In Japan, you'll find several distinct types, each with specific uses:
Koikuchi (Dark Soy Sauce) - This is your everyday soy sauce, accounting for roughly 80% of production in Japan. It has a rich, salty flavour with a hint of sweetness from the wheat used in fermentation. Kikkoman is the most recognisable brand globally, and whilst purists might seek out artisanal brands, it's perfectly acceptable for home cooking. Once opened, store it in a cool, dark cupboard where it'll keep for at least six months, though the flavour is best within three months.
Usukuchi (Light Soy Sauce) - Despite its name, this isn't lower in sodium—it's actually slightly saltier. The "light" refers to its paler colour, achieved through shorter fermentation. Japanese cooks use it when they want seasoning without darkening dishes, particularly in delicate soups or with pale vegetables. It's less common outside Japan but worth seeking out if you're serious about authentic cooking.
Tamari - Originally a by-product of miso production, tamari contains little to no wheat, making it the choice for those avoiding gluten. It has a deeper, more complex flavour than koikuchi and is excellent for dipping sashimi or as a finishing sauce.
Saishikomi (Twice-Brewed Soy Sauce) - For the truly dedicated, this premium variety is fermented twice, creating an intensely rich, almost syrupy sauce. It's expensive and used sparingly as a finishing drizzle rather than for cooking. You'll mainly find it in specialist Japanese shops.
