Koji & Miso

How to make Miso

A savoury fermented paste of soybeans, rice koji, and salt, aged slowly into deep umami. Plan on an overnight soak and a few hours of cooking and mixing, then 6-12 months of patient fermentation, tasting from around six months to decide when it is ready.

Quick answer

Sort and rinse the soybeans, then soak them overnight so they cook evenly. After 1 day, cook the soybeans until very soft, reserve some cooking liquid, then mash and cool them. After 1 day, mix the koji and salt into the cooled beans, then pack the paste tightly into the crock. After 90 days, check the surface, skim any growth, and press the miso back down before it keeps ageing. After 180 days, taste the miso and decide whether to use it now or let it age deeper, then refrigerate.

Difficulty
Intermediate
Total time
180 days
Ingredients
3
Steps
5

Safety

  • • Use the full measured salt. It is the main control that keeps miso safe through months of fermentation.
  • • Let the cooked beans cool to lukewarm before adding the koji, as heat kills the culture.
  • • Pack out air pockets and keep the surface capped with salt and a pressed cover.
  • • Surface mold on long ferments is usually skimmed off and the paste beneath is fine. Discard only if the whole batch smells putrid or mold runs deep throughout.

Step-by-step

Day 0

Step 1: Soak soybeans

Sort and rinse the soybeans, then soak them overnight so they cook evenly.

  • Set up clean equipment Wash the pot, bowls, masher, crock, and weight before you start.
  • Sort and rinse beans Pick out any damaged beans or debris, then rinse the soybeans well.
  • Soak overnight Cover the beans with plenty of cold water and soak for 8-12 hours.
Day 1

Step 2: Cook and mash

Cook the soybeans until very soft, reserve some cooking liquid, then mash and cool them.

  • Cook soybeans Simmer the drained beans until a bean crushes easily between two fingers.
  • Reserve liquid and drain Save a cup of the cooking liquid, then drain the beans.
  • Mash beans Mash the warm beans into a rough, mostly smooth paste.
  • Cool to lukewarm Let the mashed beans cool to body temperature before they meet the koji.
Day 1

Step 3: Mix and pack

Mix the koji and salt into the cooled beans, then pack the paste tightly into the crock.

  • Mix koji and salt Combine the koji with most of the salt, keeping a spoonful of salt back for the top.
  • Combine into paste Mix the koji and beans together, adding reserved liquid until the paste holds together.
  • Pack the crock Press the paste into the crock in layers, removing every air pocket.
  • Salt and seal the top Cap the surface with the reserved salt, press a cover onto it, and weight it down.
Day 90

Step 4: Check fermentation

Check the surface, skim any growth, and press the miso back down before it keeps ageing.

  • Check the surface Lift the cover and look at the top of the miso and any liquid that has gathered.
  • Skim and press down Scrape off any surface mold, press the miso flat, and re-cap it.
  • Check aroma The miso should smell increasingly savoury, sweet, and mellow.
Day 180

Step 5: Taste and store

Taste the miso and decide whether to use it now or let it age deeper, then refrigerate.

  • Taste miso Take a small taste and judge the colour, saltiness, and depth of flavour.
  • Transfer and refrigerate Pack the finished miso into clean jars and refrigerate to slow the fermentation.

What to look for

  • • After packing: The paste is packed down firmly with no air pockets, capped with salt and a pressed cover. A tight, airless surface is what keeps the long ferment clean.
  • • Around 3 months: The colour is deepening, the smell is savoury and sweet, and tamari may pool on top. These are signs of a healthy ferment. Skim any surface growth and press the miso back down.
  • • 6-12 months: A taste from within the paste is deeply savoury and rounded, with the salt mellowed into umami. That is the point to use it or keep ageing for a darker, stronger miso.

Troubleshooting

  • Mold or a film grows on the surface. Air reached the surface through a gap or a loose cover. Scrape it off generously with a thin layer of miso beneath, press the rest down, re-salt, and press the cover back onto the surface.
  • Dark liquid pools on top. This is tamari, a normal by-product of the ferment. Stir it back in for a moister miso, or spoon it off and use it as a rich seasoning.
  • The paste is dry and crumbly when mixing. Not enough cooking liquid was worked in. Add the reserved cooking liquid a little at a time until the paste holds together when squeezed.
  • Gritty white specks appear in the aged miso. Harmless tyrosine crystals from the amino acids in the paste. Nothing is wrong. They are safe to eat and a sign of a well-aged miso.

Storage

Once the colour and flavour are where you want them, pack the miso into clean jars, press out air, smooth and lightly salt the top, seal, and refrigerate to slow the fermentation.

Shelf life: a year or more refrigerated

Serving suggestions

  • • Whisk a spoonful into hot (not boiling) water with greens for a quick soup.
  • • Use it in marinades and glazes for vegetables, fish, or tofu.
  • • Stir it into dressings, dips, and braises for savoury depth.

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Frequently asked questions

What is Miso?

A savoury fermented paste of soybeans, rice koji, and salt, aged slowly into deep umami. Plan on an overnight soak and a few hours of cooking and mixing, then 6-12 months of patient fermentation, tasting from around six months to decide when it is ready.

How long does it take to make Miso?

Most batches of Miso are ready in about 180 days, though exact timing depends on temperature and how the ferment tastes along the way.

Is Miso hard to make?

Miso is an intermediate project — straightforward for home fermenters with a bit of experience.

What do you need to make Miso?

You'll need Dried soybeans, Rice koji, Sea salt.

How do I know when Miso is ready?

Watch for these cues: After packing: The paste is packed down firmly with no air pockets, capped with salt and a pressed cover.; Around 3 months: The colour is deepening, the smell is savoury and sweet, and tamari may pool on top.; 6-12 months: A taste from within the paste is deeply savoury and rounded, with the salt mellowed into umami..

How do I store Miso?

Once the colour and flavour are where you want them, pack the miso into clean jars, press out air, smooth and lightly salt the top, seal, and refrigerate to slow the fermentation. Shelf life: a year or more refrigerated.

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