A brief introduction to soy sauce, a key flavoring ingredient in Chinese cooking.

What are the ingredients in soy sauce?

Soy sauce is a dark-colored, concentrated liquid made by fermenting soybeans and wheat. Good soy sauce has an intense, mouth-filling saltiness and a wonderful aroma that’s toasty and slightly fruity.

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Soy sauce was initially the liquid residue of fermenting soybeans for soybean paste (豆酱 dòujiàng), which has been produced in China since 200 CE. The byproduct was called 酱油 jiàng yóu (“soybean paste’s oil”). By 1000 CE, this liquid condiment was more popular than soybean paste, and produced and enjoyed for its versatile use in cooking.

To make soy sauce, the craftsmen soak yellow soybeans until plump, then steam them for a few hours until soft. They crush the beans coarsely and leave them to ferment in a warm place for 3 days until a yellow-green Aspergillus mold develops. At this point, roasted and crushed wheat is usually added to the mixture. The craftsmen then place the hot, ripe-smelling soybeans and wheat into crocks or barrels, alternating the layers with a brine of salt and water. They cover and leave the mixture to ferment for several months.

In their crocks, the enzymes break down the soy proteins into amino acids and the soybean oil into fatty acids, producing sugars, alcohol, roasty and fruity-smelling pyrazines and esters, and meaty sulfuric compounds. Sometimes, a sugar syrup is added during the final fermentation to develop more flavors. The final liquid is salty, sweet, tart, and savory, loaded with umami-tasting glutamic acids.

In dishes, soy sauce adds saltiness but also intense flavor.

Difference between Japanese and Chinese soy sauce

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In a typical Asian supermarket you’ll find two main kinds of soy sauce: Japanese and Chinese.

Japanese soy sauce (shoyu) is made with a nearly equal blend of soybeans and wheat— the starch in the wheat adds a characteristic sweetness and rounder flavor, and a higher alcohol content and alcohol-derived aromas.

Chinese soy sauce (jiangyou) is primarily made of soybeans, and it’s darker in color and saltier in flavor than Japanese soy sauce and not as sweet. Most Western grocery stores only carry Japanese soy sauce, like Kikkoman’s, but for Chinese cooking, I recommend seeking out a Chinese soy sauce, as it has a different flavor profile.

How do I identify naturally brewed soy sauce?

To see if the soy sauce is naturally brewed from soybeans, look at the label: the ingedients should be water, soybeans, wheat, sugar, and alcohol— hydrolyzed protein or caramel color is a dead giveaway of non-fermented, “fake” soy sauce. It’s made with chemically modified soy protein, and colored and flavored with corn syrup and caramel to approximate the look and taste of real soy sauce.

Good soy sauces can range widely in flavor, like any good wine or vinegar, with different notes of earthy, fruity, or nutty aromas.

I always look for an organic soy sauce. The enduring favorite in my kitchen is Wan Ja Shan (萬家香) organic soy sauce. Kimlan (金蘭) soy sauce is also a good one. As with any Chinese condiment, I usually go with the Taiwanese brands, which are better in quality.

Avoid low-sodium soy sauce. They’re usually inferior in flavor and aroma, and you can easily control the amount of sodium in a dish yourself by using smaller amounts of soy sauce or by using less salt.

You can buy soy sauce online, but it’s much cheaper to purchase in your local Asian supermarket.

Difference between light and dark soy sauce

Light and dark soy sauce are Cantonese soy sauces. Because these two kinds of soy sauce were popularized by Cantonese cooking in China and America, they are now considered standard.

Light/regular soy sauce (生抽, shēngchōu) is all-purpose: it’s light in color, thin, and salty. Light refers to the color— it’s not lighter in sodium, and actually saltier than dark soy sauce.

Dark soy sauce (老抽, lǎochōu) has sweet, caramel tones, and it’s thicker and richer in flavor, but less salty. It’s used sparingly to add color to dishes, particularly braises.

Most Cantonese brands like Pearl River Bridge (珠江桥牌) will come in light and dark soy sauces, but other brands just offer one general “soy sauce,” which is equivalent to light soy sauce. Outside of southern cooking, other regions in China don’t really call for these two distinct types of soy sauce and you’ll be good with just a bottle of regular soy sauce in most recipes.

Is soy sauce gluten-free?

Most brands of soy sauce contain wheat. For a gluten-free soy sauce, look for tamari. This is a kind of Japanese soy sauce closest to the Chinese original, made from fermented cooked soy beans without the addition of wheat. It has a bolder, richer flavor because of the higher concentration of soybean amino acids, and can be used in place of regular light soy sauce.

How to store soy sauce

Soy sauce lasts almost indefinitely, but the flavors can dissipate after a few months. Store the bottle tightly capped on the counter away from the stove, or in a cool, dark cupboard. Some chefs refrigerate their best soy sauces to preserve their flavor and freshness.