Monday, May 27, 2013

Batch # 40: Back on track

After the last batch which turned out okay, I made a really good batch of natto. Mainly it is due to the new frozen natto pack that I used to ferment this batch. I did note the brand: Shukuba Nattou by Murakami. I bought it a few weeks ago probably because it was on sale.

Batch #40 looked slightly wet but had good sticking power. With shoyu, it formed thick long threads.

The freshly made natto almost had a pleasant apricot smell

One thing I like about making natto in the summer is that the fermentation seems to go smoother. I have come to associate this with temperature. This is especially true when I was making natto with only a yutanpo as the heat source. I have not seen many homemade natto makers mention this, but natto fermentation is truly a metabolic marvel. Each individual natto bacteria is going about its life eating and multiplying. This in itself is an insignificant event that is too small in scale to matter but in large numbers, it takes a whole new dimension.

I mention this in relation to natto making in the summer time because I have noticed that when the ambient temperature is high enough, the natto fermentation can continue with its own generated heat. I did not notice this at the beginning and was baffled why the natto fermentations in the summer seemed to go better than the winter fermemtations when using a yutanpo. After a while, I bought a thermometer to keep track of the fermentation temperature and I discovered something truly amazing. Seven hours into the fermentation to somewhere around the fifteenth hour of fermentation, the natto superorganism consisting of billions of individual natto bacteria metabolize the food in soybeans and generate enough heat to keep it at its ideal growth temperature without requiring an external heat source. This is evident when making large quantities of natto, in my case 400 grams of dry soybeans (~1 lb), when the ambient temperature is somewhere around 23C/75F or higher. The glass baking dish which has insulating qualities in addition to the double cling wrap to cover the top helps to retain the heat.

So in essence, it is possible to make natto if it is possible to maintain an ideal temperature in the first 6 hours of the fermentation using a low tech, cheap method such as warming the oven for a few seconds every hour or by using a yutanpo. Using a small cooler or styrofoam box, which I have not tried, would probably suffice to make good natto if ideal temperatures can be kept for the first 6 hours until the natto kick in to generate its own heat. After the natto slows down, the natto could be kept in the cooler for another few hours to let it ferment with the latent heat.


  1. Hi, I have tried your method yesterday, and for the first time, my natto was edible, but the string was not that strong. I used thawed natto, do you think it matters? I will try different brands as you say. (well, I did not leave it on the counter for 24hrs...)

    I have tried making natto in a cooler box with a plastic bottle filled with hot water inside. Maybe the dish were not sanitized well. Ammonia smell was very strong.

    Interesting findings about the temperature. When I made it yesterday, I turned the oven on for 10min at warm setting(170F), and placed the natto inside.( I do this when my homemade yogurt does not come out right) Then, I did the same thing after 4 hours or so with natto left inside before hitting the bed.

    I'm gonna keep trying to make a successful batch like yours, but thanks a lot for my first edible batch!

    1. Thank you your comment! Took me a while to figure out how to reply to a comment :b... Anyways, I am happy that you made your first edible natto! My first 30+ batches were barely edible with tons of ammonia.

      Not knowing how you make natto, it is hard to say what's up. So if you haven't done so already please check the troubleshooting guide on the Natto Dad blog. If your soybeans are well steamed to the point that they are soft, dark beige and almost creamy, my next thought is to check the temperature and packaged natto.

      To answer your question, I don't think it matters that you use thawed packaged natto. You can go ahead and use a frozen cube also. As for contamination, this is not a primary concern, if you pour boiling water in the dish or use a mild solution of chlorine (rinse before use)to sanitize.

      As for the temperature, if you warm the oven for 10 mins, make sure that the oven is not too hot when you put it in. I would wait until it cools down a little. If possible, experiment by putting a desk lamp, yutanpo, or pot with hot water to keep the temperature higher for longer. If you can successfully maintain a temperature as close to 40C (~100F) for the first 7 hours, the natto will have a good starting fermentation. The other 10-12 hours, you can relax a little and check the temperature one or twice.

      Keep experimenting and let me know how it goes! I make natto every week, and I was thinking of writing a "Back to basics, low tech methods of making natto" post. So I am collecting info on what methods work and what definitely does not work.

      Happy natto making!

    2. Thanks for this wonderful info.

  2. Hi Selena! Thank you for your input. I checked the cooler out and it is very hip looking. You are making natto in style. Do you leave the cooler slightly cracked open to let air in? Or does it have some slight air gaps? I was wondering if natto will ferment if sealed air tight.