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JOURNAL OF THE COLLEGE OF AGRICULTURE, IMPERIAL UNIVERSITY OF TOKYO
Vol. 5, No. 1, P81-94.
OCTORVER 24TH, TAISHO 1 (1912)

BY S. Muramatsu

There are several kinds of natto prepared in Japan, but here I mean common natto, which is a kind of vegetable cheese made by fermenting boiled soya beans wrapped in the straw and set in a warm cellar for one or two days.
Thus the product becomes white and mucilageous by the development of bacteria. Natto is consumed as a by-food after having been mixed with table salt and several stimulants, of which amongst others powdered mustard is preferred. It is chiefly consumed in Tokyo and the north-east districts of Japan, and for the production of it Aizu is the noted place. It is consumed in Tokyo in the summer time, but in the north-east districts during the winter time, as these are rather poor in vegetables at that season.

There exist several studies on Natto so far, as to its constituents and the micro-organisms growing on it, but no exact investigation is known about its preparation. So its manufacturers suffer under many difficulties in preparing natto of good quality; for this reason, I was induced to make a study of the method of preparing it and on several other points. Besides, I think it is very useful to prepare natto of good quality and increase its consumption by the people, as it is a very good and economical food stuff, being cheap and containing much protain; especially in our country, where rice is the principal food.

（中略： boiled soya beansの成分表を含む）

Rice straw is used for the wrapper of boiled soya beans. Fresh straw is preferable to old, as its smell is better than that of the latter. The straw is cleaned by taking the muddy leaf away from the under part of the stem and then washed with clean water; afterwards, it is well at its two ends, leaving several inches apart, and bundled after filling the bag with the beans. As to the reason of using straw for the preparation of natto, it was considered that the straw supplies the proper bacteria to the beans; but I do not think this the sole reason, for we can prepare it another way, as for instance, by setting it in a sterilized Petri-dish or in a basket.
When it is made in a basket, which after filling it with beans is out in a warm cellar covered with a straw mat, it is called basket-natto. From this and others facts it is reasonable to consider the principal objects of using straw for the preparation of natto to be:-

• 1.The supply of the good aroma of straw to natto.
• 2.To take away ammonia from natto.
• 3.To offer good ventilation of air to the loosely packed beans.

...（後略）

The cellar for the preparation of natto is made with bricks or with wooden piles surrounded thick layers of straw and the walls plastered with mud; the entrance is furnished with a thick door preventing the air to enter.
Along the inside of the wall a long shelf two feet wide is set up at the height of almost two feet and one or two large hearths are made on the floor for the purpose of warning the room.

For the preparation of natto the soya beans are sorted first and all beans that are broken or imperfectly developed are picked out.

After washing with clean water, they are soaked for several hours and boiled inn an iron kettle until they become moderately soft. (ca. 5 hours) The boiled beans are pit into the straw bundle while they are still hot, and the bundles are placed, standing obliquely, on the shelf in the cellar, which is previously warmed by charcoal to about 40ºC. The cellar is then shut up carefully, to avoid the circulation of air; thus, the beans become natto after one or two days and are ready for consumption.

As to the micro-organisms of natto several authors have made investigations.

Dr. YABE isolated three species of micrococci which formed yellow, orange, and white colonies respectively, and a bacillus which is nato motile, liquefying gelatine and producing a greenish fluorescence. He attributed the production of the characteristic aroma of natto to the development of the micrococcus which produces yellow colonies; but no explanation was given about the formation of the viscous substance.

Dr. SAWAMURA isolated various kinds of bacilli and micrococci from natto and regarded the following two bacilli as the chief microbes for the production of natto.
Bacillus No.1 is a motile and facultative aerobe.
Natto produced by this bacillus had a good taste and aroma, but its viscosity was natto so great as that produced by the other. The author gave the name of Bacillus Natto to this bacillus, considering it as the chief microbe in the fermentation.
Bacillus No.2 is a rarely motile and facultative aerobe.
Natto produced by this bacillus showed a stronger viscosity, but a less nice taste and aroma than that produced by the B. natto; he recognised it as a variety of Bac. mes. vulgatus. Thus, he concluded that for the formation of good natto both bacilli　must be present.

Mr. MONZEN isolated several kinds of bacteria, among them one bacillus to which Dr. OMORI gave the name of Bacillus viscosus natto and which, he said, is the principal microbe that produces strong viscosity The two kinds of bacilli which he named Bacillus odorans natto 1. and Bacillus odorans natto 2, produce good aroma in natto; and another one which he named Pseudomonas odorans natto, produces also good aroma. The latter three did not produce good natto, unless the material is inoculated also with B. viscosus natto. Thus the author concluded that there are necessary for the preparation of natto at least two kinds of bacteria, one producing the peculiar aroma and the other strong viscosity.

Mr. MUTO isolated several bacteria and concludes that only one bacillus belonging to the B. subtilis group is necessary for the production of natto.

I investigated also several kinds of natto, prepared in Tokyo, Aizu, and Morioka, and found that they all contain the same micro-organisms, amongst which the following three bacilli are principal ones. Several other bacilli are not suitable for the preparation of natto, as they produce bad colour or smell, and make the natto unfit for eating.

Two micrococci were found, one of which was analogous to Mic.flavus, and the other producing a translucent colony on agar plate-culture: but, both these micrococci having no relation to the preparation of natto, I gave up their further investigation.

This bacillus develops most energetically at high temperature(40-50ºC.) and produces the best quality of natto, providing much mucilage and good aroma.
...（中略）
This bacillus may be the same as those which Dr. SAWAMURA represented Bacillus No. 2 and Bacillus viscosus Omori, and also that which Mr. Muto thought was the only bacterium which produces natto, though they are several differences in this behaviour investigated by these authors.

This bacillus develops most energetically at high temperature and produces the best quality, forming much mucilage and rather higher aroma than Bacillus No. 1.
...（中略）
Concerning the behaviour against heat and several compounds as formerly mentioned, there is not much difference with bacillus No. 1. This bacillus may be the same as that which Dr. SWAMURA named Bacillus natto, though there are several difference in its behaviour. As this bacillus does not produce any mucilage at low temperature (say 35ºC) he thought it, perhaps, to be one which produces aroma peculiar to natto; but, as I mentioned already, this bacillus produces much mucilage at higher temperature and makes good natto with high aroma.

This bacillus develops most energetically at 40ºC, and when it is developed on boiled soya beans at this temperature, it produces good natto with strong viscosity and good aroma; but its mucilage is somewhat less than Bacillus No. 1 and Bacillus No. 2.
...（中略）
The behaviour to head and several compounds is almost the same as with Bacillus No. 1, although there are some differences. This may be the same bacillus as Bacillus grossus, but as there is no detailed description of it, I cannot make precise comparison.

As mentioned already, when we prepare natto in a glass dish at ca. 38ºC. inoculated with bacillus No. 1 it has some viscosity, while others have not, but the aroma was inferior to that made in straw bundles, for it does not touch straw. At 45ºC. all bacilli produces natto of fine quality, providing strong viscosity and good aroma; the aroma produced by Bacillus No. 1 was the best, while Bacillus No.2 produces a rather strong smell of ammonia, and that of bacillus No.3 was the worst. Moreover, I prepared natto according to the common way differing only one of the point of inoculating these bacilli separately and also mixing them with one another.
The result was that natto which was produced by the inoculation of Bacillus No. 1 was the best, as it has much mucilage and fine aroma, while Bacillus No. 2 produced an inferior and Bacillus No. 3 the worst quality. Natto produced by the inoculation of mixed bacilli was nato so good as that produced by each bacillus; so, there is no necessary that two or more bacilli be present for the formation of good natto.
By the inoculation of cultured bacteria we can entirely avoid failures and can prepare good natto by selecting the bacteria. Otherwise, it is sufficient to put it in the cellar for only one day, after which the natto will be ready for consumption. I recommend, therefore, the use of the pure culture of proper bacteria in the following way:

The bacteria developed on the slope culture medium of agar are mixed with juice produced by the boiling of beans.
This is poured over the surface of boiled beans while they are still in the kettle, the further processes being the same as usual.
There is no necessity of mixing several bacilli.

As natto is prepared from soya beans which are rich in protein and carbohydrates, it contains yet much protein and carbohydrates; the nutritive value of it is greater than that of boiled soy beans, for it is rich in soluble matters produced by the micro-organisms.

The composition of natto differs exceedingly with age, but its mean composition is as follows:(Compare with the composition of boiled soya beans.)
（成分表を略す）
The micro-organisms which grow on the soya beans secrete trypsin and diastase; so, when we take it together with several foods rich in protein or starch, they may be digested more rapidly than when they are taken alone.

I express many thanks to 'Dr. SATO, Director of our College', who helped me in determining the quality of natto that I prepared, and also to Mr. N. NITTA and Mr. Y. TANAKA, who assisted me in these investigations.

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近代納豆あれこれ
On Bacillus Natto BY Shin Sawamura; 東京帝国大学澤村博士の追試レポート
近代納豆文献リスト