The flavouring agent in Japanese cooking, shoyu (soy sauce) is made from soybeans (…duh), wheat, salt and water. Japanese recipes use soy sauce for its rich flavour in addition to its kick of salt.
Because it is the main flavouring agent in Japanese cuisine, it’s important to use a Japanese soy sauce when cooking Japanese food. Japanese soy sauces are less viscous and more delicately flavoured than other Asian soy sauces, so please, please, puh-lease don’t use Chinese soy sauces in Japanese recipes. Don’t get me wrong, it’s not a snob thing – it’s a flavour thing.
What to buy
A staple in the stock and sauce trifecta of dashi, shoyu, mirin, it’s worth buying a large bottle if you’re going to be doing any substantial amount of Japanese cooking. Check the label, though, because many brands skip the time-consuming natural fermentation process use chemicals instead, leading to a harsher, more acidic flavour profile. Welcome additives, however, are things like kombu or katsuo stock, which add umami.
Koikuchi (Regular) shoyu: If you’re only going to buy one shoyu, then this is it. It’s most versatile, and if you use it where a recipe calls for light shoyu, you won’t have strayed too far. A regular bottle of Kikkoman soy sauce at your local grocery store fits this category, but I prefer to buy an imported brand.
Usukuchi (Light) shoyu: Light means light in colour, not in salt. In fact, usukuchi shoyu is higher in salt content than regular shoyu. It’s popularly used in western Japan (the Kansai region) because of its more delicate colour.
Low sodium soy sauce: This is the one to buy if you’re looking for a lower-sodium substitute.
Tamari: A historical precursor to shoyu, tamari is used in Japan for dipping sushi and sashimi because it’s more viscous and will stick to the fish. (Usually) made without wheat, gluten-intolerant food lovers can use tamari as a shoyu substitute. Its salt content is roughly the same, so use in equal parts, but its darker colour and thicker consistency will mean that your results will be somewhat different than if using regular shoyu.
Store your shoyu capped tightly in a cool, dark place for up to a year.