cylinder is filled with boiling-hot sterilised wort from the brewery; it is then cooled, aërated through m and, after this has taken place, a part of it is passed over into the fermentation cylinder by means of air pressure. The pure cultivated yeast from the laboratory is then added, the stirring apparatus set in motion, and later on more wort is added. As soon as the proper amount of yeast is formed, the beer is drawn off, and the sedimentary yeast stirred up and mixed with the small quantity of beer remaining; this mixture is then taken out, to be used as pitching yeast for FIG. 52. The Construction of the FIG. 53. The Construction of the Lower tus. a small fermenting vessel (with about 8 hectolitres of wort). Wort is then added for the next culture. A detailed description and guide for the use of the pure yeast culture apparatus described here as well as of the pure culture system in general was given by E. Chr. Hansen himself in his Practical Studies in Fermentation, London, 1896. Exact directions are given which are the outcome of very comprehensive experiments, which he made in the Old and New Carlsberg Breweries, Copenhagen, as well as of extensive observations in these and other breweries at home and abroad. Some modifications have been made in the apparatus just described, which is the most extensively used form, and changes have been introduced by the following, among others: Bendixen, Bergh & Jörgensen, Brown & Morris, Elion, Lindner, Marx, Thausing and Wichmann. However carefully one may work there is always the possibility of infection taking place in the apparatus by some unfortunate means. It is therefore necessary to subject the yeast produced in the apparatus to a controlling analysis from time to time (see page 137). The yeast in the apparatus should not be changed without good reason. If the apparatus is manipulated carefully it will remain free from infection for years. As already stated, Hansen began his laboratory researches on pure culture yeast races in 1881, and carried out conclusive experiments in practice two years later in the Old Carlsberg Brewery. When the new reform had gained a firm foothold there and in several other bottom fermentation breweries, it naturally resulted in its extension to the other branches of the fermentation industry. The Pure Culture System in Top Fermentation Breweries. The first to experiment in practice with purely cultivated top yeast was Alfred Jörgensen, who, in 1885, introduced a yeast of this kind into a Danish top fermentation brewery with most satisfactory results. The method was the same as that described above, used by Hansen in bottom fermentation breweries, but in some cases it was found advisable to aërate the wort a little, as clarification proceeded somewhat slowly. Subsequently a large number of good species of beer top yeast were isolated by Jörgensen, Schönfeld and others, and the pure culture system introduced into numerous top fermentation breweries on the continent, although not to such an extent as in bottom fermentation breweries. Modifications of the Hansen-Kühle pure culture apparatus have been designed by Jensen, Jörgensen, Kokosinski and Wilson for use in top fermentation breweries. The Pure Culture System in Wine Manufacture. The Hansen pure culture system has attained great importance in the preparation of wine. The systematic selection from the numerous wine yeast races is here probably of even greater significance than in the other branches of the fermentation industry. In this case the most varied demands are made on the yeast, which are probably directed for the most part to obtaining a better product from inferior material. In this domain also pure yeast has realised completely all reasonable expectations, although it cannot be denied that many expectations went beyond reasonable limits. The first to use Hansen's system in wine manufacture was one of his pupils, L. Marx (1888); later on, Hotter, Mach, Müller-Thurgau, Portele, Seifert and especially J. Wortmann have extended the application of the system in this sphere. The technique of pure culture in wine manufacture is somewhat different from that in the other branches of the fermentation industry. In a brewery, a sterilised liquid is dealt with, a wort; but it is not possible to sterilise must, as it would take up the so-called boiled flavour and the wine would thereby depreciate in quality. This circumstance entirely prevents the use of sterilised must in the preparation of wine. The germs present in must are, however, as a rule so weakened that they only develop after some time; a large quantity of a vigorous young growth of the selected pure yeast is therefore added at once to the must, and foreign germs are by this means suppressed. This action is assisted very considerably by the chemical composition of the must; and it is this also which is responsible for the fact that spontaneous fermentation has been advantageously employed for so long a time, a good product being obtained without sterilisation or centrifugalising. According to Wortmann's researches the end products of fermentation, as well as the quantity of these, are the same, whether little or much yeast be added; but the more yeast added to the must, the quicker is the fermentation. It is best when fermentation proceeds quickly, as, in consequence, the foreign germs present in the must are more completely suppressed; the fermentation may, however, be too violent if an excessive quantity of yeast is added; the result of this is, that the must not only froths over easily and a part of it is thus lost, but, by the vigorous production of carbonic acid, bouquet substances are also carried off at the same time and the wine loses in quality. With regard to the quantity of yeast to be employed, the following numbers given by Wortmann may serve as a guide: With light musts, i.e., musts containing about 18 to 20 per cent. of sugar, one can rely with certainty on the fermentation being controlled by the pure culture yeast and consequently on a good result if fromto per cent. of yeast is added. By this is understood that to every 100 litres of fresh must is added to litre of a must brought into vigorous fermentation by means of a pure yeast. Good results are also obtained with the larger addition of to 1 per cent. But Wortmann found the effect of still larger additions of yeast to be too great with light musts. With heavy musts the addition of yeasts may be much larger, i.e., up to 1 per cent. or even more, without fear of bad results. If it is desired to re-ferment wines not thoroughly fermented, or sugared wines, the addition of pure yeast should be still greater, in fact 2 per cent. or The same holds good for the employment of pure yeast in the preparation of sparkling wine. If wines which have stopped fermenting are to be forced with pure yeast, over. Wortmann recommends a yet greater addition of yeast, up to 10 per cent., according to circumstances. The temperature of the fermenting room requires careful watching; it should be kept lower than it is otherwise usual to keep it, so that in fermentations to be carried out on the large scale with pure yeast, the fermenting may not be too violent. It is, in addition, important to employ the yeast at the proper stage of development. The yeast must be in such a condition that, when placed in the must, it can immediately continue its development, so as to obtain the mastery in as short a time as possible. Therefore the practitioner obtains from the laboratory small quantities of yeast, which he then increases in definite quantities of must. Since the number of wine yeast races brought into use is large, and the fermentation of grape must is limited to a few weeks in each year, a pure culture apparatus such as that which has been described for use in brewing for the continual production of yeast in mass is not applicable in this branch of work. Laboratories would require to have a large number of such pure culture apparatus, and even if they possessed them it would be impossible in the short time at disposal to produce the quantity of yeast necessary for the work. Consequently stations and laboratories dispose of the pure culture yeast in small quantities which the practitioner then increases for himself. In cultivating the yeast, laboratories employ sometimes the concentrated must mentioned on page 80 and sometimes a must pressed from home-grown grapes; the former is diluted with water. In cases where a specially vigorous yeast is required, e.g., in re-fermentations and fermentations of unfinished wines, the employment of well-nourished, non-aërated yeast is to be recommended. Pure yeast is supplied to wine producers in a thin |