Miracle Food from Japan – Easy homemade Natto

nattoreadyWhat is Natto?

With the risk of sounding trite.  You either love natto or hate it.  In Japan natto is regularly eaten as a breakfast food.  I still remember a family stay in Japan, where the little three year old daughter chowed down on a humongous plate of natto – every morning.

Natto, to me, has the taste and smell of a finely ripened cheese (without the cholesterol) – lots of umami in other words.  To others, it is disgustingly smelling, vile, pungent and slimy.


Traditionally, you add a bit of soy sauce.


and some Asian hot mustard.  The mustard is a lot stronger than what we get here.  It needs to be reconstituted in water, the instructions are on the container (2 tbs hot mustard powder with 3 tbs water).  Also, add some welsh onions, scallions, etc as a dressing on top.

Some interesting facts about natto:

  • part of Japanese diet for thousands of years
  • made with the help of Bacillus subtilis for fermentation
  • richest known natural source of vitamin K2
  • contains nattokinase which may aid in the fight against heart disease and Alzheimer

What to use as a natto starter?

There are really two ways.  The first is to simply use the pre-packaged styrofoam cups sold in Asian stores.  They are intended for consumption and come with a little package of mustard and soy sauce to mix with.  I would suggest you buy one of these first and try it to see if you like it and do the first few ferments with this till you get the hang of it.  I generally use the entire package, although I read that it should still work with about 1/4 of the package as a starter.  A pack of 3 costs around $2-3 dollars and should get you, maybe up to 12 ferments.


Another option is to use the actual spores.  Spores cost around $12 for a small container (making up to 30 kg of natto).  You mix 10ml of sterilized (boiled and cooled off) water with 0.1g of spores (using a small measurement spoon that comes with the set).


What types of beans?

While you can make natto with various beans such as adzuki and black beans, soy beans seem to give the best consistency.

Another trick to use the smallest soy beans you can find.


These soy beans are for sprouting, a good choice.


These beans are also smaller; again, a good choice.

big soy

The beans are the typical soy beans sold in the US, larger in size.  These will still work but are not optimal.

What else do we need?


A container to hold the beans.  I prefer glass such as these rectangular glass containers.  I stack them in my fermentation container with some chopsticks balanced on the lower container to allow for some air circulation.


I generally cover the containers with some aluminum foil with small holes poked into it.


Before you get started, wipe everything down with alcohol to disinfect it.  Extraneous bacteria are a big reason why your fermentation might fail.


A remote thermometer will help you keep an eye on the temperature during the fermentation.  It should generally be around 100-110 F.

What about the fermentation container?


I use a styrofoam box with a lamp socket suspended in the side wall.  A 15W bulb generally keeps the temperature at 110F during the winter (use 10W in the summer).  I also keep a little mug filled with water in the corner to provide for humidity.  You should also keep a remote thermometer in there to keep an eye on the temperature.

You may be able to use a yogurt maker instead.

What are the steps?


1) First, we need to soak the beans.  About 24 hours is a good goal.  Skim off any shells, husks that come off the beans.


2) Next, we need to cook the soy beans.  I will generally pressure cook them for 10-20 minutes.  You want them fairly soft so the natto can penetrate the beans.  I read that streaming them is far superior, so I will give that a try soon.  You can put a metal inlay steamer in pressure cooker and steam for 40 minutes.  The beans are supposed to develop a much stronger taste doing this.


3) We then drain off the water.  The beans should stay slightly moist but not soaking wet.  Too wet and the natto will be crowded out by other bacteria.  Too dry and the natto will not grow fast enough.


4) For this fermentation, I used packaged natto as  a starter.  It should be thawed before adding to the cooked natto.


5) Mix together the cooked soy beans and the starter.  The beans can be warm, but not scalding hot.


6) The mix is then packaged in the glass containers and covered with aluminum foil (punctured with holes to allow for air circulation).


7) Finally, we put everything in the fermentation box and in 24 hours, natto is ready.  An additional step is to age it in a refrigerator for up to one week to allow for added development of flavor.

The most important factors are:

  • Cleanliness – clean everything thoroughly with soap and wipe down with alcohol if you want to be extra sure.
  • Temperature – keep between 100 to 110 F, with 104F being optimal.
  • Small, well cooked beans to allow for natto penetration.

Below is a video description of the steps.

5 thoughts on “Miracle Food from Japan – Easy homemade Natto”

  1. Hello,
    Thank you for your detailed instructions on making natto. I followed your directions with a few modifications and my first attempt was successful. My modifications included using: black beans, boiling water to sterilize equipment, plastic wrap to cover the glass dish, and a heating pad as the heat source. Both my husband and I are liking the natto for breakfast, over rice with a soft-boiled egg or chopped scallions. Questions: How often do you typically eat natto? How much in a typical serving? Thank you again.

    • Awesome. Have not tried with black beans, but you have peaked my interest. I usually make it every 3 weeks when the g/f is out of town (she doesn’t like the smell) in a bigger batch and then eat it in small amounts (half a cup) on a daily basis.

  2. Thanks for your interesting detailed article on making natto at home! I eat natto every day because of the high vitamin K content since dutch newspapers warned that half of our population has vitamin K deficiency mainly due to a lack of consumption of green vegetables and informed us about the serious consequences for one’s health
    Just like you, I love the stuff now! I buy it in asian supermarkets, but have grown a bit suspicious:
    do you know something about the quality of the soy beans in the natto sold in asian supermarkets? Are they treated with pesticides? Are they manipulated? Where are they from?
    Does a yoghurt maker guarantee exact the right temperature during the fermentation? Is it easier to use than that container you use (requiring constant supervision) Is there other special equipment available for fermentation?
    I am going to try your procedure with soy beans from the health store.
    Thanks against and thanks in advance for your answer.

  3. Thank you for posting the recipe for natto. I am happy to hear that I can use my store purchased natto as a starter. My only concern would be for the alum foil cover, it could leach metals into the food. I will use unbleached parchment paper instead. And I would only use organic soybeans (non-gmo).

  4. hello to all!i have two questions.
    1/ has anyone ever tried using styrofoam containers to ferment the natto in place of glass or metal pans?
    Also, soya seeding or sprouting beans can be used in place of regular soya beans?


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