How Exactly Is Soy Sauce Made? (And Why It’s Basically a Delicious Science Experiment)

Soy sauce: the tiny bottle with the power to make your sushi sing, your stir-fry shine, and your dumplings dance. But have you ever actually wondered what’s going on in there? Spoiler: it’s not just salty brown magic. It’s a slow, carefully orchestrated fermentation party—and yes, there’s mold involved (the good kind).

Let’s take a saucy little stroll through how this umami bomb comes to life.

Step 1: The Fab Four (Plus Mold)

At its core, soy sauce is the result of four humble ingredients—soybeans, wheat, salt, and water—teamed up with a mold called Aspergillus (or, more commonly in Japanese production, koji mold).

Here’s the opening act:

• Soybeans are washed, soaked, and steamed until they’re ready to get cozy with the wheat.

• Wheat is roasted (which brings out a gentle sweetness) and crushed to make it extra friendly for fermentation.

• Brine—that’s salt and water—steps in to keep bad bacteria out and ensure that signature salty punch.

The soybeans and wheat meet the mold, mingle for about three days, then get a nice salty brine bath. At this point, they’re transferred to a tank and left to ferment for at least three months. This is where the magic happens: lactic acid forms, alcohol develops (yes, soy sauce naturally contains alcohol), and the umami deepens.

Step 2: Press, Rest, Heat, Bottle, Devour

When fermentation wraps, the mixture is pressed between cloths to create a smooth, flavorful liquid. This “raw” soy sauce chills out for a few days so sediment, oil, and sauce can separate. The prized middle layer—called clarified raw soy sauce—is heated to stop fermentation and stabilize flavor. Then, while it’s still hot, it’s bottled up and ready to make its way to your dumpling plate.

That’s the traditional method, which can take anywhere from three months to a year (or more). But supermarket shelves are also stocked with the “express” version—acid-hydrolyzed vegetable protein soy sauce—which skips the mold and gets from bean to bottle in about three days. Speedy, sure, but let’s just say your taste buds can tell the difference.

Soy Sauce’s Origin Story

Before soy sauce was soy sauce, ancient China had a thing for fermented protein-based sauces—often made from meat or fish. When Buddhism spread through China (and its vegetarian values took hold), soybeans stepped in to replace animal proteins. This gave birth to jiang (or jiangyou), a fermented soybean paste that’s basically soy sauce’s great-great-great-grandparent.

The first recorded Chinese recipe for jiang dates back to around 40 B.C. Fast-forward to 1228: a Buddhist monk named Kakushin visits China, learns how to make miso, and discovers that the liquid runoff from fermenting miso paste is a savory flavor goldmine. This happy accident becomes the earliest known soy sauce in Japan.

Over centuries, the method was refined, spawning multiple styles and categories—like koikuchi, tamari, shiro shoyu, usukuchi, and saishikomi—each with its own flavor personality.

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So next time you casually pour soy sauce over your sushi or whisk it into a marinade, remember: it’s not just a condiment. It’s a time-honored, mold-powered, months-long labor of love that’s been perfecting meals for over two thousand years.

And if you’re wondering which brand to grab from the grocery store? We’ll say it: Kikkoman reigns supreme for that balanced, everyday pour. Just don’t tell the artisanal small-batch soy sauce makers we said that.