A Practical Treatise on Brewing/Appendix/Diastase
DIASTASE.
Little more has been elicited of the nature and powerful action of Diastase in the mash-tun, since our first publication. The minute directions given as to the first mashing temperatures, are calculated to secure as perfect and sound an extract, as the action of Diastase can produce. If, therefore, the indications before mentioned be shown, we may rest satisfied that as good an extract has been made as the malt used can possibly produce, at least in sound wort. If the indications do not take place, it must proceed either from bad manipulation, or the inferiority of the materials used. Having thus endeavoured to put an end to all mystery on this most important subject, we here insert our article on Diastase from the First Edition.
The researches of the French chemists last summer (1834), will shed a new light on the nature and properties of malt, and the mode of extracting. Starch is described as consisting of minute particles, like granules, each of them included in a skin or cuticle, a thick, slimy, gum-like body, and therefore resembling somewhat the structure of seeds. To the internal contents of these granules, M. Biot gave the name dextrin; it might also be called starch-gum, because in its properties it is quite analogous with the latter. The skinned integument, including the dextrin, prevents the starch from coming forth; for starch is not soluble in cold water. But by breaking the cuticle this is accomplished, and gum produced from starch, or rather gum contained in starch, is made free.
For attaining this, the following means are at present known.—1. Boiling. The more such particles are torn by the heat, the more of the gum is dissolved; and the more particles of starch are preserved in the fluid, the more paste-like remains the latter.—2. Roasting. In both cases, the heat partly tears and partly annihilates the cuticles. This case sometimes occurs in kiln-drying.—3. Treating it with some acid fluid.—4. Treating it with malt, which, in a manner not yet known, by a substance contained in it (diastase), has the power of lacerating the cuticles of the starch granules. The diastase contained in malt is said to be a solid, white, tasteless, uncrystallised body, soluble in water, but insoluble in alcohol. Dissolved in water, it turns sour very soon. Its most remarkable property is, that one part of it is sufficient to tear, or burst open, 2000 parts of potatoe starch diluted by 8000 parts of water, by which means its dextrin becomes free, and its insoluble cuticles are either precipitated or made to swim on the surface. Diastase is produced by diluting malt-meal, or bruised malt, in cold water, filtering the fluid, and heating it: it becomes turbid, and some substance resembling white of eggs is precipitated: strain again, and add absolute alcohol (free of water), whereby the diastase falls to the bottom, while the sugar which was in the malt remains dissolved. It is then dried by a low heat, because a higher one would decompose it. The heating of the solution is not necessary: or the diastase may be separated by the mere action of alcohol. Diastase, produced in the above manner, is not quite pure, still containing some azotic substance, which may be removed by a repeated digestion of the product by water, and precipitation by alcohol. In seeds, which have undergone germination, it is contained in the immediate neighbourhood of the blade, but not in the rootlets; By the boiling-heat the diastase loses the power of converting starch into gum and sugar: this therefore, is the substance by the action of which saccharification takes place in the mash-tun.
This completely accounts for an almost instantaneous change of colour in the extract, which invariably takes place in the mash-tun during the first mash, when the heats are properly taken.
If, therefore, this change of colour do not take place, we may rest assured that our mashing temperature is wrong.
It also proves what has been already stated in the foregoing pages, that nearly the whole of the extract is made in the first mash, and that all we do afterwards is merely washing out that which remains of the extract in the grains.
It also shows the importance of taking our first mashing temperature properly. By the boiling temperature, say the French chemists, the diastase loses the power of converting starch into gum or sugar. Thus setting the goods in the tun.
It may be possible that a considerably lower temperature than the boiling may have the same effect of destroying the power of the diastase; indeed we know that it does so, as goods have often been set at much lower temperatures than boiling. As already stated, therefore, under the head of Mashing, we should rather turn on the first liquor too low than too high; for too low a temperature may be corrected in the after process, whilst, on the other hand, we now have it distinctly pointed out to us, that too high a temperature is destructive.
This discovery of the French chemists may also lead to other very important results in the formation of extracts; but as it has only been pointed out to me by a friend since writing the foregoing pages, we are neither of us altogether prepared to give the results of any practical observations we have as yet made upon the subject. I know, however, that my friend, already mentioned, Mr. Robert Stein, had, long ago, ideas as to the formation of extract, which this new discovery appears completely to confirm.
There can be no doubt that a peculiar change takes place in barley during the process of its being manufactured into malt, which change is absolutely necessary for the conversion of the starch of the grain into saccharine matter in the mash tun; but what this change really is, or how it is effected, remains still a matter of doubt. It was at first supposed, as stated above, that it was a certain component part of the malt, which, by chemical means, might easily be separated from it, and might per se be made available for other purposes. This opinion, however, is now losing ground, and chemists begin to doubt whether diastase as a separate principle really exists; at all events, it is in quantities so small as to be but very rarely seen, and such a substance is now hardly known, nor is it to be obtained at the present time even in Paris, where the discovery is said to have been made. I have been favoured with the following opinion of diastase by a scientific friend who has made some experiments on the subject.
"The gluten of all grain is known to be particularly prone to spoil or undergo decomposition when wet, and this decomposition passes through several stages, ending in complete putrefaction. In these different points of its progress to putrefaction, the gluten of barley and other grains acts as a ferment, but with different results in the early, from what it produces in the late stages. It is only in the first stage of decomposition that gluten saccharizes, and it is in this state in barley which has been moistened and begun to germinate. Yeast is still only the same gluten, but farther decomposed; it is then capable of decomposing saccharine matter, and resolving it into alcohol and carbonic acid, that is of producing the vinous fermentation. Diastase, therefore, is a peculiar condition of the glutinous part of malted grain rather than a distinct principle; the name, however, is still retained in this sense by chemists, as being a convenient term for certain purposes." My friend, Mr. Maugham, also, some years ago, at my suggestion, made some experiments in respect to diastase; and he afterwards stated to me that there is no such thing as diastase as a distinct principle.
Of its actual effects in the mash-tun, we know very little more than when it was first discovered, being merely that some peculiar change is effected in barley in the process of malting, without which but very little saccharine extract can be obtained. Corn-distillers also cannot get an extract without a mixture of malt.
We know also that a certain temperature is requisite to be acquired in the mash-tun before the extract can be thoroughly formed, and that going beyond this temperature may do harm, but cannot be of any benefit. When the proper temperature is gained, an almost instantaneous change takes place in the appearance of the mash, so perceptible to any one at all acquainted with the process as fully to point out to him that his object is now attained. He also knows that very little further manipulation on his part is either useful or beneficial—and I can assure him that a few degrees up or down in the temperature of the mash, when running off from the tun (upon which so much is sometimes thought to depend) will be of no material importance. He may be certain that the proper chemical change has taken place for ultimately producing the best beer; let him not then, by a mistaken avarice, in carrying the process too far, run the risk of counteracting, by any addition of that which may be injurious, the proper effects of that extract which has already been so well prepared.