Miso is a traditional Japanese condiment of fermented beans (soybeans, adzuki beans, chickpeas) and optionally grains (barley, rice, millet, wheat), with salt and the fungus koji. Beans are cooked, crushed and mixed with koji and salt, then placed in a container to ferment. Gradually, a umami-rich, amber liquid called tamari rises to the surface as powerful enzymes supplied by koji, along with fermenting organisms from the environment, break down complex compounds in the beans into readily digestible amino acids, fatty acids and simple sugars. Unpasteurised miso contains live enzymes and many trace minerals. Miso is typically used as a flavouring to season soups and dishes, and to tenderise and preserve foods. You can read more on miso and miso varieties in this post.
Cook the beans
Soak the beans in plenty of water for at least 12 hours. Drain, then cook the beans in one of the following ways:
- Pressure cooker. Pressure cook the beans in a pressure cooker for 10-15 minutes.
- Stove. Simmer the beans gently over low heat until tender, about 2-4 hours, depending on the type of bean.
Test for doneness by squeezing a bean between your fingers; it should give way to pressure. Drain the beans and save some of the bean cooking liquid for rehydrating dried koji.
Rehydrate the Koji
Outside of Japan, most koji is sold in dried form so I will write the instructions for preparation of salted koji for miso from dried koji. Rehydrate dried koji in warm water or reserved bean cooking liquid that has been cooled to 60°C (140°F). Add about a tablespoon at a time, letting the liquid absorb for a few minutes before adding another tablespoon. The koji should be just hydrated; not wet. Allow at least 30 minutes for the moisture to penetrate the koji grains. Once it is the right consistency, weigh the koji.
The proportion of koji, beans, and salt is one of the many factors that determine the personality and fermentation period of miso. The more koji, the sweeter the miso. The lesser the salt, the faster the fermentation and lighter the taste – think sweet white or Saikyo miso. As a general guide, for 454g (1 lb) beans and 227g (1/2 lb) salt, the higher limit of koji is 1.5x or 680g (1.5 lb), and the lower limit of koji is 0.75x or 340g (0.75 lb).
The table below summarises the ratios of koji, bean, and salt, and fermentation time for different varieties of miso.
Combine and Mash the Miso Ingredients
Mash the beans, koji and salt together while they are still warm; it becomes difficult to crush cooled beans. Allow the cooked beans the cool off until it reaches 60°C (140°F).
Mashing of the ingredients can be done in a few ways depending on the type of beans, quantity prepared, and desired texture. A food processor is helpful for processing harder beans such as soybeans and chickpeas, or if preparing a large batch of miso. A mashing rod or rolling pin and ziploc bag, or potato masher will suffice for softer beans, or if preparing a small batch of miso, or if a chunkier texture is preferred in the final miso.
If the mixture gets too thick, add a little of the bean cooking liquid. A dough-like consistency will yield a paste-like miso, whereas a chunky texture will yield a country-style miso. Which style you choose depends on your preference. Add the seed miso (if using), and mix again until everything is evenly blended.
Prepare Container for Miso Fermentation and Packing
The container for miso should be 1.5 times in volume of the miso to be made. The sidewall of the container must be vertical to allow the droplid to fit regardless of the amount of miso inside. The container may be made of glass, ceramic, or plastic. Do not use any metal container even it is stainless steel; stainless steel may be corroded although rust may not be visible to the naked eye. Wash the container carefully, and dry completely.
Sprinkle salt evenly over the inside of the vessel.
Pack the miso into the vessel, a spoonful at a time, tamping as you go to remove any air pockets. Smooth out the top surface of the mash. Cut a piece of muslin to fit perfectly across the top of the miso. Sprinkle salt along the edges of this cover to seal any gaps.
Drop lids & weights
Weights are essential for making miso. If miso is made without weight, a harsh and sour product with strong smell of esters will result. A suggested total weight is at least 60% of the miso being fermented (best is equal weight). There are special fermentation weights available, or you could use a ziploc bag filled with grains or salt. Cover the container with a lid.
Ageing and Turning over
Place the miso vessel at room temperature on the countertop, or somewhere accessible, for the first few weeks, so you can easily check and ensure proper fermentation before moving it to its permanent home.
After a few weeks to one month, you should see a brown liquid (tamari) pooling on top. This is an indication of the fermentation going well, and you can now set aside the miso for months. If you do not see tamari, add more weight and check again after a few weeks.
Some tamari can be strained off for consumption, but the rest should be stirred back into the miso. The miso mixture must be mixed so the bottom and top are turned over. The purpose is to expel the gas generated during the ageing process, and to expose to fresh air briefly. When finished, repack just as the initial packing.
If any mold is found on the surface, remove it carefully.
Taste-Check Along the Way
You can taste-check your miso during the fermentation process. Carefully lift the weights and set them on a clean surface. Insert a long spoon or butter knife into the miso and pull out a small amount that is deeper; it will give you a better sense of the miso than the product that is on the surface.
When assessing if the miso is ready, consider three factors – colour, aroma, and taste. The colour should take on the intended due – light beige, yellow, or russet – depending on the intended miso type. The aroma should be slightly alcoholic and yeasty, but pleasant smelling. A strong alcoholic smell usually indicates the mixture has overheated and needs to ferment more. In this case, allow the mixture to ferment longer in a cooler environment. In mature miso, the initial harsh, salty taste of unfermented miso should be mellowed, and a subtle sweetness should be apparent, particularly with short-term varieties. If the miso is too salty or too light, ferment it a little longer.
After you have tasted, smooth the surface, sprinkle salt, and tuck the muslin and weight as before.
Store finished miso
Once you are satisfied with your miso, the finished miso can be stored directly, or blended in a food processor for a smoother texture. Store the final miso in an airtight container in the refrigerator, where it will be stable. Ideally, sweet miso should be consumed within 9 months, and dark miso within 18 months. After this time, the miso can still be used, but its overall taste and quality will be sub-optimal.
For More on Miso and Koji Fermentation, check out my:
General overview of miso (glossary entry)
Koji Applications – The Fun-Guys of Japanese Fermentation
Cooking with miso – Miso Soymilk Paitan Rawmen
Cooking with miso – Yasai no Shirae (Vegetables in White Dressing)
Cooking with miso – Miso-cured Tofu