1911 Encyclopædia Britannica/Brewing/Chemistry
V. BREWING CHEMISTRY.
The principles of brewing technology belong for the most part to physiological chemistry, whilst those of the cognate industry, malting, are governed exclusively by that branch of knowledge. Alike in following the growth of barley in field, its harvesting, maturing and conversion into malt, as well as the operations of mashing malt, fermenting wort, and conditioning beer, physiological chemistry is needed. On the other hand, the consideration of the saline matter in waters, the composition of the extract of worts and beers, and the analysis of brewing materials and products generally, belong to the domain of pure chemistry. Since the extractive matters contained in wort and beer consist for the most part of the transformation products of starch, it is only natural that these should have received special attention at the hands of scientific men associated with the brewing industry. It was formerly believed that by the action of diastase on starch the latter is first converted into a gummy substance termed dextrin, which is then subsequently transformed into a sugar—glucose. F.A. Musculus, however, in 1860, showed that sugar and dextrin are simultaneously produced, and between the years 1872 and 1876 Cornelius O'Sullivan definitely proved that the sugar produced was maltose. When starch-paste, the jelly formed by treating starch with boiling water, is mixed with iodine solution, a deep blue coloration results. The first product of starch degradation by either acids or diastase, namely soluble starch, also exhibits the same coloration when treated with iodine. As degradation proceeds, and the products become more and more soluble and diffusible, the blue reaction with iodine gives place first to a purple, then to a reddish colour, and finally the coloration ceases altogether. In the same way, the optical rotating power decreases, and the cupric reducing power (towards Fehling's solution) increases, as the process of hydrolysis proceeds. C. O'Sullivan was the first to point out definitely the influence of the temperature of the mash on the character of the products. The work of Horace T. Brown (with J. Heron) extended that of O'Sullivan, and (with G.H. Morris) established the presence of an intermediate product between the higher dextrins and maltose. This product was termed maltodextrin, and Brown and Morris were led to believe that a large number of these substances existed in malt wort. They proposed for these substances the generic name "amyloins." Although according to their view they were compounds of maltose and dextrin, they had the properties of mixtures of these two substances. On the assumption of the existence of these compounds, Brown and his colleagues formulated what is known as the maltodextrin or amyloin hypothesis of starch degradation. C.J. Lintner, in 1891, claimed to have separated a sugar, isomeric with maltose, which is termed isomaltose, from the products of starch hydrolysis. A.R. Ling and J.L. Baker, as well as Brown and Morris, in 1895, proved that this isomaltose was not a homogeneous substance, and evidence tending to the same conclusion was subsequently brought forward by continental workers. Ling and Baker, in 1897, isolated the following compounds from the products of starch hydrolysis—maltodextrin-α, C36H62O31, and maltodextrin-β, C24H42O21 (previously named by Prior, achroodextrin III.). They also separated a substance, C12H22O11, isomeric with maltose, which had, however, the characteristics of a dextrin. This is probably identical with the so-called dextrinose isolated by V. Syniewski in 1902, which yields a phenylosazone melting at 82-83° C. It has been proved by H. Ost that the so-called isomaltose of Lintner is a mixture of maltose and another substance, maltodextrin, isomeric with Ling and Baker's maltodextrin-β.
The theory of Brown and Morris of the degradation of starch, although based on experimental evidence of some weight, is by no means universally accepted. Nevertheless it is of considerable interest, as it offers a rational and consistent explanation of the phenomena known to accompany the transformation of starch by diastase, and even if not strictly correct it has, at any rate, proved itself to be a practical working hypothesis, by which the mashing and fermenting operations may be regulated and controlled. According to Brown and Morris, the starch molecule consists of five amylin groups, each of which corresponds to the molecular formula (C12H20O10)20. Four of these amylin radicles are grouped centrally round the fifth, thus:—
By the action of diastase, this complex molecule is split up, undergoing hydrolysis into four groups of amyloins, the fifth or central group remaining unchanged (and under brewing conditions unchangeable), forming the substance known as stable dextrin. When diastase acts on starch-paste, hydrolysis proceeds as far as the reaction represented by the following equation:—
The amyloins are substances containing varying numbers of amylin (original starch or dextrin) groups in conjunction with a proportional number of maltose groups. They are not separable into maltose and dextrin by any of the ordinary means, but exhibit the properties of mixtures of these substances. As the process of hydrolysis proceeds, the amyloins become gradually poorer in amylin and relatively richer in maltose-groups. The final products of transformation, according to Brown and J.H. Millar, are maltose and glucose, which latter is derived from the hydrolysis of the stable dextrin. This theory may be applied in practical brewing in the following manner. If it is desired to obtain a beer of a stable character—that is to say, one containing a considerable proportion of high-type amyloins—it is necessary to restrict the action of the diastase in the mash-tun accordingly. On the other hand, for mild running ales, which are to "condition" rapidly, it is necessary to provide for the presence of sufficient maltodextrin of a low type. Investigation has shown that the type of maltodextrin can be regulated, not only in the mash-tun but also on the malt-kiln. A higher type is obtained by low kiln and high mashing temperatures than by high kiln and low mashing heats, and it is possible therefore to regulate, on scientific lines, not only the quality but also the type of amyloins which are suitable for a particular beer.
The chemistry of the nitrogenous constituents of malt is equally important with that of starch and its transformations. Without nitrogenous compounds of the proper type, vigorous fermentations are not possible. It may be remembered that yeast assimilates nitrogenous compounds in some of their simpler forms—amides and the like. One of the aims of the maltster is, therefore, to break down the protein substances present in barley to such a degree that the wort has a maximum nutritive value for the yeast. Further, it is necessary for the production of stable beer to eliminate a large proportion of nitrogenous matter, and this is only done by the yeast when the proteins are degraded. There is also some evidence that the presence of albumoses assists in producing the foaming properties of beer. It has now been established definitely, by the work of A. Fernbach, W. Windisch, F.Weiss and P. Schidrowitz, that finished malt contains at least two proteolytic enzymes (a peptic and a pancreatic enzyme).
The green beer is filled into the casks, and the excess of yeast, &c., then works out through the swan necks into the long common gutter shown.
The hot wort trickles over the outside of the series of pipes, and is cooled by the cold water which circulates in them. From the shallow collecting trays the cooled wort is conducted to the fermenting backs.
The presence of different types of phosphates in malt, and the important influence which, according to their nature, they exercise in the brewing process by way of the enzymes affected by them, have been made the subject of research mainly by Fernbach and A. Hubert, and by P.E. Petit and G. Labourasse. The number of enzymes which are now known to take part in the brewing process is very large. They may with utility be grouped as follows:—
|Name.||Rôle or Nature.|
|In the malt or mash-tun.||Cytase||Dissolves cell walls of of starch granules.|
|Diastase A||Liquefies starch|
|Diastase B||Saccharifies starch.|
|Proteolytic Enzymes||(1) Peptic.|
|In fermenting wort and yeast.||Invertase||Inverts cane sugar.|
|Glucase||Splits maltose into glucose.|
|Zymase||Splits sugar into alcohol and carbonic acid.|