Making Natto from scratch (well, mostly)

I tried a new food, natto.  It’s fermented soybean food, mostly Japanese.  I have been bored with the foods I’ve had over the years repeatedly, so I’m branching out into new foods from different countries.  Japan seems to fit me to a tee, it seems.

The first thing to note is there is a soybean variety specific to natto, even though it will work with normal soybeans… they’re just too big to ferment all the way through without troubles.  There’s a type sold called sprouting soybeans, or simply natto soybeans, that I’ve seen so far at Laura Foods ( ) but I’m sure many other places have them.

It’s actually relatively simple to make them, much like tempeh and other soybean fermentations.  First, the starter (culture) can be the pure version sold by Cultures for Health ( ) or simply using a package of natto sold at the store would suffice.  Since it’s my first time, I went with the pure version sold by Cultures for Health, but once that is used up I’ll use samples saved from the previous batch made.

For the fermentation unit, I have one I’ve made that is multi-purpose.  It’s a cambro insulated food holder, with a 800w submersible heater, air pump/air stone, submersible water pump with a mini aluminum radiator outside connected to the water pump.  I have a temperature controller that controls the cooling & heating when the temperature goes above or below the target temperature by a certain number of degrees.
I’ll do a full document on it soon, but in a nutshell it holds the temperature within 2 degrees, and keeps the environment high humidity.  Without the cooling unit, 800w heater, or temperature controller, this is basically it:

Note: I used 3 cups, but less can definitely be used with no changes.


  1. Set incubator temperature to 104 degrees fahrenheit. (40 degrees celsius)
  2. First, wash the soybeans a couple of times to get the dirt out.
  3. soak the soybeans for 12 hours
  4. Drain in a sieve or colander
  5. Steam the soybeans.  I steamed mine in a pressure cooker, for 20 minutes at “high pressure”.  (yours may be different)
  6. Once the steam cycle is finished, let it naturally depressurize.  Don’t mess with the floater.  It should take about 30 minutes.
  7. Place freshly steamed soybeans into a sterilized bowl.
  8. Boil 10 ml of water, let cool for a bit then place one of the special teaspoons of natto starter into the water and stir.
    If using natto as starter, place 2 teaspoon of the natto into your beans then pour the water evenly over your beans.
    Stir immediately, carefully so as not to smash the soybeans.
  9. Spread the soybeans evenly across the bottom of the pan, don’t press them together as air will need to flow between them as they ferment.
  10. Place pan into incubator, and set a timer of some form for 24 hours.
  11. Once the 24 hours is finished, pull the pan from the incubator, visually inspect, place a lid on the pan (or aluminum foil if you don’t have a lid)
  12. Put pan in the fridge, and age the soybeans for a couple of days up to 1 week.
  13. That’s it!  Now separate into small serving containers and enjoy.

The natto doesn’t go bad, it can stand around for as long as you wish.  However, it does dry out.  I’m not sure, I’d imagine adding a sparing amount of water to it and stirring would probably rehydrate it, but I haven’t experienced that yet.

UPDATE September 9th, 2015

After finishing my first fermentation of natto, I’ve had it in my refrigerator for 3 days to age.  I’ve tasted a bean on the first and third night, and each time was different and tastier.  Tonight when I was scooping some out for breakfast tomorrow at work, the smell was wonderful.  The stringiness is starting to become more prevalent, and it’s all together a good thing.  On Friday I’ll fill 8 of the 8-oz air tight containers I purchased, so they can age without any worries of dehydrating from the naturally dry refrigerator atmosphere.

UPDATE May 12th, 2016

I left a few containers of natto in the fridge since I’ve originally made them back when this post was made in September 2015.  Yesterday I pulled a container out and tasted it — Delicious!  The flavor has become smoother, more complex.  The beans were more consistent texture-wise, with no hard spots.  It tasted like a mix of soy sauce, salt, steak flavor, and the bite of cheese.  I had to bring one as a side dish with my lunch today for work.  I’m glad I let it ferment that long to see how it’d taste, I’m definitely impressed.

2 thoughts on “Making Natto from scratch (well, mostly)

  1. Do you know not to expose the Natto to light? It will affect the nutritional quality by decreasing the vitamin K2. The people in Japan that it natto daily have some of the lowest rates of circulatory disease and the best bone health in the world. For more info google Chris master John and look at his vitamin K2 Research.

  2. Thanks, Dwight! I didn’t know light (or UV, etc) effected it but I guess it’s a good thing I keep it in a container and out of the elements when I’m fermenting. Thanks for letting me know, I’ll do some googling and learn some more on it!

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