preserve · Preserve

How to Make Miso Paste at Home

Making miso paste requires fermenting cooked soybeans with koji (rice inoculated with Aspergillus oryzae) and salt for 6 months to 3 years. You'll need precise ratios, sterile conditions, and patience. The process involves mashing beans, mixing with koji and salt, packing into containers, and aging in a cool, dark place while monitoring for proper fermentation.

Total time: 6 months
Hands-on: 2 hr
Difficulty: Hard

Ingredients

2 pounds dried soybeans
1 pound koji rice
8 ounces sea salt

Step by step

Prepare the soybeans. Soak 2 pounds dried soybeans in water for 12-24 hours until they double in size. Drain and boil for 3-4 hours until you can easily mash them between your fingers. Reserve 2 cups of the cooking liquid before draining.
Mash the beans. Let beans cool to room temperature. Mash thoroughly using a potato masher, food processor, or meat grinder until you have a smooth paste with no whole beans remaining. The consistency should be like chunky peanut butter.
Mix with koji and salt. Combine 1 pound koji rice with 8 ounces sea salt in a large bowl. Add the mashed soybeans and mix thoroughly with clean hands. Add reserved cooking liquid gradually until the mixture holds together when squeezed but isn't wet.
Pack into containers. Form the mixture into softball-sized balls and press firmly into clean glass jars or food-grade plastic containers, eliminating air pockets. Press a layer of plastic wrap directly onto the surface, then cover with cheesecloth.
Begin fermentation. Place containers in a cool, dark spot around 60-75°F. Weight down the surface with clean stones or a plate. The miso will develop a layer of liquid on top - this is normal. Stir once every few months and taste after 6 months.
Age to taste. Continue aging 6 months to 3 years, tasting periodically. Young miso tastes sweet and light. Mature miso develops deep, complex flavors. When you like the taste, refrigerate to slow fermentation.

Tips & troubleshooting

Buy koji from a reputable supplier and use it fresh - old koji won't ferment properly
Use only non-chlorinated water throughout the process as chlorine kills beneficial microorganisms
Sterilize all equipment with boiling water before use to prevent unwanted bacteria
The white bloom that appears on top is kahm yeast - scrape it off but don't worry if some remains
Taste monthly after the first 6 months to track flavor development
Save a small amount of finished miso to inoculate your next batch for faster fermentation

Variations

Red Miso. Use more salt and age for 2-3 years for a darker, more intense flavor. The longer aging develops the characteristic red-brown color.
White Miso. Use more koji, less salt, and age only 6-12 months. This creates a sweeter, lighter-colored miso perfect for delicate dishes.
Mixed Bean Miso. Replace half the soybeans with chickpeas, black beans, or adzuki beans for unique flavors and colors.
Barley Miso. Substitute barley koji for rice koji to create a nuttier, earthier miso with different fermentation characteristics.

Questions

Where can I buy koji for making miso?: Order koji online from specialty suppliers, Japanese grocery stores, or shops that sell fermentation supplies. Some health food stores carry it in the refrigerated section. Fresh koji works better than dried.
How do I know if my miso has gone bad during fermentation?: Good miso develops white or light-colored surface mold and smells earthy and fermented. Bad miso has black, green, or fuzzy mold, smells rotten or overly sour, or develops an off-putting chemical smell.
Can I speed up the fermentation process?: Warmer temperatures speed fermentation but can create off-flavors. Keep it around 70-75°F maximum. You can also add a small amount of finished miso to inoculate the batch, which can reduce aging time by several months.
Why is my homemade miso too salty?: You used too much salt in the initial mixture, or the fermentation hasn't progressed enough to develop complex flavors that balance the salt. Give it more time, or next batch use slightly less salt.
What's the difference between using different types of koji?: Rice koji creates classic, well-balanced miso. Barley koji produces nuttier, earthier flavors. Soybean koji makes pure soybean miso with intense umami. Each ferments at slightly different rates and develops unique flavor profiles.