Natto recipe

The Japanese dish Natto is perhaps the richest source of the elusive vitamin K2.  Read more here about why K2 is crucial for your health.

Aside from vitamin K2, natto also contains the enzyme nattokinase.  This is an enzyme that can help solve blood clots in the body and is slightly blood thinning.  It is sometimes compared to asprin, though without the negative side effects of asprin.  Nattokinase has also shown capable of breaking down the fiber-like proteins (amyloid) that can be found in diseases like Alzheimer’s.

In general we would not recommend eating soy.  But in the form of natto, where the organic bean has previously been soaked and then fermented, containing large amounts of K2 and nattokinase, the benefits far outweigh the possible negative side effects.

When you eat soy it is important to have a diet rich in iodine because the isoflavons from soy affect the hormonal system and may depress the activity of the thyroid.  Iodine is best gotten from fresh algae.  Dried are ok, but care has to be taken not to constantly overdose with them as they may affect the vitamin B12 levels in the body disfavorably.   Dried algae have an inactive form of B12 that competes with the active B12, read more here. 

To get sufficient levels of K2 you only need around 80g of natto every third day.  The K2 that you get from natto is mostly in the form MK-7 and that will tend to stay around in the body for up to three days.

Before you make natto, if you have never seen it in person, it may be of interest to buy some, so that you understand what the taste and consistency is like.  Asian stores often carry it.  Your homemade natto will likely be somewhat different as you may be using different soy beans.  To make natto small soy beans are usually used, but you may use other types.  Usually it is easier to get a hold of larger and sweeter beans, and they still work well.  Though smaller beans make it easier for the fermentation to penetrate into the center of the bean.

Also, if you can get ready made natto you will also have some bacteria (bacillus subtilis, natto bacillus) that you can use for your own fermentation.  But it is recommended that you get the bacteria spores separately.  That way your natto will be stronger, have a greater quantity of K2.

The advantage of making your own natto is that you can be sure that it is organic, without glyphosate (which disturbs the intestinal flora), not genetically modified, and you can soak the beans so that you will minimise the amount of phytic acid.  Soaking soybeans for 12 hours in regular room temperature water reduces the phytate content by between 23 and 30% depending on the bean (1).  But as you will see in the recipe, you can improve this by extending the time and taking extra care to further improve the soaking environment.

Read the recipe below or download it here as a pdf.

How to make your Natto

What you need:

  • Organic soy beans
  • Water
  • Nattobacillus (bacillus subtilis, bacteria or spores for the fermentation, or mix in some already made natto)
  • Glasses or cups to keep the natto in portions
  • Pressure cooker (or large pot)
  • Bowl for mixing
  • Spoon
  • Tray (where all the cups fit)
  • Lamp with a regular lightbulb that heats up
  • Large ice box with lid (where the tray and lamp fit inside)
  • Newspaper
  • Paper towels
  • Scotch tape
  • Thermometer

1. Soak the beans

Soak the organic soy beans for 24 hours.  The optimal way to do this is to have warm water, not warmer than 55C (131ᴼF).  Add something sour to the water, like lemon juice, vinegar, or ascorbic acid to lower the pH value.  This will create a perfect environment for the enzyme phyase to work on eliminating the phytic acid.  Change the water a few times.

If you want you can also grind a few rye grains and add them to the water.  Rye has high amounts of the enzyme phytase, that breaks down the phytates.

2.  Cook the beans

Wash and cook the beans.  They should be soft enough to eat.  You should be able to squish it between your fingers.  If you use a pressure cooker it may take 30-60 min depending on your cooker.  Use a pressure cooker if you can, because otherwise you may need 9 hours (!!) to cook the beans to get them soft enough.  If the beans are not soft enough, it will be difficult to get a proper fermentation, and your natto will not be stringy, as it should.  This is an important step.  The beans need to be soft enough for fermentation to take hold.

3.  Prepare the fermentation cups

Pour boiling water in the cups to disinfect them.  We do not want other types of bacteria to compete with the ones we will add.  Also disinfect the bowl and spoon where you will be mixing the beans with the bacteria.

4.  Prepare the fermentation box

Put a lamp and a thermometer inside the ice box.  Turn on the light and let the lid be a little open, just so that the temperature inside of the box will stay around 39-40C (102-104F).

5.  Prepare the beans for the fermentation.

Pour out the water and put the beans in the mixing bowl.

If you have already made natto mix some of it with water and then mix it into the beans.  Make sure that the beans are still warm but not boiling hot.  They should be around 40-50C (104-122F).  Work quickly to put them into the cups.

If you have bacteria then follow the instructions on the package and then mix the diluted mixture into the beans.  Divide them into the cups.

Place the cups on the tray.  Put two layers of paper towels over them and wrap the whole tray and cups in two sheets of newspaper.  Use the tape to hold it together.  Do not use plastic wrap as the bacteria need oxygen to ferment.  Alternatively you can put plastic wrap on them and punch little air holes with a tooth pick.  Or, you can put damp, clean cloths around the cups.

You want there to be some oxygen, but you do not want to beans to dry out.

6.  Ferment

Place the wrapped tray into the fermentation box and check now and then to make sure that the temperature is around 40C (104F) for the first 10 hours.  If the temperature is too low, it will not work.

After 10 hours you can increase the temperature to slightly below 50C (122F) and keep it there for 4 hours.

After a total of 14 hours you lower the temperature to 39-40C (102-104F).  If you do not lower it the beans will dry out.  Keep the fermentation going for 10 more hours.

After a total of 24 hours you can turn off the light in the fermentation box and let the beans slowly reach room temperature.

7.  Keep them in the fridge for 24 hours

When you open the newspaper you will smell a cheesy sort of smell and there should be a glue like substance on the beans.  You will notice the glue like substance especially if you start mixing the beans.  You can cover each cup with plastic and keep it in the fridge for 24 hours.

8.  Store the natto in the freezer

After 24 hours in the fridge you may store the natto in the freezer.  In the fridge natto will keep for a week.  You may see little white dots forming on it.  This is normal and not dangerous.  In the freezer it will keep much longer.

You can download the natto recipe here as a pdf-file.

Natto Making Schedule

Because of the 24 hour fermentation it can be wise to plan ahead when you start soaking your beans.  Here is an example of a natto making schedule.

Thursday  8 pm start soaking the beans

Friday       8 pm cook the beans

Friday     10 pm place the beans in the fermentation box

Saturday   7 am increase the temperature to 50C (122F)

Saturday 10 am lower the temperature to 40C (104F)

Saturday   7 pm turn off the light

Saturday   9 pm place the natto in the fridge


Elisa Noemberg Lazzari Karkle, Adelaide Beleia, “Effect of soaking and cooking on phytate concentration, minerals, and texture of food-type soybeans”, “Efeito de maceração e cocção sobre concentração de fitato, minerais e textura em sojas para consumo humano”,Ciênc. Tecnol. Aliment., Campinas, 30(4): 1056-1060, out.-dez. 2010.

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Leave A Reply (7 comments so far)

  1. casquette supreme
    1 year ago

    Merci pour cet article

  2. Patricia Roth
    7 months ago

    Thank you so much. I love natto and would like to make my own so I can be assured of its quality and not have to keep going to the store as I’m a bit of a shut in. I loved your explanation.

    • Admin
      5 days ago

      Yes, it is great when you know you can have organic (non-GMO) ingredients. And it also ends up becoming cheaper to make it and always have a good source of vitamin K2.

  3. Bob Wareham
    1 week ago

    Thank you for the information I have ordered the powder from Japan to make Natto and with your instructions, I am going to have a go using my slow cooker crock pot.

    Thank you Bob

    • Admin
      5 days ago

      Great! Good luck! And make sure you cook the soybeans long enough (if cooked without a pressure cooker it can take up to 9 hours!). If the beans are not quite soft, it will be difficult for the bacteria to grow and penetrate them. (I think that this may be one of the most common problems people run into.)

  4. Bob Wareham
    3 days ago

    Natto Fail
    I have followed your instructions:
    Clean and wash soybeans (not organic this time)
    1.) Put beans in slow cooker for 24 hours to cook until soft
    2.) Wash beans and move to small clean container
    3.) Add powder from Japan (small bottle with small spoon Natto powder)
    4.) Move container to yoghurt maker to ferment for 48 hours at 37c
    5.) Problem I end up with beans that look ok they have a white film on them but smell of ammonia my wife said it takes her back to Nappi times
    6.) All items were scolded with boiling water to destroy any other bacteria

    Any help, please Bob

    • Admin
      2 days ago

      Hi Bob!
      Natto can certainly be temperamental. Do not be discouraged. I do not know of anyone who always makes perfect batches, but over time, after tweaking, most batches are turn out well.
      So, some key points:
      – The beans need to be soft (you should be able to squish them between your fingers and turn them into a pulp that way). Otherwise the bacteria will not be able to get the nutrients they need to ferment.
      – The powder is usually dissolved in water before mixed with the beans. And the beans should not be boiling hot at the time you mix in the solution with the spores (max 50C). And if it does not seem to work you can try getting a commercial natto and use some of it as a starter as well.
      – Then, and here is an important part, the temperature should be close 38-40C in the beginning. If it is too low, it will usually not work.
      – If you are using a yoghurt maker, check what temperature it is producing in reality with an external thermometer. Sometimes you will note that it varies with the outside temperature (different in summer and winter).
      – Also, you will need a little bit of air to get into the beans, so that they have some oxygen for the fermentation (this is different from yoghurt). But you do not want to dry the beans out, so only a little air.

      I have heard that adding some molasses (just a tiny little bit) can help the fermentation get going. But I have not tried this yet.
      I hope this can help. Natto is such an awesome source of scares nutrients, but it is a bit of an art to make it.

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