• Soak beans in 3 times the weight of filtered water overnight (up to 24 hours).
• Drain beans from soaking liquid.
• Bring 1/2 gallon (2 liters) of filtered water to a boil, then add beans and reduce heat to simmer. Cook until soft (cooking time varies by bean).
• Drain beans over a colander placed over a heat-proof container to capture the cooking liquid. Add beans to a large mixing bowl.
• If using dried koji, dissolve 160 g salt in 400 ml of the cooking liquid you reserved. If using fresh koji, dissolve 80 g salt into 200 ml cooking liquid. Let brine mixture cool down to 100°F/38°C.
• Mash the beans, leaving about 1/4 of them intact.
• Add mature miso to the beans. Stir until it is incorporated.
• Once bean mixture has cooled down down to 100°F/38°C, add the warm brine and then stir in koji. Mix well for a few minutes. The koji will absorb much of the cooking liquid.
• You should be able to form balls with the mixture that stick together. If they crumble in your hand, add more of the cooking liquid.
• Sprinkle water on the inside walls of the fermenting jar/vessel, then quickly add sea salt to the bottom and sides so it sticks to the inside of the jar.
• Pack the vessel with the mixture, ensuring there are no air bubbles in the jar.
• Once packed, tap vessel on a towel or wooden cutting board several times to ensure that any air bubbles in the mixture come to the surface.
• Add remaining salt to the top layer of the mixture.
• Add a weight to the top of the mixture. This will weigh it down and allow the tamari to rise to the surface during fermentation.
• If using, wrap the top of the vessel in a cloth or canvas swatch, and tightly secure it with a rubber band, bungee cord, or tape). Or place the vessel into a paper or canvas/cloth bag. Staple and/or tape it shut so no insects can enter.
• Write the starting date on the bag or affix a label to the side of your vessel. Set a calendar appointment for the next cool season to check your miso!
• Store it in an unheated space for at least six months (until next cool season), and over one summer. You can ferment as long as 24 months.

Post-Fermentation (6 months to 1 Year Later)

• Carefully open the bag and remove the vessel.
• Remove the weight. Scoop off any funky mold from the top surface.
• Blend into a smooth paste using a food processor or powerful blender. Add a small amount of filtered water if mixture is too thick to blend.
• Pack contents into a glass jar. If using a metal lid, store with a layer of parchment paper between the metal lid and the lip of the jar.
• Store in the refrigerator. Lasts several years there.