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2020, Jul. 4

Why is my Miso moldy?


'All right. Let's have a check on my first homemade Miso!

I've been letting it sit for a half year, so I wonder how it has been doing.


Oh ooh, something horrible growing on the surface.


Oh no, what should I do!?'

No worries, even if you see something ugly on your Miso, you can still eat your Miso after scraping those off from the surface. It's natural for some microorganisms to grow on the surface of Miso. However, you might don't want to see them.


If you want to avoid letting something overgrowing on your Miso, please try my method. Fermentation needs the work of microorganisms, but we can always create a suitable environment for not seeing a disappointing situation.



For the person who wants to know what happened to your Miso, please check this page first.  Miso S.O.S 'Is this mold?' >>



Anaerobic fermentation

and aerobic fermentation



Firstly, I'll write about the environment of fermentation. There're two types of fermentation that is 'anaerobic fermentation' and 'aerobic fermentation.' The former means that fermentation happens by the microorganisms which don't need oxygen. And the latter fermentation occurs with oxygen. It sounds a bit confusing because we aren't familiar with what cultures need oxygen or not. So, simply, you can think as if your ferments are alive when they touch the air or not. If you are going to try new fermentation, it's good to know if it is 'anaerobic' or 'aerobic' because it changes the game.




For example, can you tell which ferment is anaerobic and aerobic from below?

Sauerkraut   Kombucha



Let's see how to make them.



The process of making Sauerkraut is like this. Chop cabbage and mix with 2% salt. If you squeeze the cabbage, you'll see some juice come out, so keep mixing and pressing the cabbage for a while. Then put the liquid and the cabbage in a jar and place a weight on the top. It needs to be heavy as it submerges all the cabbage under the juice. Let it sit for around a week. Then you'll see the cabbage changes the color to yellowish, and the liquid becomes cloudy.  Try the taste, and you'll find the tangy taste though you didn't put any vinegar.



Kombucha needs a SCOBY, which looks like a gummy mushroom to start the fermentation. SCOBY stands for symbiotic colony of bacteria and yeast. It means SCOBY is a home of many microorganisms. Firstly, make tea and dissolve sugar. Cool it down, then put the SCOBY and the tea in a jar, and cover the top with a cloth. Let it sit for around a week, and you'll see a second scooby forming on the surface of the tea. The tea taste becomes tangy and fruity. There's a way to move on to the second fermentation, but let's only focus on the first fermentation here.



So, have you got your answer?



Sauerkraut is anaerobic fermentation and Kombucha is aerobic fermentation.




I tell you the reason. Sauerkraut, the cabbage was submerged under the juice, so it didn't touch the air. Most of the microorganisms which make cabbage rot are in the air, but they weren't able to reach the cabbage because of the salt brine. So, we created a favorable environment for lactic acid bacteria, which can make sauerkraut. This type of lactic acid bacteria can live in the salt brine. So, that's why the cabbage became sour safely. Sauerkraut is one of the forms of anaerobic fermentation—no success with access to oxygen.


Then, next Kombucha. So, the first SCOBY is under the tea, but the new SCOBY formed on the surface where it has much oxygen. As I introduced, SCOBY is home to microorganisms. They do their work by using oxygen to breakdown nutrients in the tea. So, they need much oxygen, that's why we cover the jar with a breathable material. 




I wonder if these made sense for you. When I write the process down, it seems complicated but more simple if you do it.


Is Miso

anaerobic or aerobic?

Let's go back to the main topic, homemade Miso. Which fermentation does Miso need?


In general, we press the pre-fermented Miso in the container and put weight on the top to make Tamari goes up on the surface. The weight and Tamari aren't necessary, but they are handy if you don't want to see anything ugly on the surface of Miso. Yes, as you may have guessed, Miso is anaerobic fermentation.


Some people may think of fermenting Miso in an airtight container, but that's not a good idea. Because Miso produces gas while it's fermenting, so it will blow your vessel, and also, the carbon dioxide gas may make your Miso smell a bit alcohol-ish. 


Sauerkraut also produces the gas, so we need to release it frequently. We need to make an environment to avoid our ferments touching too much air and also to release the gas. It may sound complicated again but don't forget that our intelligent ancestors have already shown us useful ways of making beautiful Miso. 





Make an

anaerobic environment

for our Miso.


I've already mentioned a little; I'll introduce the environment for making tastier homemade Miso. If you can make this environment, it decreases the chance to come across the ugly surface on your Miso. (This way is what I always do and there might be another way to do.)

① Placing a weight on the Miso to cover the surface.


Please remember that placing a weight is very important for Miso.

<The role of weight>

・Avoiding the surface of Miso touches air as much as we can.
→ It prevents non-necessary mold and yeast overgrowing on the top.

・Pushing up Tamari on the surface.
→ It also helps Miso staying under the liquid and hiding from the air.

・Sometimes, the gas may produce some air pockets inside the Miso but the weight can press them down.
→ If you let the air pockets in the Miso, you'll grow more chance for non-necessary microorganisms to make a home.



(Left: Miso with a weight. Right: Miso without a weight.)




I often see some people placing the weight only a part of the surface and they have some stuff growing on the top.


I don't say you can't make Miso without weight but if you want to avoid the ugly look, it's good to place a weight carefully. Please remember that you didn't ruin your Miso even you found molds having a party on the top.



<How to place the weight>

1. Make a bag of salt.


Traditionally, the Japanese used a circular wooden board and rocks as a weight, but these days it's hard to find them. So, simply, put salt (half amount of Miso) in a plastic bag to make the weight. It can fit any shape of containers. 


2. Put a plastic wrap on the surface of Miso and then the salt bag.


3. Take a close look at if the weight covers the surface of Miso.




* I can't guarantee that this way prevents the ugly look forming on the Miso for 100%. What I wrote was one of the effective methods. There're some participants of my Miso workshop says they don't see anything grow on the top of their Miso after they tried this way. So, it's worth trying.


** If you have an access to Sake lees, it's also a handy ingredient to avoid molds on the top. I'll introduce how in the future.



② Raise Tamari on the top of your Miso to cover the surface.

Even if you can't place the weight all over the surface, Tamari also can help you. When tamari covers the top, it prevents Miso from non-necessary microorganisms. Please remember to use a deeper container for not to spill Tamari.  



That's all. Thank you for reading. If you try managing to make a suitable environment for your Miso, you can avoid being horrified by it.  



If you want to know more about how to remove yeast and mold from the surface, please check this page. There is also a short video about it.  

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