Published January 1, 2007. From Cook's Illustrated.
This Asian condiment should enhance flavor and contribute complexity to your food—not just make it salty.
Most of us have rarely given soy sauce a second thought, using it as a kind of liquid salt. But this 2,500-year-old ingredient, brewed first in China and since the seventh century in Japan, can offer nearly as much variety, complexity, and flavor as wine or olive oil, and it deserves serious consideration. In most supermarkets today, you will find a shelf of imported soy sauces, as well as American-brewed versions. How do they differ?
We decided to sample nationally available brands, choosing a lineup of 12 soy sauces, including both tamari and regular soy sauce, from Japan, China, and the United States. We tasted them three times: first plain, then with warm rice, and finally cooked in a teriyaki sauce with ginger, garlic, and mirin and brushed over broiled chicken thighs. As we tasted them, we noticed a wide range of colors and flavors, from reddish-brown, delicate, and floral to dark brown, pungent, and assertive. Where were these differences coming from? And how well did they play off the other flavors in a dish?
At its most basic, soy sauce is a fermented liquid made from soybeans and wheat. Soybeans contribute a strong, pungent taste, while wheat lends sweetness. Tamari is a type of soy sauce traditionally made with all soybeans and no wheat—though, confusingly, many tamaris do contain a little wheat. As a result, tamari has a more pungent flavor than soy sauce. Similarly, stronger, earthier Chinese soy sauce tends to be made with a lower proportion of wheat than the sweeter, lighter Japanese soy sauce.
Like many products with a long history, soy sauce is now made both artisanally using traditional methods and industrially using modern technology. All soy sauce begins with whole soybeans or defatted soy meal cooked and mixed with roasted grain, usually wheat (but sometimes barley or rice). This bean/grain mixture is inoculated with a mold called koji (technically, Aspergillus oryzae or Aspergillus soyae) and left for a few days to allow the mold to grow and spread. Then salt water and yeast are added to form a mash called moromi. And here comes the biggest difference in quality levels of soy sauce: The mash is fermented for anywhere from two days to four years. The brown liquid that is extruded from the mash is soy sauce, which is usually filtered, pasteurized, and bottled.
Experts claim that each soy sauce gets its particular flavor from the proportion and quality of the ingredients, including the local water where it's brewed, the koji "starter" mold (some companies brag of their proprietary koji, kept alive for centuries), the climate (a certain level of humidity is essential to make the mold grow), and the length of fermentation. Some industrially produced soy sauce starts with hydrolyzed vegetable protein (not necessarily soy) and may be sweetened with corn syrup and colored with caramel to mimic the flavor and color of fermented soy sauce.
Soy sauce is not all the same and, since we prefer simplicity in the test kitchen, we were hoping one clear winner would emerge from our tasting. No such luck. Our tasters liked one type of soy sauce for plain, uncooked applications and an entirely different one for cooked dishes. How about being able to say the best soy sauce is made in one particular country? Sorry: The tasters chose two different nations' products, depending on how it was used. Method of brewing? Again, they split between an artisanal soy and a mass-produced one (albeit one aged for months, not days). Would saltiness be the favored attribute? No, one had the least amount of salt of the 12 in our lineup, the other had the most. Clearly, these results underscored the fact that there's no "one-size-fits-all" soy sauce.
An important clue came when we tested lower-sodium (also called "light") soy sauces. (Lower-sodium soy sauces start as regular soy sauce, then some sodium is removed by filtering or ion exchange.) The lower-sodium soy sauces actually beat the regular soy sauces in a plain taste test but lost out in cooked applications. Why? Cutting down on the salt let some of the other flavors take the stage, leaving a delicate, complex soy taste in the foreground. But once cooked, the delicate flavors dissipated.
These delicate, nuanced flavors develop during the fermentation process. Generally, the longer the soy sauce ages, the more flavor it will develop—like wine. These flavorful esters are volatile, however and cook off when heated. In fact, if you cook soy sauce for any length of time you'll drive off the aroma-making it advisable to add more back at the end of cooking.
Our winning cooking soy sauce, with a more robust flavor that held up during the boiling and reduction of the teriyaki sauce, is higher in the nonvolatile flavor “Maillard” components. In the Maillard reaction, sugars and amino acids react to heat, causing browning and bringing about a richer, more savory flavor -- like searing meat before making pot roast. In fact, this sauce was the only soy sauce we tasted that had significant sugar content: two grams per tablespoon. Combine that sugar with a high salt content and the overall flavor profile of the dish is improved.
Our two winners also represent two very different manufacturing styles. Our cooking favorite is fermented for three to six months in 20-foot-tall fiberglass holding tanks. In contrast, our dipping favorite is unpasteurized, and is hand-stirred and fermented in sixty 150-year-old cedar kegs. The sauce is then double-fermented over an unusually long period, which produces a complex bouquet of aroma and flavor and mellows salt impact, making it preferable for dipping and non-cooking applications.