Wednesday, April 15, 2015

Two Frozen Natto Starters Compared

  I have been using packaged frozen natto as the starter for a long time. I did this by saving a portion of the freshly made natto and freezing it. When this became low, I saved a portion again and successfully did it until the third generation when it suddenly became unstringy. This was probably due to contamination or due to prolonged freezing killing the natto. I will never know the reason and for many batches after that, I tried to use the third generation starter to see if I could change the fermentation conditions to make stringy natto again.

After a while, I got tired of eating unstringy natto and gave up using my third generation starter. This was hard to do as I initially thought that I would be able to keep a starter culture indefinitely. To start over, I went to the Japanese market and got 3 packaged natto. The first two that I tried were, Tokyo Natto and Okame Natto. I forget what the third was... So I fermemted two batches side by side to see how the natto would turn out.

On the left is Tokyo Natto. I randomly picked this so there is no logical reason for this choice. On the right, Okame natto. A widely distributed long seller that is one of the most common natto brands.

These packages are kept in the freezer at all times. When frozen, I cut them into 12 small frozen pieces per package. So a 3 pack will yield 36 frozen natto starter cubes. I plop a cube into the steamed soybeans and mix it in. For full instructions refer to the Homemade Natto Recipe.

Might be hard to see, but Tokyo natto is a little bit weak visible by the shinnier appearance and thinner natto growth on the bean. Also when the cling wrap was pulled, stringyness was not too visible. As for the Okame natto, the natto growth was much stronger and stringyness was seen when the cling wrap was pulled back.

This to me is the moment of truth when the natto is stirred with chopsticks. Here, the difference in natto is obvious. Tokyo natto on the left is very loose compared to Okame natto which is thick and almost gummy in texture.

Adding liquid seasoning such as shoyu or mentsuyu is the ultimate stringiness test as the weaker natto will decrease in stringiness when seasoning is added (left). Okame natto is going strong with the liquid seasoning added and becomes almost frothy when stirred vigorously.

On the pull test, the weaker Tokyo natto has a loose appearance and the strings do not hold the beans. In comparison, the Okame natto has strong thick strings which hold the beans.

Okame natto is the winner!

Concluding thoughts:
After running this side-by-side fermemtation, it is apparent that the natto starter used will have a big impact on the finished natto. Furthermore, the existence of "Niowa Natto", or low smelling natto tells me that there are different strains of natto used by the natto manufacturers. My assumption would be that older strains would be more stinky and may be linked to more stringiness. Okame Natto, which has been around for decades may be using an older, more traditional strain of natto that is more stringy and more stinky. This being based on my assumptions concocted by my perceptions are more for discussion than to inform you.

The other possible explanation is that the Okame natto package that I happen to pick up was fresher thus had a stronger livelier population of natto-kin.

The take home message to fellow natto makers is to weigh-in more on the natto starter if you have perfected the cooking conditions and are still getting poor results. As of now, my working hierarchy of making good natto in descending order of importance is:

1) Proper soaking of soybeans: At least 12 hours in the summer with a preference towards 16 hours, up to 22 hours in the winter. 
There are two test that can be done to check full hydration. First, split the soybean in half. The two halves should not have a gap in the middle. When fully hydrated, the two halves will touch in the middle. Second, foam will start to appear on the surface of the water. Probably due to respiration of the soybean getting ready to germinate.
When not properly soaked, the natto will turn hard when finished fermemting.

2) Proper steaming of soybeans: The soybeans should be steamed under pressure with a pressure cooker for 40 minutes. You can steam them in a regular pot, but expect up to 6 hours of steaming to achieve what can be done in 40 minutes steamed under pressure. By cutting corners here, the natto will turn hard when finished fermenting. The natto-kin might also have a hard time getting nutrients. I do not recommend boiling soybeans as the flavors will leach out into the water and the natto will lack flavor.

3) Fermenting Temperature: The standard is to ferment at 40C or 104F at least for the first 6-8 hours, when the natto start growing vigorously. You can tell that they are starting to grow by the pleasant nutty fermenting aroma. After this critical period, the natto will start to generate heat by its metabolism and you can be more relaxed about temperature on the last 10-12 hours of fermentation.

4) Natto starter: If you have the top three conditions under control and you are still not getting good results, this will more than likely be the culprit. I have used Mitoku Natto Starter in the powder form, but I have never made a stringy batch using it. Use frozen packaged natto, and try different brands if available as the results will vary as shown above.

5) More trivial, non-crucial matters: 
-Moisture and aeration. I usually use enough water from the bottom of the pressure cooker to wet cooked soybeans so water does not pool in the fermenting vat (about 3 spoonfuls). Having said that, I have forgotten to put the water and it still comes out fine. I have read online that natto needs lots of air, but I have found that this is not true. When the fermenting natto is exposed to air, the surface will start to dry out and harden and will look dark brown. I recommend the poked double cling method explained on the Homemade Natto Recipe.
-Adding sugar and/or salt: I have also seen this where sugar is added to make the natto happy. I have never used sugar and I get consistently good results. Same is true with salt.

I went a little longer than intended, but if this helps a fellow natto maker out there, my mission is accomplished.

Happy natto making and cheers to you for improving your well-being by eating natto!

Natto Dad


  1. How often did your try using a natto starter?

    1. Hi Dennis,

      I would say that the first 20 times or so I used the Mitoku natto starter sold by Cultures for Health. Never figured out how to make really stringy natto. I did make slightly stringy natto but was not satisfied with it. At the moment using frozen natto as the starter is my fool proof method. If you have any insights on using natto spores, I would be really curious to know!

  2. I'm going to my local, Asian market to try and find Okame Natto tomorrow. If not, I think there is a Japanese market not far from me and Korean market a few miles away. So I should be able to find some. Thanks for the review. I'm very hopeful to making some natto. I have about 26 lbs of small soybeans and I'm excited.

  3. Mahalo for your blog! I thought I would never find the kotsubo. The last batch that I made with regular beans turned out hard and didn't taste good m I will try with a work lamp for heat and kotsubo.

    1. Hi Corliss, glad I could help! I love Laura Soybeans. They are the best soybeans online and have not found anything comparable in stores. They are non-GMO and are family owned so that is all good for me. Mahalos for checking my blog.


  5. Thank you so much for this post. I eat natto with rice, seaweed and pickles on most mornings and always wondered if the natto purchased from the market would work as starter and am looking forward to trying this. Can you share what pounds of pressure was used for your cooker when cooking the soybeans?

    1. Thank you for leaving a comment! I believe most pressure cookers have an automatic relief valve that activates around 1.5 bars (~21 psi). My pressure cooker has a gauge and I can confirm that the weighted relief valve starts whistling (releasing pressure) around 1.5 bars. Please make sure to lower the heat to low heat just to maintain the pressure and prevent over-pressurizing the pressure cooker.