferments of acetous acid fermentation. It is either already present in the beer, but has been retarded in its development by the carbonic acid, or it has only been introduced through the atmosphere into the beer, and in consequence of the now prevailing circumstances which have allowed the access of the oxygen, it has developed.
The surface of the beer, by continued development of the acetous acid, is covered with a skin (mother), at first thin but constantly increasing in thickness, which is formed of the rapidly growing vinegar fungus. A part of the vinegar fungus separates from the skins, and sinks to the bottom of the beer, and soon the entire bulk will be clouded by it.
The organisms of acetous acid fermentation are smaller than alcohol yeast, and consist of longish cells, that branch out more or less or arrange themselves in rows: they increase, like the organisms of alcoholic fermentation, by budding and separation of the newly-formed cell, and it frequently happens that several cells will remain for a considerable time attached together, and only isolated ones will become separate.
Beer which is clouded only by the ferment of acetous acid fermentation should appear like yeast-clouded beer; it differs eminently from the latter because, besides the acetous fermentation, other fermentations, especially lactic acid fermentation, and similar phenomena of decomposition occur.
7. HOP RESIN. – If a hopped wort filtered while as cold as possible to the greatest degree of clearness, be set to ferment, kräusen will be formed, at first snow white, but they will soon assume a brown appearance and at the same time acquire a bitter flavour. The brown colour of the kräusen comes from a substance that was in solution in the worts when pitched, but which has become separated during the fermentation. This substance is the so-called hop resin which was dissolved by the worts (itself a solution of sugar or maltose), during the boiling with the hops, but which during the fermentation is again separated to exactly the same extent, as the de-composition (fermentation) of the sugar solution (maltose -solution) progresses. With the hop-resin is also eliminated a proportion of the bitter flavour of the hops, hence the bitter taste of the brown kräusen. The hop-resin separates in lumps of a brown colour, partly on the surface of the beer, assuming the form of a cover as the termination of the chief fermentation, or it sinks to the bottom of the fermenting tub and contributes largely to the contamination of the sediment.
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