Soy sauce is delicious, but choosing the best often comes down to "my brand versus your brand." Ditch brand loyalty and look at the label instead: If yours has been brewed or fermented, and proudly states it, it will be better than sauce made using methods like hydrolysis, often used to keep costs low.
Photo by Ben Chun.
Cook's Illustrated tested a variety of soy sauces, and while their favourite pick isn't freely available, they do explain in the article below what it is that makes a good soy sauce, how the best soy sauces are made, and how you can tell a good one from a bad one if you're trying to choose in the store:
The six top-ranking sauces we tasted are made the old-fashioned way: fermented, or "brewed." The process starts by culturing boiled soybeans and roasted wheat with a mould that creates a mixture called koji, which functions like a sourdough starter: It begins to break down the carbohydrates and proteins and provides a sauce's unique flavour profile. (Some manufacturers have used the same koji for decades or even centuries; Kikkoman, for example, claims that its koji dates back 300 years.) From there, salt and water are added, and the mash, now called moromi, is left to ferment for anywhere from a few months to years. During that time, lactic acid bacteria work with yeasts to further break down proteins and carbohydrates into a mix of flavorful compounds (alcohols, esters, peptides, and acids), including glutamic acid (a major source of umami), and the clear-coloured mash darkens to a deep reddish brown. Finally, when the manufacturer decides it's ready -- in our lineup, this period ranged from four months to two years -- the mash is pressed to extract soy sauce, which is then pasteurised. The heat kills bacteria, stops fermentation, and launches the Maillard reaction, breaking down the proteins into hundreds of new compounds that give soy sauce rich caramelised flavour and aroma.
The two lower-ranking soy sauces are made by hydrolysis, a process that takes just two to three days and involves no wheat or even soybeans, per se. Instead, defatted soy flour (or other flours, such as corn) is boiled with hydrochloric acid to separate the amino acids, which are then neutralized with sodium carbonate. The resulting hydrolyzed vegetable protein is doctored with caramel colour, corn syrup, and salt to make it look and taste more like fermented soy sauce.
There's a great graphic that outlines how the process described above actually works, along with some visuals, but the bottom line is clear: If you're looking for a great soy sauce that will be a delicious all-around condiment for dipping, marinating, and seasoning, make sure the brand you're buying has been fermented or brewed. In the case of soy sauce, shortcuts sacrifice a lot of flavour.
Brewing a Better Soy Sauce [Cook's Illustrated]