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light of onr modern knowledge of starch conversion, determinations of the optical properties and the cupric reduction of a wort or of a beer, and of the behaviour of the same towards malt extract and yeast, &c., constitute valuable subsidiary methods for controlling and regulating the brewing operations. Several amyloins of definite composition have been isolated, one being amylo-dextrin (C12H20O10)6 (C12H22Ou), and another malto - dextrin (C12H20O10)2 (Ci2H22On). The first is an amyloin of a “high,” the second an amyloin of a “low ” type. The amyloins are not split up in the primary fermentation, but are converted into maltose more or less rapidly, according to their type, during the secondary fermentation. 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-tub accordingly. On the other hand, for mild running ales, which are to “condition” rapidly, it is necessary to provide for the presence of sufficient malto-dextrin of a low type. Investigation has shown that the type of malto-dextrin can be regulated not only in the mash-tub, 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 therefore possible to regulate on scientific lines, not only the quantity, but also the type of amyloins which are suitable for a particular beer. Cooling.—The introduction of refrigerators led many brewers to believe that it would be possible to do without the cooler altogether, but experience has shown that this was a fallacious conclusion. It is true that the exposure of hot wort on the cooler is attended with many dangers; but it is now known—thanks chiefly to Pasteur—that the oxygen necessary for the conversion of the hop-resins and other substances into insoluble modifications—that is to say, the chemically bound oxygen—can only be absorbed at a relatively high temperature. Beers which have not undergone a thorough hot aeration are liable to be of an unsatisfactory character, owing to the incomplete or tardy precipitation of the hop-resin, &c., in cask. In order, on the other hand, to overcome the dangers attendant on hot aeration, the greatest care must be taken with regard to the purity of the air-supply in the cooling-rooms. With regard to the refrigerator, the wort flows over it in a thin stream, and is, if anything, more exposed to infection during this process than on the cooler. Enclosed refrigerators with a purified air-supply are now being introduced into some breweries, and there is little doubt that this principle will in time be applied to the cooler also. Fermentation.—The study of the phenomena connected with the process of fermentation, and more particularly of those associated with brewing, has led to discoveries of epoch-making importance, both from a theoretical and practical point of view. Up till 1897 Pasteur’s theory of fermentation, according to which this process is indissolubly connected with the living cell, and the products of the fermentation of a saccharine liquid are actual products of yeast metabolism, was almost universally accepted as correct, the evidence in its favour being apparently overwhelming. The discovery in 1897 by Buchner that it is possible to obtain from brewing yeast an unorganized substance, which rapidly converts sugar into alcohol, carbonic acid, &c., outside of and quite apart from the living cell, has necessarily led to some modification of our views. According to Buchner, the substance in question is an enzyme to which he gave the name zymase. It may be obtained by grinding up yeast with quartz sand, then subjecting the mass of disintegrated yeast cells so obtained to great pressure, and finally passing the resultant liquid through a filter of the porous porcelain type. By evaporating this liquid at a low temperature the zymase can be obtained in the solid state, and may be kept for a considerable time without losing its property of causing fermentation. The cause of the activity of the yeast-cell juice has given rise to considerable controversy, and it is contended by some (Ahrens, Macfadyen and Morris, &c.) that it is not due to an enzyme but to particles of living protoplasm. So far, however, the balance of evidence appears to be in favour of Buchner’s enzyme theory, and

the fact remains that fermentation can be produced without the presence of yeast cells. The brilliant researches of the Danish chemist and botanist Hansen, which we will next consider, not only mark a new' era in our knowledge of the yeasts, but have probably had a greater influence on the rfermentation—and especially the brewing—industries than the w ork of any other man, excepting, no doubt, that of Pasteur. Hansen recognized the fact that it was impossible to study the life action and functions of micro-organisms, more particularly of the yeasts, without first obtaining these in a pure— that is, an unmixed or uncontaminated—state. The ‘ ‘ pure culture ” yeast of Pasteur [see under “Fermentation,” vol. ix. ninth edition) was not a pure culture in the true sense, as no certainty existed that the yeast obtained by Pasteur’s method did not contain more than one type of organism. Hansen perceived that in order to obtain a really pure culture—that is to say, a culture containing only one particular variety—it was necessary to start from a single cell. He successfully attained this object by two methods—first, by the dilution method, so called because a drop of liquid, the approximate number of organisms in which is knowm, is diluted to such an extent that the average drop of the dilute liquid contains less than one cell; and secondly, by a modification of Koch’s plate method, by which each cell, after the distribution of a small number amongst a suitable medium, is kept under microscopic observation during the whole of its development into a colony. By examining ordinary brewing yeast by these methods Hansen discovered that it consists of a number of different species and varieties, some of which are not favourable to the formation of a good beer, and it was found that not only bacteria and the socalled “disease-ferments ” (Pasteur, &c.), but also certain types of yeast proper possess various undesirable properties from the brewnr’s point of view. Hansen showed that although different species and varieties of the same species may appear identical under the microscope, they may possess properties of a widely divergent nature, and that by virtue of those properties they may be differentiated. The chief types occurring in ordinary brewing yeast are—(1) The various varieties of Saccharomyces cerevisioe ; (2) Sacch. Pastor I., II., and III. ; and (3) Sacch. ellipsoideus I., II., and III. Of these the S. cerevisice varieties are the true brewing yeasts. S. Pastor I. gives a bitter taste to the beer; S. Pastor III. and S. ellips. I. produce no particular ill effects, but are not characteristic beer yeasts ; the latter being in fact the most common species among the grape yeasts. Application of Hansen's Discoveries to Brewing. — In 1883 Hansen described a method by which he overcame a persistent tendency of the beers brewed at the Tuborg brewery near Copenhagen to become turbid. This he effected by introducing a pure yeast grown from a single cell. At the same time the Old Carlsberg brewery was afflicted in that its beer displayed a disagreeably bitter taste. Hansen examined the yeast in use there and discovered that it consisted of four varieties, and by experiment he found that only one of these gave a satisfactory beer; a pure culture of this was then tried in the brewery with excellent results, and has been in use there ever since. This is the yeast which is now known as Carlsberg bottom-yeast I. The advantages attendant on the use of pure yeast consist in the fact that it is possible to select the yeast which is best suited to the character of the beer which it is desired to brew, and that by always working with the same yeast it is possible to be absolutely certain of the results—that is to say, flavour, attenuation, stability, and so on, will remain constant. In Denmark, Norway, and Sweden the practice of brewing with pure yeast is wellnigh universal; it has also been adopted in most of the chief breweries in Germany and Holland, and in many cases in America. Hansen’s method has not yet made much headway in England, but it seems probable that in the course of time it will find favour there, but no doubt in a somewhat modified form. The chief difficulty so far is that the conditions under which English beer is fermented are quite unlike those obtaining for beer brewed on decoction lines, and also the radically different characters of the two classes of beer. In the English top-fermentation system the wort is pitched and fermented at a relatively high temperature —55°-65° F., sometimes higher. The fermenting vessels , are of enormous size, and therefore present a large surface