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2020, Jul. 4

Miso S.O.S

'Is this mold?'


'Is this mold?'


After a few months from my Miso workshops, I sometimes receive inquiries from the participants. 98% of its' topic is if their Miso has mold on the surface. In the end, we find out that most of them aren't mold. Interestingly, most people think everything grows on the surface is mold.


It might be a bit mean of me that I don't want to give them the answer right away. So, I always ask people back, 'how does the mold-ish thing of the surface look like?'. It's for them to take a chance to see and find out what they can be by themselves because I want people to get used to microorganisms. Every microbe isn't harmful, and they are there because we made the environment for them to grow.


Fermentation needs the work of microorganisms. So as spoilage. Whichever we call, we can make environments for them to like or not. 

I hope this page helps you find out what your Miso has produced.



If you want to find out the solution and cause of the situation, please check these below.

Solution >>   Cause >>



① My Miso has something

fluffy and hairy and

the color is white, black,

blue, or grey!!

It belongs to mold, but no worries, your Miso is still good. Just scrape all the mold off. And wipe the container. 

Though you need to scrape a bit of the Miso off, it still safe to eat the inside after mixing well. Mold only grows anywhere moisture and access to air, so no molds can survive inside the Miso.

Solution >>   Cause >>


② My Miso has something

not hairy but rather 



It belongs to the yeast, not mold. No worries, yeast doesn't harm you but rather helping your Miso become flavorful. So, if you find yeasts, they can be mixed into your Miso. Check well if it doesn't have any hairy part because yeast can collaborate with mold if you let it sit for a long time. Then check the flavor. 


The way to check the flavor is for advanced fermentation learners, but please have a try. Firstly, take a bit of the yeast on your tongue. Close your mouth and let the air in your mouth push to your nose. It's like when you taste the flavor of the wine. You may notice some similar fruity flavor to wine or bread from the yeast. If you don't like the scent at all, just spit it out and scrape all of the yeast off from the surface.


I prefer light flavored Miso, so when I see some yeasts on the surface of Miso, I scrape off the most of it. If I only find a bit, I don't mind mixing them all.

Solution >>   Cause >>







③ My Miso has something

transparent or

dark brown liquid!!



No worries, your Miso is safe and beautifully fermenting.


Is it transparent? Or it has a color like soy sauce? Try licking it a bit. 


If the color is transparent, you taste Umami with sharp saltiness. If the color is like soy sauce, it tastes mellow soy sauce. The latter one is called Tamari and the former one is going to be Tamari later. It's known as a glutin free soy sauce. You can even have some for your salad, or Tofu, as a kind of seasonings.

Even if it's tasty, you shouldn't be greedy. Miso also needs it. When your Miso is under the Tamari, Miso doesn't touch the air so it means it's protected from mold. Share the Tamari with your Miso.


④ My Miso has

something like a screen

floating on the brown liquid!!


So, the brown liquid is Tamari. (See ③)

When you have plenty of Tamari, you may see something white floating which is not hairy nor lumpy but it's rather like a screen. It's kahm yeast. If you home-make sauerkraut, you often see this. It doesn't harm you but can be taken away if you don't like it.

If I see kahm yeast on my Tamari, I don't take them away. Because I don't want to waste Tamari. I harvest both Tamari and kahm yeast in a small bottle and keep it in the fridge.


⑤ My Miso has

something like

white crystals!!


If you find something like on the photo above, it's crystals of Amino acid or salt. It's totally edible. The crystal of Amino acid can be found in the aged hard cheese like gouda cheese.


⑥ My Miso has

something I see on

my Kombucha!!


It might be a rare case but anyway I'll share. I also found it in my friend's Miso.


It happened to my ten months-aged Miso. It was after a scorching summer in Japan. When I opened and looked in the container of Miso, I saw a trace of Tamari, which seemed dried out while in the summer. However, the trace was quite thick and sticking compare to the other years when I had Tamari. I checked my other Miso container and found a bit of Tamari and a thin but strong film-like thing. I thought it's a bit strange but tried the Tamari and found it's tasty but more acidic than usual.


I wondered what has happened to my Miso. I thought, maybe, acetic acid bacteria joined the fermentation. Because I found the screen as I see in my Kombucha and the Tamari was a bit tangy. The SCOBY I found on my Tamari was not thick but a bit hardy when I pulled it. I knew that the SCOBY of Kombucha could be used as synthetic leathers when it's dried. So, the thing I found was like that, but I might be wrong.


If you encounter a similar situation, please let me know how you think. 

By the way, the Miso of that year was beautiful.



⑦ My Miso has

some white stuff inside.


Inside? If you see the white things inside of your Miso and it's all over, I think it's rice Koji which you used as an ingredient.


The store sold Miso is too smooth, so that it's hard to find rice flakes. If you home-made Miso, the shape of rice Koji remains for a half year. So, when you make Miso soup, you see the rice Koji floats. After fermenting a year, you may find the rice koji dissolve in the water.



I wonder if you found the right answer for you and the Miso. Homemade Miso is like a living thing. It goes through some changes, so I hope you can enjoy these changes. I don't check the situation of Miso so often, but every time I open the container, I appreciate how my Miso changed.


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