Miso Development Diary

Miso Development Diary

We can buy miso easily at Japanese grocery stores or health food stores. But I heard that homemade one is really delicious and it’s also simple to make. So I gave it a try. I prepared ingredients for the fermentation process on January 17th. You can find a recipe from my recipe page.

The only difficult part is waiting. Miso has to be fermented just about 6 months to 1 year, depending on the season and other conditions. It also has to be checked and taken care of time to time. Remove mold, change top and bottom, and sometimes taste to see the progress.

Miso is ultimate slow food, which only can be developed by the aid of nature. This is a diary of my miso development.

Day 5


I already found white molds around the edge (see the red circled areas). I was using plastic wrap to seal to seal the surface, but obviously it wasn’t perfect.

I removed the molds, wiped the walls of the container with vodka, and sprinkled more vodka on the top surface to sanitize. Then, place new piece of plastic wrap on top to eliminate air contact.

I heard that white molds are normal in fermented food. They are not toxic, but change the flavor of miso. So it’s better to remove.


Day 42


Over a month has passed. When I took the container out of my closet, I noticed a small amount of dark liquid on top of miso. This dark liquid is called tamari (a type of shoyu).

I opened the lid, remove a bag of salt (weight), and a layer of plastic wrap to examine.

There were white molds around the corner of the container, but much less than the last time. I removed them carefully anyway. Probably vodka I sprinkled over the surface of miso worked well. I mixed the contents, in order to ensure the even fermentation; however, I probably didn’t need to do so, because the batch is very small.

But when I was turning, I noticed the consistency of miso was little softer. It might be something to do with vodka I sprinkled last time. Vodka prevents mold, but may increase water content. I heard that some miso makers use a type of washi (Japanese hand milled paper) to prevent molding and absorb extra liquid. I may try that. Also, color of miso gets darker as it develops. Compare the photo of day 5 and day 42.

While I was working on it, I couldn’t resist the wonderful fragrance. I decided to try a little. Just to make sure it’s going all right. I made miso soup with daikon and wakame. Oh… it was heavenly. I am not exaggerating. It was that good, even thought it wasn’t fully developed yet.

If I keep eating every time I examine, it would end up in a small quantity by the time it would be fully developed. I only used 1 lb of soy beans for this batch, but I probably should have needed 2 lb at least.


Day 75


I haven’t open the container over a month. As I heard that once tamari (dark liquid rising on top of miso) stars coming out, miso doesn’t develop mold any longer. Sure enough, I noticed that I didn’t find any mold.

It smells really like miso, and the color is darker. I didn’t see any blotchy dark and light spots, which I observed last time. I believe my miso is fermenting really nicely.

As usual, I dug a little and sampled some. Oh… it’s just sooooo good. I can’t believe miso could be so good by itself. Full of aroma and rich flavor packed with umami burst in my mouth. I cooked rice hastily to eat miso with rice, which is weird thing to do. But homemade miso was that good.

Then I wonder that whether it’s done. I know that it takes about 6 months for miso to develop. Mine is only 2-1/2 months old, but tastes good already. Early development may due to the warmer apartment temperature of NYC during winter. But this is the first time to make miso, and I really don’t know at what point miso is considered to be done.

My fried who makes miso time to time told me that there is no definite line between done and undone. It’s totally up to my taste buds and decision. He also mentioned that the miso won’t go bad, as koji is actively working to prevent spoilage. I decided to develop my miso even longer. I wonder how my miso changes by time.


Day 80


It’s less than 3 months, and it smells wonderful and taste fabulous. I could leave it to ferment for few months more, but I considered my miso is done.

It has been releasing large amount of tamari (dark soy sauce-like liquid, it can be used for flavoring food) from about a month ago. The miso started to get loose than it should be. As I learned that too much water content in miso can lead spoilage, I thought it may be the time to move it to the fridge.

I just run out of my white miso, anyway.

I am very curious about this early fermenting phenomenon. Regardless I make miso, Kinzanji miso, or sake, koji seems to ferment much quicker than in Japan. Maybe my apartment is warmer, which is possible because I live in a well heated apartment in New York. I wonder that it might have been a different story, if I kept my miso in a cellar (which I don’t have).

It means that whenever I try to make fermented food, I have to observe the development more carefully than people usually do in Japan.

If you have an experience of making miso in the U.S., I would love to know how did it go.

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2 Responses to Miso Development Diary

  1. Angel Heard-Fujimoto January 28, 2014 at 2:07 am #

    That mold scares me. Would that be ok to eat? Sucks, but maybe it’s better to start over and get a better seal.

    • Yuki January 28, 2014 at 10:02 am #

      I was wondering whether it’s ok to keep the batch after removing the molds. So I researched. The white mold is called sammaku-kobo (産膜酵母), which is necessary to make tsukemono pickles sour. Even though it is not toxic, it creates sour flavor. So that in the process of miso making, they have to be removed.