CHAPTER XLV. THE USE OF MUCOREÆ IN THE SPIRIT INDUSTRY. § 240.-Mucor Rouxii and other species of THE faculty of producing diastatic enzymes and thereby exerting a saccharifying action on both starch and dextrin, is possessed by a considerable number of the Mucors. For the earliest information on this point we are indebted to U. GAYON and E. DUBOurg (II.), who observed this faculty in Mucor circinelloides in 1886, and also found that this organism was only capable of exerting the influence specified when it developed in aggregations of gemmæ, but not when in the form of its normal mycelium. Shortly afterwards they reported (III.) on further similar experiments with Mucor alternans, and demonstrated that, under equal conditions, this organism converts starch into maltose and not into a hexose. The faculty is lacking in other species, e.g. Mucor racemosus, which, according to FITZ (IX.) also leaves inulin unacted upon. There are other more powerful species of Mucors, which, on account of their practical importance for the spirit industry, will now be fully described. For the preparation of rice spirit there is produced in China, Cochin China, and the neighbouring countries, an article known as Chinese Yeast, and put on the market in the form of flat mealy balls, about the size of a half-crown. Its preparation, composition, and application were first described in 1892 by E. CALMETTE (I.), whose reports were extended and supplemented by C. EIJKMAN (II.) in 1894. According to these authorities this so-called yeast is prepared by mixing equal quantities of husked rice-steeped in cold water-or rice meal and water, and pulverised aromatic drugs. The number of the latter varies, in different recipes, up to 46, but always includes garlic and galanga root. The resulting stiff paste is divided into small cakes of the shape mentioned above. These are laid on mats, previously coated with a thin but close layer of moistened rice husks (paddy), or are covered over with a layer of rice straw, and are kept in the dark for two to three days, at an air temperature of about 30° C. The balls, which by this time smell like yeast and have become coated with a fine white velvety covering, are next dried, either by exposure to the sun, or (in rainy weather) by gentle fire heat, and are then packed into bags for sale to the distillers. In India and China these balls are employed in the following manner: about 1 parts by weight of the finely crushed or ground mass are sprinkled over 100 parts of husked rice, that has previously been softened by boiling in water and cooled down sufficiently by spreading it out on mats. The two are intimately mixed together, placed in earthenware pots holding about 4 galls. (20 litres), so as to half fill the same, and are left covered up. The starch gradually saccharifies, and the mass consequently becomes partly liquid. At the end of about three days the pots are filled up with river water, and the sweet liquid is left to undergo alcoholic fermentation, which sets in very soon. This stage lasts two days, and the mash is then distilled in leaden retorts heated by direct fire. Each 100 kilos. of rice furnish about 60 litres of spirits, containing about 36 per cent. of alcohol. The flora of Chinese yeast consists of bacteria, which, however, are of no moment; then yeast cells, which must be regarded as the exciting agents of the alcoholic fermentation; and certain Mucors, which effect the saccharification of the starch. Of the last-named organisms, which alone concern us here, Calmette isolated a species, which, in honour of his teacher and colleague, E. Roux, he named Amylomyces Rouxii. He did not, however, ascertain anything definite respecting the morphology of this fungus and its position in the botanical system; but it was afterwards recognised as a Mucor by Eijkman, and its name changed to Mucor amylomyces Rouxii. The first thoroughgoing investigations regarding the progress of development of this organism were published by C. WEHMER (XI.) in 1900, who at the same time proposed to shorten the name to Mucor Rouxii. According to this worker the sporangiophore-which is about I m.m. long and 7 to 14 μ broad-is generally branched, and in many cases is decidedly sympodial (see Fig. 118). According to the conditions of nutrition the sporangia are either upright or declinate, globular, glass-clear and yellowish when ripe, and attain up to 50 μ in diameter. When they fall into decay a considerable remainder of the smooth, colourless membrane is left as a collar on the sporangiophore. The columella (Fig. 119) is globular, slightly flattened, smooth, colourless, and measures 23 to 32 μ by 20 to 28 μ. The spores are colourless, glabrous, and generally elongated (5 to 2.8 μ), rarely globular, and completely fill the sporangium. It is worthy of mention that the failure. to form sporangia noticeable in many Phycomycetes is also observed here as a frequent occurrence, the sporangium, instead of ripening, either ceasing to develop more than half-way, or else germinating as a tube in place of forming spores. This phenomenon does not appear in cultures on rice, but most usually occurs in those on sugar-agar, thus affording here a new and beautiful example of the influence of the conditions of nutrition on development. The mycelium produces an abundance of gemmæ, of different sizes and shapes, either globular (from 10 to 10 μ in diameter) or oval. They are colourless, or pale yellow to light brown, and have a very thick, smooth, colourless membrane. It is solely in the form of these resting cells that the fungus appears in Chinese yeast, to which, as Calmette has shown, it gains access from the rice husks and rice straw. explains why, in many places, the manufacturers of Chinese yeast consider it indispensable to press a few moistened rice husks into each of the fresh, pasty yeast cakes. As soon as the до This Fig. 118.-Mucor Rouxii. Sympodial branched sporangiophore, from a 7-days old culture on sugar-agar. Magn. about 160. (After Wehmer.) Fig. 119.-Mucor Rouxii. Sporangium almost entirely empty. Part of the wall still hanging in large shreds on the sporangiophore. In front of the globular columella are still lying three spores. From a culture on rice. Magn. about 230. (After Wehmer.) gemmæ arrive in a suitable nutrient medium they put forth germinating tubes and develop into mycelia. Up to the present no zygospores or yeast-like budding cells have been observed in this fungus. When grown on solid media (steamed rice in particular) the mycelium gradually assumes a highly characteristic orange colour due to golden yellow drops (oil?) appearing in the cell, but only at room temperature, though not at 40° C. The optimum temperature for the development of the mycelium lies between 35° and 40° C. According to Calmette, a temperature of 75° C. kills the organism within half-an-hour, and 80° C. is fatal in 15 minutes. The same observer states that the diastatic enzyme produced by Mucor Rouxii exerts its most powerful effects at 35 to 38° C., and is destroyed on being warmed to 72° C. According to BOIDIN and ROLANTS (I.), the sugar thus formed from the starch is glucose. Like lævulose, saccharose, maltose, and lactose, this sugar serves as a source of carbon to the fungus, and is burnt off provided there is direct access of atmospheric oxygen to the mycelium. If, on the other hand, the latter is compelled to remain submerged in the nutrient substratum, the glucose is also converted into alcohol. A. SITNIKOFF and W. ROMMEL (I.) state that the same also occurs in presence of d-mannose, fructose, galactose, trehalose, maltose, dextrin, and a-methyl glucoside, but not in presence of raffinose, lactose, saccharose, melibiose, xylose, arabinose, rhamnose, tagatose, ẞ-methyl glucoside, inulin, &c. The inability of this fungus to produce invertin was recognised by J. SANGUINETTI (I.). This worker also performed a series of comparative experiments on the effective force and conditions of the diastatic enzymes produced by Mucor Rouxii, M. alternans, and Aspergillus oryzæ, and found that the last-named is weaker than the other two, so far as regards the saccharification of dextrin, the greatest power in this respect being exhibited by the second. The appearance of free acids in the cultures of Mucor Rouxii is also recorded by the same observer; Calmette supposes oxalic acid, Eijkman, on the contrary, lactic acid. The amount of acid may be so abundant as to kill the culture. The industrial utilisation of this fungus in Europe will be dealt with in the next paragraph but one. At present we will conclude with the remark that Boidin and Rolants' proposal to employ this fungus for converting into sugar, or alcohol, the dextrin left in the residues from distilleries operated on existing lines, would probably be too expensive outside the laboratory. B-Amylomyces and y-Amylomyces are the names of two species of Mucor which have recently found employment in the so-called amylo process (§ 242), instead of Mucor Rouxii (a-Amylomyces). Colette and Boidin found the B species on Japanese rice, the other (y-Amylomyces) on Tonkin rice; and we are indebted to A. SITNIKOFF and W. ROMMEL (I.) for fuller researches on their morphology and physiology. According to these workers, cultures of these two species on a nutrient solution containing glucose can be readily distinguished from those of Mucor Rouxii, by the circumstance that, whereas the latter develops as a weakly, barren mycelium almost entirely within the liquid, the ẞ and y species, on the other hand, also grow on the surface, forming well-developed aerial mycelia, which project above the level of the liquid a distance of as much as 3 c.m., and bring forth sporangia. The latter often develop in a special manner. Instead of the tip of the sporangiophore gradually enlarging to a sporangium, the swelling here constitutes merely a preliminary stage. It does not itself develop into a sporangium, but puts forth one or more threadlike processes which may then become crowned with sporangia (one each). This is illustrated in Figs. 120 and 121. In both species the ripe sporangia are black, and of slightly flattened globular form, the transverse diameter varying between 45 and 95 μ, whilst the longitudinal diameter is about 15 μ smaller. The spores are oval or elliptical, brown in colour, and attain the following dimensions, in the The globular swelling at the apex of the hypha produces in the one case two branches, each carrying a sporangium, in the other case five branches, three of them exhibiting each a single sporangium in different stages of development. Magn. about 120. (After Rommel's original drawing.) FIG. 121.-Sporangiation in y-Amylomyces. In the one example the knoblike swelling has put forth three branches, each with a sporangium; in the other, one of the branches is short and has no sporangium, the other two being long, declinate, and carrying sporangia. Magn. about 80. (After Rommel's original drawing.) dry state: ẞ-species, length about 9 μ, breadth about 5.7 μ; y-species, 7 and 4 μ respectively. The formation of gemmæ on the mycelia is of very frequent occurrence, especially when air is excluded. The behaviour of these two fungi towards |