Soy sauce is so ubiquitous that most people never think about it. It sits on the table at every Japanese restaurant, gets poured without ceremony, and is treated as a single, uniform product. But soy sauce is a category, not an ingredient, and the differences between types are significant enough to change how your food tastes.

I became interested in soy sauce varieties after a meal at a small sushi restaurant where the chef offered three different soy sauces for different courses. The contrast was striking — what I had always thought of as one flavour turned out to be many.

How Soy Sauce Is Made

Traditional soy sauce (shoyu) is made from soybeans, wheat, salt, and water, fermented with a mould called koji (Aspergillus oryzae) for anywhere from six months to several years. The fermentation process produces the complex flavour — hundreds of aromatic compounds develop during this time, giving naturally brewed soy sauce a depth and nuance that chemically produced alternatives cannot replicate.

Industrial soy sauce, which accounts for the majority of what is sold in supermarkets, shortcuts this process through hydrolysis — breaking down soy protein with hydrochloric acid rather than fermentation. The result is faster and cheaper but produces a one-dimensional, harsh-tasting product. For any serious cooking or table use, naturally brewed soy sauce is worth the modest price premium.

The Main Japanese Types

Koikuchi (dark soy sauce). This is the standard, accounting for about 80% of Japanese soy sauce production. It uses roughly equal parts soybean and wheat, producing a balanced flavour with a deep reddish-brown colour. When a Japanese recipe calls for soy sauce without specifying a type, koikuchi is assumed. It is versatile, with a good balance of saltiness, sweetness, and umami. This is the soy sauce that sits on sushi bar tables.

Usukuchi (light soy sauce). Do not let the name fool you — light refers to colour, not sodium. Usukuchi is actually saltier than koikuchi, with a paler colour and a thinner, more delicate flavour. It is used in cooking where you want soy sauce flavour without darkening the dish — light-coloured soups, simmered vegetables, and delicate preparations where appearance matters.

Tamari. Made primarily or entirely from soybeans with little or no wheat. Tamari is thicker, darker, and richer than koikuchi, with a more intense umami flavour and a slight viscosity. It is the best soy sauce for dipping sashimi, in my opinion — the concentrated soybean flavour complements raw fish beautifully. For those avoiding gluten, wheat-free tamari is available.

Saishikomi (twice-brewed). Instead of using salt water in the second stage of brewing, saishikomi uses previously brewed soy sauce. This double fermentation produces an intensely flavoured, darker sauce that is almost syrupy. It is a premium product, best used sparingly for dipping rather than cooking.

Shiro (white soy sauce). The opposite of tamari — made mostly from wheat with minimal soybean. It is very pale, almost golden, with a sweet, delicate flavour. Shiro is used in dishes where you want umami without colour, such as clear soups and some types of sashimi dressing.

Using Soy Sauce With Sushi

At the sushi bar, a few principles apply. Pour a small amount of soy sauce into the dish — just enough to wet the bottom. You can always add more, but a dish brimming with soy sauce suggests you plan to drown your food.

For nigiri, turn the piece fish-side down and dip lightly. The rice should never touch the soy sauce — it absorbs too much, falls apart, and overwhelms the flavour of the fish. If the chef has already applied nikiri (a blended soy sauce brushed onto the fish), skip the dipping entirely.

For sashimi, dip the corner of each slice. The fish should be lightly touched by the sauce, not saturated. Strong-flavoured fish like tuna can handle more soy sauce than delicate white fish, which needs barely a whisper.

Nikiri: The Sushi Chef’s Soy Sauce

At quality sushi restaurants, the chef often uses nikiri rather than standard soy sauce. Nikiri is a blend of soy sauce, mirin, and dashi, simmered together and cooled. The result is less salty, more complex, and specifically calibrated to complement raw fish.

Some chefs personalise their nikiri further, adjusting the ratios for different fish or even different pieces within a course. This level of attention is part of what separates a good sushi bar from a great one. The nikiri is applied with a brush (hake) in a single, precise stroke across the top of each piece of nigiri.

Buying and Storing Soy Sauce

For everyday cooking and table use, buy a naturally brewed koikuchi from a reputable Japanese brand. Kikkoman Marudaizu (the premium line, not the standard) is widely available and excellent. For sashimi dipping, invest in a good tamari.

Store soy sauce in the fridge after opening. Exposure to air and light degrades the flavour over time, and refrigeration slows this process. If your soy sauce has been sitting at room temperature for months, replace it — the flavour will have flattened and the colour darkened.

Buy sizes appropriate to your usage. A massive bottle is economical but will deteriorate before you finish it if you cook Japanese food only occasionally. A smaller bottle used within a month or two will taste better throughout its life.

The difference between good soy sauce used properly and ordinary soy sauce used carelessly is profound. It costs almost nothing more but improves every dish it touches.