Homemade Fermented Soy Sauce — Traditional Recipe

Homemade fermented soy sauce in a glass jar — Homemade fermented soy sauce

Homemade fermented soy sauce is made by cooking soaked soybeans, mixing them with toasted wheat flour and koji starter (Aspergillus oryzae), letting the mixture grow mold for 48 hours in a warm place, then fermenting it in salt brine for 6 months before straining and aging the liquid for one more month. It takes 30 minutes of active work and about 7 months in total, and makes about 1 liter.

An ancient condiment of Asian cooking with an intense umami flavor, here in a simplified home version that respects the basic principles.

How to Make Fermented Soy Sauce?

Soy sauce is made by fermenting soybeans, toasted wheat, salt, and water with a koji starter in a process that takes at least 6 months.

Nutritional Information

Each 15 ml serving of fermented soy sauce contains approximately 10 kcal, 1 g of protein, 0 g of fat, 0 mg of cholesterol, 1 g of carbohydrates, 0 g of sugars, and 900 mg of sodium. These values are estimates and may vary depending on ingredients and portion sizes.

Homemade Fermented Soy Sauce Recipe

Preparation: 30 minutes (plus 6 months fermenting)
Cooking: 2 hours
Servings: 60 servings of 15 ml (1 liter)

Ingredients

500 g of dried soybeans
500 g of wheat flour
3 liters of filtered water
250 g of salt
1 tablespoon of koji starter

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Instructions

Soak the soybeans in water for 12 hours, then cook over medium heat for 2 hours until soft. In a dry skillet, toast the flour until lightly golden. Let the soybeans cool and mix them with the toasted flour and the koji.

Dried soybeans for homemade fermented soy sauce — Soybeans

Spread the mixture on a tray and cover with a damp cloth. Leave it in a warm place (25 to 30°C, 77 to 86°F) for 48 hours until a white mold appears. Dissolve the salt in 2 liters of filtered water, place the fermented mixture in a large jar, and cover it with the brine.

Koji starter for fermented soy sauce — Koji Starter

Ferment for 6 months, stirring occasionally and keeping the mixture covered with liquid. Then strain the liquid and age it in an airtight jar for one more month before using.

Additional Tips

Avoid chlorinated water

Chlorine inhibits the koji microorganisms, so use filtered or boiled and cooled water.

Skip metal tools

Use wood, glass, or plastic to stir and handle the mixture, since prolonged contact with metal can affect flavor and fermentation.

Keep it submerged

The solids must always stay under the brine to avoid unwanted mold.

Original ingredient	Substitute	Ratio	Flavor note
Wheat flour	Cracked toasted wheat	500 g	More traditional
Fine salt	Sea salt without additives	250 g	Cleaner flavor
6 months	12 months	Longer aging	Deeper flavor
Homemade	Store bought low sodium soy sauce	To taste	Instant

Frequently Asked Questions (FAQs)

1. What is koji?

Koji is rice or grain inoculated with the mold Aspergillus oryzae, the starter used to ferment soy sauce, miso, and sake.

2. Why does it take so long?

The slow fermentation breaks down soy and wheat proteins and starches into the amino acids and sugars that give soy sauce its umami flavor.

3. How do I store homemade soy sauce?

In a clean, airtight glass bottle in a cool place or the fridge once it has aged.

History of Soy Sauce

Soy sauce originated in China more than 2,500 years ago as a way to stretch salt. Its fermentation technique was refined during the Tang dynasty (618 to 907 AD) and spread to Japan and Korea, where varieties such as shoyu and tamari developed.