bacillus subtilis, transfer and culture

Natto is the Japanese name for a foodstuff prepared by treating cooked soy beans with bacillus subtilis 'natto' resulting in a strong smelling, slimy conglomeration of colonized beans. Although best known by the Japanese name, this is a traditional preparation that is widespread across Asia as, for example Kinema in N.E. India, Bekang in Mizoram, Thua Nao in Thailand and no doubt others. Traditional preparation using leaves and straw as innoculant likely introduces other microrganisms which would mediate the finished product somewhat. That's me speculating, I expect that the situation mirrors tempeh production and shares a disparity between traditional preparations and mass produced convenience items. Traditional tempeh with it's broader spectrum of innoculants for example is felt by some to have nutritional benefits that the pure culture item lacks. Mass manufacturing probably favours pure cultures for convenience and a consistent product.

The dish and the accompanying bacillus subtilis 'natto' enjoy a fair bit of attention. Seemingly real nutritional benefits (my reading) as well as interest in the physical properties of the stringy material that the bacillus produces.

After hearing someone mention that they'd just tried natto I decided to pick up a packet from the store and using that as an innoculant getting my own culture going. Web searches confirmed that this is feasible and offered guidelines and howto guides.



In a nutshell: soy beans were soaked in water overnight, then manipulated under running water to remove hulls. De-hulling was my own initiative; I've seen it in other bean processing and decided to do it here, not being too strict, but removing the lion's share of the hulls. Beans were drained and placed in a colander inside a pressure cooker to be steamed. The colander isn't submerged. Boiling is likely an option too. If you steam in a pressure cooker, perhaps line the base of your cooker as liquid from the beans scorched on the cooker bottom and required scouring. I think that I cooked for around an hour at 15 psi. When the beans were still warm from cooking a 50g container of store bought natto was mixed in very hot water and the resulting slurry mixed in to the cooked beans in a casserole dish. The dish was covered with aluminum foil which was perforated to allow air. The casserole dish was placed atop a pair of empty jars in an insulated picnic hamper thingy to incubate. Heat was provided by water in the base of the hamper and an aquarium heater. The incubater was left at about 35C for 24hrs, at which point the beans appeared well colonized, a filmy covering in evidence. The same smell from the original packet is well established as well as perhaps a hint of ammonia. I'm speculating, and will verify, that stronger smelling preparations can be had with more time.


conversation piece

As an exercise I decided to attempt isolate the culture on agar with otc media. I soaked overnight and then boiled for an hour and a half a handful of beans to acquire liquid for agar medium. As the beans were still relatively intact I used the back of a spoon to crush them enough to obtain a rich looking broth. I added agar from the grocery store to the broth and sanitized in the pressure cooker for 30mins. I poured several plates and from a friend's recommendation let them sit undisturbed in a draft free enclosure for 48hrs so as to dry off the media surface. I made a wire loop from ... wire, and catching strands from separated beans I innoculated ths plates. The plates were left at room temperature for a few hours and then incubated for about 16hrs at 35C.



My conclusions. Transferring natto from store bought items is a lead pipe cinch. Materials are cheap, incubation time is fast. Web searches show that bacillus subtilis is quite robust and a popular choice for those investigating microbial affairs. The agar culture that I did might benefit from some research into SOP, and the incubater whilst seeming ok for the beans was too humid for the plates I think. The food item is a good conversation piece, and typing reports is time consuming and easier to just imagine doing.




crude composition of media shows through

Quote: Originally posted by bbartlog

Nicely done! Natto always sounded kinda repulsive to me, but the experiment is cool regardless.

Thanks. I think that a lot of people would be squeamish about eating these beans. I ate mine, but being able to gross out family and friends was an added bonus.

Nice work! I tried to try natto in Japan once. When I poked the beans and the white slime oozed out (non-newtonian fluids!) I jumped back in my seat and decided they were not for me. My brother did try them, but did not manage to swallow them

Quote: Originally posted by food

Thanks. I think that a lot of people would be squeamish about eating these beans. I ate mine, but being able to gross out family and friends was an added bonus.

Quote: Originally posted by watson.fawkes

The bad natto had little roundness to the flavor and a pronounced ammoniacal tang. It was also the cheap stuff, part of salaryman lunch at an institutional cafeteria in Tokyo. I'm guessing that higher incubation temperatures (for faster production) and machine processing of the beans had something to do with it, but I don't know the details. Good natto, on the other hand, is reminiscent of mold-ripened blue cheeses like gorgonzola. If you figure out what ingredients or techniques give this result, please do tell.