Miso making kit instruction manual
- kojikollective
- Oct 28, 2025
- 5 min read
Updated: Dec 23, 2025
What's in the kit
Koji salt mix
Dried soybeans
Resealable bag
Instructions
What you need
A large saucepan for boiling soybeans
A masher or tool for crushing soybeans (if using)
A large mixing bowl
Overview
Soak the soybeans
Boil the soybeans
Mash the boiled soybeans
Mix with salted koji
Pack into the bag and ferment
Preparation Steps
On the night before miso making
Rinse the soybeans thoroughly, rubbing them together, and change the water at least three times.
Soak the beans in at least three times their volume of water for 10–20 hours. (The soaking time may vary depending on the temperature. It takes less time when it's warmer. )
This allows the beans to absorb water all the way through.
On the day of miso making
The beans are ready when they have more than doubled in size, and the centre is evenly hydrated when split open, there should be no darker core remaining.
Drain, transfer the beans to the pot and fill with fresh water until the beans are just covered.
The cooking time depends on your chosen method of cooking.
In a saucepan on a hob: Bring to the boil, then simmer gently for about 3 hours. If the water level drops and the beans rise above the surface, add more water.
In a pressure cooker: Cook on "Beans" setting, or at high pressure for 10-12 minutes, then remove from heat and wait until the pressure releases naturally.
The beans are cooked when you can easily squash one into paste between your thumb and little finger (means very little effort!). If it's not soft enough, cook it for longer.
Drain and leave to cool until comfortable to touch.
Tip: The cooking water is full of goodness like vitamin B and antioxidant. It makes a lovely, mild stock for soups or noodles — don't throw it away!
Mash the soybeans into a smooth paste.
To do this, you can:
Place them in a thick plastic bag and mash by hand
Use a potato masher
Use a food processor
Use a meat mincer (manual or electric) — ideal if you plan to make miso regularly
Using clean hands, mix the mashed soybeans with the "koji salt mix" until the koji and salt are evenly distributed in the paste.
Shape the miso mixture into firm balls, pressing tightly to remove any air. This step is important to prevent air pockets, which can lead to mould growth.
To pack, press them firmly into the resealable bag, 1-2 balls at a time.
Remove as much air as possible before sealing the bag.
Label the bag with the date of preparation, and store upright in a cool, dark place.
As it ferments, some liquid may rise, so keep the bag standing.
It's natural for mould to appear on the surface of the miso. Check regularly and remove any mould that appears.
Miso made in winter will typically be ready by late summer (in 6-10 months time).
That's it!
Your homemade miso will slowly mature into a rich, complex flavour — the taste will deepen as the months pass.
Q&A, Trouble shooting
Can I use a container or jar instead of a plastic bag?
Of course you can!
After shaping the miso mixture balls, press them firmly to the bottom of the container so there are no gaps.
Don't fill the container all the way to the top since some liquid may rise. Leave at least 3 cm gap to the rim. For example, if you want to make 750 g of miso, you might want to use a 1-litre jar or larger.
Cover the surface with cling film. Put a weight (about 30 % of the miso's weight) on top. You can use a bag of salt or a pickle weight. And lastly, don't forget to label it.
How can you tell if the miso is ready?
As it matures, its colour changes from pale yellowish-brown to reddish-brown and finally to dark brown. During winter, its flavour evolves from light and delicate to rich and savoury, developing depth. If rice miso is left to mature for too long, it can become sour or develop a strong taste. Therefore, from late summer (eight months from preparation, when the miso turns reddish-brown) onwards, check its taste occasionally.
The miso is ready when you find it delicious when tasting a small amount from the centre or using one tablespoon of it in miso soup. Transfer it to the refrigerator or freezer to keep it at its best.
Although miso does not spoil, it continues to mature slowly even at low temperatures. It is recommended that you consume it within one to two years of completion.
Mould on miso
Miso will almost certainly develop mould (or mould-like growth) during the fermentation process.
White growth:
This is most likely kahm yeast, which forms when the surface is exposed to air.
It is harmless, but it can affect the flavour and promote moulds to grow on it. If found, remove approximately 5 mm from the surface.
Green growth:
This is most likely green mould. While it is not highly toxic, it should be dealt with promptly.
If found, remove the mould along with at least 1 cm of the surrounding miso.
The miso itself has turned dark:
This is most likely due to oxidation.
It is harmless, but the flavour may be affected. Remove the darkened portion before use.
Black growth on the surface of the miso:
This is most likely black mould.
If found, remove the mould immediately along with at least 1 cm of the surrounding miso.
Because mould cannot survive in environments with high salt content and little oxygen, miso may still be edible once the affected surface has been removed. However, consumption should always be based on your own judgement. If any part looks or smells unusual, it is best to remove it thoroughly, even if this means discarding more than expected.
Smell similar to natto / paste become sticky
If the miso develops a smell similar to natto (a strong fermented soy aroma, often described as pungent, earthy, or similar to strong cheese or ammonia) or/and become sticky and forms strings when pulled apart, there are several possible causes. These include whole soybeans remaining intact in the paste, uneven salt distribution in the paste, or cooked soybeans being left exposed for an extended period, allowing natto bacteria to take hold.
If there is no unusual taste, the miso is generally safe to eat. However, if you notice abnormal flavours such as bitterness or sharp unpleasant notes, unfortunately it should not be consumed. Miso that has become sticky and forms strings should also be avoided.
Natto bacteria (Bacillus subtilis) are not rare or exotic; they naturally exist in the environment and can be found on plants, in soil, and on everyday surfaces. For this reason, it is advisable to avoid eating natto on the day you prepare miso, but contamination could happen even if you don't eat it.
To help prevent this, avoid leaving cooked soybeans standing for extended periods, ensure that all beans are fully mashed, and mix thoroughly so that the salt and koji are evenly distributed.
We are working on translation!
茶色い水分が出てきた
熟成が進むと茶色い水分が上がってくることがあります。これは味噌たまりと呼ばれ熟成が順調なしるしです。少量であれば放置で大丈夫です。味噌の表面を水分が覆うことでカビ防止にもなります。あまりに多ければ味噌に混ぜ込むか、重しをしている場合は軽くしてみてください。幻の調味料とも呼ばれる味噌たまり、味噌が出来上がった際に残っていれば取り分けて醤油のように使えます。
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それでは美味しい手前味噌ライフを！