How to Make One Year Fermented Miso

by Kaitlynn Fenley

We make miso by mixing soybeans, or other legumes, with the fungus Aspergillus oryzae and salt, and allowing fermentation to occur. Usually, miso ferments for six months to a year. It can also be made with rice, wheat, and oats incorporated. Miso contains a lot of beneficial vitamins, minerals, proteins, fiber, and isoflavones. Come learn how to make miso with us!

The History of Miso

Different regions of Japan, China, and Korea all make different types of Miso, incorporating various local ingredients like barley, brown rice, adzuki beans, mung beans, and even hemp. Miso as we know it originates from Japan. Some scholars think that China or Korea introduced miso to Japan around 600 AD. A lot of cuisines are flavored with miso, the most popular and well known is Japanese miso soup. 

Miso as we know it originated anywhere from 10,000 to 5,000 years ago. Scientists think that miso was made from fermented grains, shellfish, fish, and meat preserved in salty seawater, later, evolving into a product made with beans.

How is Miso Made?

Miso is made with koji. Koji is the common term, but the taxonomic name is Aspergillus oryzae, a fungus. The important factors that contribute to miso quality and flavor are fermentation temperature, fermentation time, total salt concentration, Koji quality and variety, and substrate used (type of grain or legume used). You can find koji online, or at an Asian market. You can really manipulate the flavor of miso by adjusting the ratio of koji used. More koji means sweeter miso, less koji means more savory miso.

I’m not going to dive into miso mathematics rationale too much, because it’s a bit more complicated than measuring salt for fermented vegetables. Just know that I make my miso with the intent that the final total salt concentration of the mixture is usually between 12%-17%. This is what I like to do: I cook a bunch of lentils, then weigh the cooked lentils with the koji (in grams), multiply that weight by 0.17 and add the result in grams of salt.

Miso can be made using any type of legume and/or grain. My favorite kind is lentil miso, and I’m currently experimenting with a sprouted lentil, buckwheat, and oat miso. Lentil miso just comes out with a silky-smooth- like texture that’s a little bit different from soybean miso. I like to blend my miso into a smooth paste after fermenting using my blender, but you can also leave it as is for miso with more texture. 

Making miso is pretty simple, the most important step is… you guessed it… weighing your ingredients! Here are the ingredients and supplies you’ll need:

  • Large glass Jar
  • Plastic Wrap
  • Sea Salt
  • Lentils (or any legume)
  • Koji (Aspergillus orzaye)
  • Cheap Vodka (for cleaning)
  • Kitchen Scale
  • Large Bowl
  • Potato Masher

The Timeline

Preparing the miso will take two days, and the fermentation time is 365 days. You can taste test and eat the miso anywhere between the 6 months and 1 year mark, though.

To start the process, you’ll need to soak the lentils for 12 hours. After soaking you cook the lentils until they are soft enough to mash with a fork or potato masher. Allow the lentils to cool to room temperature, then mix in the koji and salt. Last, you pack the miso into the jar, cover it with salt and plastic wrap, and put it away to check after three months.

When checking the miso, you want to look for signs of surface mold. If blue, black, or green mold grows on the miso mixture, it’s no longer safe to eat and should be discarded. If you follow all the directions, clean your equipment properly, and weigh the ingredients this should not be an issue. If everything looks fine, remove the plastic wrap and turn/stir the miso with a clean spatula. Smooth and pack the miso back in and place a clean piece of plastic wrap to tuck the miso in. Last, you’ll allow it to ferment for 3 to 9 more months. I like my miso fermented for a year the best. I pulled the miso pictured here at 8 months, and it was delicious.

The Microbes in Fermented Miso

Koji is the starter culture we use in miso fermentation. It is rice with spores from Aspergillus orzaye fungus. This is the starter, however, the total desirable microbial composition usually includes:

  • Aspergillus oryzae 
  • Tetragenococcus halophila
  • Enterococcus faecium
  • Lactococcus spp.
  • Lactobacillus spp.
  • Pediococcus spp.

Bacillus spp. are sometimes found in miso, but their growth is inhibited by bacterocins produced by Enterococcus faecium. Bacillus spp. are halotolerant to light halophiles, so they love to grow on media with about 15% to 20% (w/w) NaCl. Bacillus species often reside on rice, so their presence makes a lot of sense, but is not ideal.

The rate at which Aspergillus oryzae grows is largely determined by the temperature of fermentation. Aspergillus oryzae can tolerate extreme conditions, like high salt concentration, if all of the other conditions are ideal. Ideal fermentation temperature is cooler, around 70 Degrees F. Some say that the best miso is started in the winter, in order to cycle through cold winter temperatures, then slightly warm spring temperatures, then to finish off in warmer summer temperatures. This probably compliments and promotes the different phases of fermentation that occur in miso.

Since Aspergillus spp. are fungi they are dependent on decomposing their surroundings for nutrition. To rely on surrounding substances for nutrients, they release different types of enzymes such as amylase. These enzymes are capable of breaking down organic matter into simpler compounds as a food source that the fungi can absorb through hyphae. This is what the fungus does to beans in miso fermentation, creating fermentation byproducts beneficial for digestive health.

The Health Benefits of Fermented Miso

Some research has shown that miso can aid in the prevention of radiation injury, liver cancer, breast cancer, and intestinal tumors in animal models.

This study was conducted to understand why the citizens of Okinawa Japan have such a long life expectancy. In this area of Japan, miso soup is a major staple of the average diet. Miso is full of antioxidants that may help reduce oxidative stress and thus the risk of cardiovascular disease, cancer, and some chronic diseases. So the long life expectancy makes sense!

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How to Make One Year Fermented Miso

Miso is a long-fermented paste produced by fermenting soybeans or other legumes with the fungus Aspergillus oryzae and salt for one year. It can also be made with rice, wheat, and oats incorporated. Miso is packed with beneficial vitamins, minerals, proteins, fiber, and isoflavones. Come learn how to make miso with us!

  • Author: Kaitlynn Fenley
  • Prep Time: 60 Minutes
  • Cook Time: 15 minutes
  • Total Time: 1 hour 15 minutes
  • Yield: 35 Servings 1x
  • Category: Fermented Foods
  • Method: Fermentation
  • Cuisine: Japanese
  • Diet: Vegan

Ingredients

Scale
  • 750 grams cooked lentils
  • 200 grams koji
  • 160 grams sea salt*
  • 50 grams sea salt, set aside

Instructions

  1. Soak about 350 grams of lentils overnight, for 12 hours. 
  2. Rinse the lentils, then cook them for about 15 minutes until they are tender. Do not overcook the lentils. 
  3. Drain any excess water and allow the lentils to cool for 15 minutes. 
  4. Measure out 750 grams of cooked lentils into a clean bowl. (You may have a bit of lentils leftover)
  5. Add the koji and the salt to the 750 grams of cooked lentils.
  6. Mix well using gloved hands or a potato masher. You want to crush all of the lentils into a paste, kind of like a cookie dough consistency.  
  7. Prep the jar or container you plan to use as a fermentation vessel by cleaning it with vodka. Pour a bit of vodka in a clean jar, place the lid on the jar, and shake it for a minute or so. Remove the lid, dump the excess alcohol, and allow the jar to air dry.
  8. Take a large chunk of the miso mixture and form it into a ball with your hands. Then slam the ball into the bottom of the jar. Repeat until all of the miso is in the jar. Press down on the mixture and make sure it’s tampered down.
  9. Sprinkle the 50 grams of set aside sea salt across the top of the miso.
  10. Clean the sides of the jar with a paper towel dipped in alcohol. 
  11. Place a piece of plastic wrap (or parchment paper) in the jar, tucking it tightly around the top of the miso. 
  12. Place a fermentation weight on top of the plastic wrap and place a lid on the jar. 
  13. Store the miso in a cool dark place for 3 months.
  14. At the three month mark, check the miso. Remove the plastic wrap, stir and turn the miso, then pack it all back into the jar. Clean the sides of the jar with alcohol and place clean plastic wrap, weight, and lid back in the jar.
  15. Allow the miso to ferment for nine more months at a moderate room temperature in a dark cabinet. 
  16. After fermentation is complete, you can transfer to smaller jars and store them in the fridge. 
  17. For a smooth miso paste, blend the miso in a blender/food processor before storing it in the fridge. 

Notes

*Miso can be made with anywhere between 12 to 17% salt added. For lower sodium use 114 grams of salt

  • Ideal temperature: 60° to 70° F.
  • It’s easiest to use a jar or container with a wide mouth opening.
  • No, you cannot use canned beans. 

Keywords: miso, bean paste, koji, fermentation


References: 

Frias, Juana & Martinez-Villaluenga, Cristina & Peñas, Elena. (2016). Fermented Foods in Health and Disease Prevention.

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12 comments

Terry Stephen November 25, 2020 - 5:07 pm

Hi Kaitlynn, your blog is truly excellent.
Have a question in regard to the miso. In your article it’s not fully clear to me that if the miso grows green or blue mould, do you remove it, stir the miso and them reseal it with cling film ? Or did you discard all the miso totally and start again?

Reply
Kaitlynn Fenley November 26, 2020 - 7:44 am

Hey there!
Thank you!
I just elaborated more in that paragraph and updated the blog. If blue, black, or green mold grows on the miso, it’s not safe to eat and needs to be discarded completely. I’ve never experienced this myself, so if you use the proper salt concentration and clean equipment this shouldn’t be an issue.

Reply
James March 14, 2021 - 10:29 am

Hallo there !

Thank you for the detailed instructions and knowledge about miso and its preparation.

In reading that you are experimenting with sprouted lentil miso recipes, the curiosity arises if it is necessary to cook the lentils at all, and if the recipe can be made with raw lentils?

Thanks!

Reply
Kaitlynn Fenley March 18, 2021 - 8:17 am

Yes it is necessary. Regardless of the type of legume used, all must be cooked before making miso. The cooking step is essential to prevent unwanted microbial growth.

Reply
Uyum April 19, 2021 - 9:28 am

Hi,
A quick question. I’m at 3 mm months mark. After mixing the miso (I assume the salt on the top will be mixed as well) before closing it again, do I put salt on the top again?

Reply
Kaitlynn Fenley April 20, 2021 - 12:41 pm

You can, but it isn’t necessary. Since it’s been fermenting for a while at this point, there’s less concern about surface mold. You do need to re-seal the top surface with plastic wrap though.

Reply
timur sila November 30, 2021 - 12:54 pm

Can I use leftover miso to inoculate another batch?
Or store bought?

Reply
Kaitlynn Fenley November 30, 2021 - 1:22 pm

You can incorporate leftover miso, but it cannot be used in place of Koji. You still need Koji for proper preservation and flavor development.

Reply
Nick K January 13, 2022 - 6:15 am

Hi Kaitlynn,
I absolutely love your recipes and the time you take to educate everyone about what’s going on on the microbe level. I can only hope it’ll all be in a book one day!
Quick question about the shelf life of the miso after the 12 months. How long would you recommend that it is good to keep for? I would like to have a constant supply of it so am wondering if I can just make a double batch annually, or if I should do 2-3 smaller batches spaced throughout the year. And does it need to be stored in the fridge after the 12 months or can it continue in the cool dark place?
Thanks so much for the time and effort you put into everything!
Nick

Reply
Kaitlynn Fenley January 13, 2022 - 3:53 pm

Happy to hear you are enjoying our recipes! You can make a big batch annually, it keeps pretty much indefinitely in the fridge… so yes, it needs yo be stored in the fridge after the 12 months of fermentation. Let me know if you have any more questions!

Reply
Lisa January 31, 2022 - 7:23 pm

I am so stoked to try this! Here is my question: is there any benefit to tossing “old” miso or other ferments after a certain date, even if they still look and taste fine? I have heard that the percentage of beneficial microbes starts to reduce after a while. Should I start fresh even if I haven’t finished a batch, in order to reap more health benefits from a younger ferment?

Reply
Kaitlynn Fenley January 31, 2022 - 7:53 pm

I’ve personally never tossed an old ferment if it still looks and tastes fine. I even use fermented vegetables that go a little soft after years in the fridge. I usually cook with very old ferments since the texture isn’t great raw, I like to add them to soups, stews, braises and breads. Then I enjoy newer, fresher ferments raw.

Reply

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