Table 8: Composition of Koji Dried at 100° C.
Dextrose
9.84
1.50
8.23
1.83
Insoluble Albumenoids
Koji is prepared both in breweries and in special works, as it is used for various purposes besides sake making. It will be most convenient for us to examine the mode of manufacture in the special koji works, as there will be found the conditions essential to its successful production more readily than in the sake breweries. I am especially indebted to Mr. Jihei Kamayama of Yushima, Tokyo, for much information as well as for permission to investigate at his works the whole process of manufacture.
The essential part of the process is carried out in long narrow passages cut in the solid clay about 15 or 20 feet below the surface of the ground. The object o f this is to have a chamber which being once heated will not easily lose its hea t either by radiation or by conduction. That this result is produced by cutting the chambers in the clay is shown by the constancy of temperature which they are found to possess even when considerable changes take place in the temperature o f the outer air. Clay is a very bad conductor of heat, and it is practically imp ossible for heat to be communicated either to or from these passages through the clay. The passages are about 25 or 30 feet in length, and each set is reached t hrough a very low and narrow one---made so for the purpose of preventing as much as possible an exchange between the outer and inner air. The opening passage is not more than between 3 and 4 feet high and about 4 feet wide, and is usually c losed with mats. It is approached by descending a shaft from the ground above, a nd at the other end it opens into a passage of somewhat larger dimensions, from which two others branch off nearly at right angles. It is in these innermost par ts that the highest temperature is maintained. In the sake-breweries the warm ch ambers are less carefully constructed, being built near the surface of the groun d of wooden planks coated with mud and thickly covered over with straw mats. Thi s is evidently a less perfect method of keeping in the heat than that adopted in the koji works proper. Having described the apparatus used we may now consider how the rice is treated. It is brought to the works husked but not cleaned, and the process of cleaning or whitening, is done by the manufacturers. This consists in removing that thin outer skin, the testa, which, as we have seen, contains a large proportion of cellulose and mineral matter. It is removed by the brewers, as they say, because it would render the liquid brewed very liable to putrefy. In removing the bran the rice suffers a considerable loss of weight, owing not only to the loss of the testa, but also to the fact that many of the grains become broken and are rejected on that account. In most places the cleaning is effected by human labor. The rice to be cleaned is placed in a wooden mortar sunk in the ground, and a heavy wooden hammer supported upon a fulcrum is so arranged that on pressing down the side of the lever away from the mortar and then removing the pressure, the heavy end of the lever falls by its own weight into the mortar. As it falls it causes the grains of rice to rub against one another and so the skin becomes scraped off. The loss of weight varies according to the degree to which the cleaning is carried; that which is used for the preparation of koji and of moto (called moto-mi) loses from 30 to 40 percent of its volume, whilst the kake-mi, used in the stages designated soye, naka, and shimai, is not so thoroughly cleaned and loses only about 25 percent of its volume. The numbers given are, of course, only approximate for, in every operation the percentage of loss must be different. The pounded mass is separated into three portions---the whole grains---the broken grains, and the bran. The whole grains are employed in the manufacture of koji and sake, the broken grains are sometimes made into an inferior kind of koji, but generally, like the bran, are sold to other persons. The amount of bran obtained is said to be about 3 kuwamme (25 pounds) for every koku (4.96 bushels) of rice cleaned.
In some works (sake-works) steam power is employed to work the cleaners, and in other places water power is used.
The rice is next placed in a tank, covered with water, and from time to time tro dden upon by the workmen, the water being frequently changed. The fine dust whic h was adherent to the grain is carried away by the water, but the amount of matt er thus lost, although sufficient to make the water milky is not known. After this washing the grains is left in steep for one night by which it becomes quite soft and is ready for steaming. The object of the steeping is merely to render the grain soft so that the subsequent steaming may be as short as possible. It is therefore, not analogous to the steeping of the barley-grain in making malt, an operation which is required to promote the germination of the embryo. In the case under consideration, indeed, the embryo has been completely destroyed by the rough beating, and no subsequent germination is possible. It is important to remember this, so that it may be clearly understood in what respects the manufacture of koji differs from that of malt. But even were the embryo not removed by the process of cleaning, it would be completely killed by the next operation, that of steaming. The soaked rice is placed in a large tub which is provided with a false bottom covered with cloth; the tub is then fixed upon an iron boiler full of water. When the water boils the steam passes through an opening in the true bottom of the tub, and as it ascends through the rice which is placed upon the cloth covering the fast bottom, it heats the grain and causes the starch to become gelatinized. The grains of steamed-rice are flexible and of a horny appearance, and must be the same throughout. In this state the rice is called mi. It is now spread out upon mats to cool, and during this time the workmen prevent the grains cohering by rubbing them between their hands. When the temperature has fallen to about 29°C the foreman mixes with the rice a small quantity of tane, a yellowish powder consisting of the spores of a fungus described by the late Mr. Ahlburg under the name of Eurotium oryzeae (Ahlb).1 The quantity employed is not exactly the same in different works, but averages about 3cc to 4 to (72 liters) of rice.
The subsequent operations vary a little in different works but not in any essential particulars. I shall, therefore, only describe them as carried out in the koji works at Yushima, Tokyo.
Until 1 p.m. in every case the temperature of the koji is above 100° F., and after 1 p.m. in every case it falls below that point. The period of most active growth is, therefore, in the morning, and corresponds with the time during which the material is heaped up in masses. The effect of opening out the masses of koji will be best seen in the temperatures taken on Dec. 6th. At 8 a.m. the temperature was 106.6° F. and it continued to rise a little until between 9 a.m. and 10 a.m. when the workman broke open the heaps and spread them out. The temperature taken at 10 a.m. shows that the mass had cooled down 5.6° F. After this the mixture was again made up into heaps and at 1 p.m. the temperature had again rise, though not quite so high as at 8 a.m. After the heaps have been broken down between 1 p.m. and 2 p.m. the rice continues to cool; on the 5th the temperature at 2 p.m. was 91.9° and at 8 p.m. had fallen to 88.8°F. The object, therefore, of the working of the mass is not so much to prevent the grains becoming too much matted together as to regulate the activity of the growth of the plant. If the grains were allowed to remain heaped up during the whole time, there would be a danger of the temperature rising to too high a point, and perhaps rendering the product useless, whilst if the grains were never collected into heaps, the temperature would not rise sufficiently high to allow the growth to go on vigorously.
Comparing these with the analyses of whitened rice given on page 10 it will be observed that the amount of starch present is much reduced. This is due to its conversion into dextrose and dextrin, which has been mainly effected during the solution in water, owing to an active agent contained in the koji of which more will be said hereafter. The percentage of starch which would correspond to the dextrose, dextrin. and starch given in the first analysis is 82.4%, a number very closely agreeing with that which the rice dried at 100° C actually contained. The actual loss of material during the growth of the fungus cannot be determined, therefore, by an analysis of the koji, although the increase in the total amount of albumenoids indicates that there has been a loss of some of the other constituents of the grain. The large proportion of soluble albumenoids will strike every one, but as this is connected with the existence of a kind of "diastase" contained in the koji, it will be referred to in connection with the properties of that body.
The loss of material caused by the growth of the fungus is evident when we consi
der the weight of koji formed from a given weight of rice. Mr. Jihei Kamayama wa
s kind enough to make careful weighings of the rice used and of the resulting ko
ji. The result obtained was that 3 to of whitened rice which weighed 11.43 kuwam
me yielded 12.38 kuwamme of koji, or 100 parts by weight of the rice gave 108.3 parts by weight of koji. The rice contained 14.2% of water, and the koji contained 29.5%, therefore, deducting the water from each, we find that 85.8 parts of dry rice gave 76.4 parts of dry koji, equal to 89%, or in other words, 11% of material was lost by the dry rice. This loss is probably nearly all starch, and if so, every 100 parts of rice converted into koji would evolve nearly 18 parts of carbonic acid. Now 107 pounds of dry rice are converted into koji every day in each chamber, and thus evolve 19.2 pounds of carbonic acid measuring 2240 liters. The total capacity of each chamber cannot be more than 20,000 liters, and therefore in order to remove the carbonic acid formed a constant circulation of air is necessary. If this were not provided for the air would not only become irrespirable by the workmen, but would also become unfit for the growth of the plant which requires a supply of oxygen. At the same time care has to be taken that the current of fresh air is not sufficiently rapid to lower the temperature of the air within the chamber. The mode of ventilation depends upon the difference in temperature between the inner and the outer air, the inner air being warmer rises up a square shaft at the front end of the series of passages, whilst the cold air bringing fresh oxygen enters and flows along the floors of the chambers, until in its turn it is warmed and rises through the shaft to the air above. This method is amply sufficient during winter when the difference of temperature between the air outside and inside is about 40°F, but when, as in the spring and early summer the difference becomes less than 10°F, frequent stoppages occur. This, perhaps, might be remedied by burning a small fire at the foot of the shaft, and thus artificially causing a draft, but as a smaller quantity of koji is required in summer, it is not of so much importance.
2 Journal Chem. Soc. 1880 Trans. p. 650.
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