7 Steps to Making Soy Sauce for Sushi

Soy sauce is a popular condiment eaten with cultural dishes, including sushi. Traditionally prepared from fermented soybeans, grain, brine, and mold, this sauce has a robust and savory flavor, similar to broths. Homemade soy sauce takes six months to a year to complete, thanks to the long fermentation process.

To make soy sauce for sushi, soak soybeans for 24 hours. Cook them on high heat. Smash the beans to create a paste. Add ground, roasted wheat berries. Sprinkle kōji over the paste. Set aside in a warm area for two days. Make a brine and mix it with the kōji. After six months, strain into a bottle.

Sushi and soy sauce are a match made in heaven. Choosing a homemade sauce for your dish will elevate your sushi flavors. Read on for seven steps on how to make soy sauce for sushi.

Know Your Soy Sauce

Not all soy sauce is equal. Certain dishes taste best with specific sauces. For example, soy sauce for sushi is thin and mild. It complements the flavors of fish and rice, whereas Chinese soy sauce is usually chemically made, thick, and more robust in taste. Chinese soy sauce is typically used more in cooking, not for dipping sushi.

The best sauce for sushi, from sashimi to uramaki, is a traditional shoyu sauce. This Japanese soy sauce is made from soybeans, brine, wheat, and kōji (a mold—usually Aspergillus oryzae). Kōji is the key to starting the fermentation process. Shoyu sauce from scratch is a long process that requires much patience. 

Shoyu plays an essential role in sushi, and it’s the sauce that we’re used to seeing when we think of soy sauce. Creating homemade shoyu takes six months or more to make, but the result is worth it. You’ll end with a quality, authentic soy sauce that pairs well with sushi.

Gather Soybeans, Wheat Berries, & More

To make Shoyu, you’ll need water, salt, soybeans, wheat flour or wheat berries, a kōji starter, and lots of time. Creating homemade soy sauce is not a short process. If you’re looking for a quick, simple soy sauce recipe for sushi, there’s one at the end of this post that implements store-bought soy sauce. 

Here’s what you’ll need to make traditional shoyu sauce:

Ingredients

  • 2 ½ lbs mature soybeans (light-colored, not green)
  • 2 ½ lbs wheat berries
  • ¼ oz Aspergillus oryzae starter
  • 1 ½ lbs sea salt
  • 1 gallon filtered water

Equipment

  • Coriander
  • Mason jar (gallon-sized)
  • Pressure cooker with a steamer basket
  • Large mixing bowl
  • Food processor
  • Parchment paper
  • Stainless steel baking sheets (2)
  • Pressure cooker
  • Food thermometer
  • Plastic wrap
  • Two-gallon container with lid
  • Glass bottle
  • Cheesecloth
  • Strainer
  • Funnel

Soak the Soybeans for 24 Hours, Cook, & Smash Them

Soybeans are legumes, and these legumes are native to Asia, where they’re grown for multiple purposes and used to create various foods, from soy milk to tempeh. The beans are also eaten directly from their pods as edamame. Soybeans contain all amino acids, so they’re considered a complete protein.

Here’s how to prepare your soybeans for your soy sauce:

  1. Weigh out your soybeans. Rinse them well in coriander.
  1. Transfer the clean soybeans to a gallon-sized mason jar. Add filtered water to the jar until the soybeans are just covered.
  1. Soak the soybeans for 24 hours. The beans will expand as they absorb water, so top off the water as needed to ensure proper hydration. Don’t let the beans dry out.
  1. Drain the soybeans after 24 hours.
  2. Transfer to a pressure cooker steamer basket. Add a cup of water to the pressure cooker and attach the steamer basket.
  1. Cook the beans on high for an hour and a half up to two hours. 
  1. Smash the soybeans with a potato masher to create a paste. Set aside.

Broil Wheat Berries & Grind in a Food Processor

All wheat products start as simple wheat berries, including flour. Some soy sauce recipes call for the use of wheat flour, but wheat berries are a better idea for the sake of authenticity. There are different wheat berries, but the best for soy sauce is the soft red and white varieties.

Here’s how to prepare your wheat berries:

  1. Weigh out your wheat berries with a food scale.
  1. Place the berries on a baking sheet lined with parchment paper.
  1. Broil them in the oven until golden brown. Check them every minute and stir to prevent burning.
  1. Remove from the oven and cool once they’ve reached the desired color.
  1. Transfer the roasted wheat berries to a food processor.
  1. Grind the berries until they’re a coarse powder.

Once you have your wheat berry powder, combine it with the soybean paste. Mix until well incorporated.

Start Fermentation With Aspergillus Oryzae & Kōji

Traditional soy sauce is made through one of two methods: fermentation or chemical-hydrolyzation. Chinese soy sauces are typically made via the chemical-hydrolyzation process. On the other hand, around 85 percent of soy sauce in Japan is created via the fermentation method. For authenticity, we’ll stick to the fermentation method in these steps.

Here’s how to begin the fermentation process:

  1. Weigh out the Aspergillus oryzae. 
  1. Sprinkle it into the soybean paste/wheat berry mixture. Mix well.
  1. Spread the paste over two stainless steel trays. The paste should be about two inches thick.
  1. Separate the paste into three-inch blocks, keeping them about two inches apart. As the kōji starts the fermentation process, it generates heat. Keeping the blocks apart prevents the paste from thickening too much as it heats up.
  1. Add a food thermometer to the tray. Cover the tray tightly with plastic wrap.
  1. Keep the wrapped tray around 85 degrees Fahrenheit (32 degrees Celsius). Monitor the temperature for the next two days. Remember that once fermentation begins, the paste will start to smell, so keep it in an area that won’t bother you or your family.
  1. Check the blocks after two days. They’ll have a white, fuzzy layer of mold over them.
  1. Cut away and toss out any dark green, black, sticky, or shiny pieces. Light green and yellow bits are fine.

Make the Brine Solution & Mix It Once a Week

Soy sauce is up to 18 percent salt. While microbial life is a significant part of soy sauce production, salt helps to inhibit certain microbes selectively once the fermentation process begins.

After your kōji blocks have sat for two days, start preparing your brine. Here’s how:

  1. Mix a gallon of filtered water with 1 ½ lb of sea salt in a large container with a lid. Stir until dissolved.
  1. Add the kōji blocks into the salt water and stir. 
  1. Cover the mixture with a tight-fitting lid. 
  1. Place the container in a warm area of your home. That way, it can continue the fermentation process.
  1. Stir daily for the first week and once a week for the months following. Let the mixture sit for six months to a year.

The longer the mixture sits, the more rich its flavor will be. For a darker shoyu, you can place the mixture in the sun during the warmer months.

Strain Your Shoyu After Six Months

After six months to a year, the kōji fermentation process will be complete. You may then strain the mixture to obtain your soy sauce.

The sauce should be a brown, transparent liquid when stored indoors. If allowed to ferment in the sun, the sauce will be a darker brown and more opaque.

  1. Line a large strainer with a cheesecloth. 
  2. Strain the mixture over a large bowl, twisting the cloth to get all the remaining liquid. 
  3. Pour the bowl of liquid into a funnel over a soy sauce jar. 
  4. Add a tight-fitting lid. 
  5. Store your soy sauce in the refrigerator until you’re ready to use it.

A Quick Soy Sauce Recipe for Sushi

Homemade soy sauce takes time and patience to make. However, there are quick, easy soy sauce recipes that you can use in the meantime. The recipe below implements store-bought soy sauce, so it’s not truly “made from scratch.” However, it’s an excellent alternative until your shoyu finishes fermenting.

Here are the ingredients:

  • 4 tbsp store-bought soy sauce (reduced sodium)
  • 2 tsp sesame oil
  • 2 tsp rice vinegar
  • 2 tbsp mirin (more for extra sweetness)
  • 2 tbsp lemon juice (freshly squeezed)

Combine all ingredients in a small bowl, funnel into a glass jar, and serve with your favorite sushi. Store in the refrigerator to use for another time.

Conclusion

Anyone can visit a grocery store and pick up a bottle of commercial soy sauce. It’s easy and convenient, but these chemical-laden sauces will never compare to a homemade sauce. When it comes to creating a soy sauce for sushi, patience is an absolute must. The six-month fermentation process results in a savory, authentic sauce with an unmatched flavor that pairs beautifully with sushi.

Here are some of my favorite sushi making tools

Thank you for reading this article. I hope you find it useful as you make sushi at home. Here are some tools I’ve used that I hope you’ll find helpful, too. These are affiliate links, so if you decide to use any of them, I will earn a commission. But honestly, these are the exact tools that I use and recommend to everyone, even my family.

Rice cooker: For getting started, I really like Zojirushi Rice Cooker. The Zojirushi Rice cooker does not only make rice-cooking dirt simple, but it is a quality gadget that cooks better than most chefs can. Unlike most kitchen gadgets, it does not sacrifice quality for convenience.

Knife:The Kai Knife is one of the best sushi knives in the market. Made in Japan’s famous knife-making capital, Seki city.

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