Soy sauce (醤油, shōyu) is Japan's foundational fermented seasoning: a clear, savoury liquid brewed from soybean and wheat cultured with kōji mould, brined into a mash and matured. Japan's Agricultural Standard defines five types and three methods, and true-brewed soy sauce makes up about 90% of the 681,000 kL the country shipped in 2024.
This is our main guide to soy sauce, written for chefs and curious cooks alike: what it is, the five JAS types and how they differ, how it is brewed, how it is graded, and how a kitchen uses each style. It sits inside our Fermented Masterclass.
What Is Soy Sauce?
Soy sauce (醤油, shōyu) is a clear, fermented liquid seasoning. Under Japan's Agricultural Standard (JAS) it is made from soybean, usually with wheat, steamed and cultured with kōji mould to make shōyu-kōji; this is mixed with brine into a moromi (もろみ) mash, fermented and matured, then pressed to a clear liquid. Kōji enzymes do the work, turning protein into amino acids and starch into sugars.
It is the keystone condiment of Japanese cooking and, with miso, one of the two great soybean ferments, both built on the same kōji enzymes. Production is overwhelmingly domestic and concentrated: in 2024 Japan had 1,013 soy-sauce producers shipping 681,019 kL, a long, slow decline from around 6,000 producers in 1955.
For a chef, the useful framing is that soy sauce is brewed, not blended: a real shōyu is a fermented product with months or years of maturation behind it, which is why a craft soy tastes of far more than salt and colour.
Source: MAFF JAS standard for soy sauce (definition and method) and Japan Soy Sauce Association 2024 national statistics (producer and volume figures). The kōji enzyme mechanism is established food science.
The Five Types of Soy Sauce
JAS recognises five types of soy sauce, separated mainly by the soybean-to-wheat ratio and the colour that follows from it. The market is dominated by koikuchi, the all-purpose dark soy, at about 85% of output; the other four are regional specialities a chef reaches for by job.
| Type | Japanese | Character and origin | Share (2024) |
|---|---|---|---|
| Koikuchi (dark) | こいくち | Equal soybean and wheat; the balanced all-purpose standard | 84.9% |
| Usukuchi (light colour) | うすくち | Kansai origin; paler and a little saltier, to protect delicate dishes | 11.5% |
| Tamari | たまり | Chubu; little or no wheat, thick and dense, reddens when heated; the sashimi soy | 2.1% |
| Saishikomi (twice-brewed) | さいしこみ | San-in and Kyushu; brewed with soy sauce in place of brine, dark and sweet | 1.0% |
| Shiro (white) | しろ | Hekinan, Aichi; wheat-dominant, pale amber, mild but sweet; for soups and chawanmushi | 0.6% |
The practical lesson is to match the type to the task. Koikuchi does most of the daily work, from dipping to simmering. Usukuchi keeps a dish pale where colour matters. Tamari is the thick, wheat-free soy for sashimi and glazes. Saishikomi is a rich finishing soy. Shiro keeps clear soups and custards almost colourless. Note that soy-based condiments such as ponzu, tsuyu, tare and dashi-soy are made from soy sauce but are not themselves JAS soy sauce.
Source: type definitions and soybean-wheat ratios from the MAFF JAS standard; regional origins and character from the Japan Soy Sauce Association; volume shares from JSA 2024 statistics.
How Is Soy Sauce Made?
True-brewed (honjōzō) soy sauce is made by culturing steamed soybean and roasted, cracked wheat with kōji mould to make shōyu-kōji, mixing that with brine into a moromi mash, then fermenting and maturing it for months to a couple of years before pressing to a clear liquid. Honjōzō accounts for about 90% of Japanese soy sauce; the rest is made by two mixed methods that add seasoning liquids.
| Method | Japanese | What it is | Share (2024) |
|---|---|---|---|
| True-brewed | 本醸造 (honjōzō) | Moromi fermented and matured naturally; enzymes only as an auxiliary | 89.8% |
| Mixed-brewing | 混合醸造 | Brewed moromi with seasoning liquid added, then fermented further | 0.5% |
| Mixed | 混合 | Seasoning liquids blended into finished brewed soy sauce | 9.7% |
During the moromi ferment, kōji enzymes break protein into amino acids and starch into sugars while yeast and lactic-acid bacteria build aroma and acidity. The matured mash is pressed to raw soy sauce (kiage), then refined and usually pasteurised. The traditional craft ferments in large wooden barrels (木桶, kioke; locally koga on Shodoshima), whose wood and brewery harbour the resident microbes that give each house its character. That craft has thinned: of roughly 3,000 wooden barrels still in use across Japan, over 1,000 are on Shodoshima in Kagawa, which has brewed soy sauce for 400 years, some barrels up to 150 years old.
For a chef, the takeaway is that the method is the quality signal. A barrel-aged honjōzō from a craft house is a different ingredient from a fast mixed soy, in the same way a barrel miso differs from a quick one.
Source: brewing sequence and the three methods from the MAFF JAS standard; method shares from JSA 2024 statistics; the kioke craft and barrel figures from the Shodoshima Soy Sauce Cooperative and the Japan National Tourism Organization.
How Is Soy Sauce Graded?
JAS grades soy sauce chiefly by total nitrogen, a proxy for amino-acid richness: the more nitrogen, the deeper and more savoury the soy, and the higher the grade. For koikuchi honjōzō the tiers run from Standard up to Extra-select, and final grading combines instrumental analysis with sensory inspection by certified tasters.
| Grade | Japanese | Total nitrogen (koikuchi honjōzō) |
|---|---|---|
| Standard | 標準 (Hyōjun) | 1.20% or more |
| Upper | 上級 (Jōkyū) | 1.35% or more |
| Special | 特級 (Tokkyū) | 1.50% or more |
| Extra-select | 特選 (Tokusen) | 1.65% or more |
The standard also sets colour (against an official soy-sauce colour scale), salt-free soluble solids and alcohol per type. In 2024 about 53% of national output was JAS-inspected. The chef's reading: total nitrogen on a label is a genuine richness guide, and a higher tier is worth it where the soy is tasted directly, as a dip or a finish, more than where it disappears into a braise.
Source: grade tiers and test criteria from the JSA information centre and the MAFF JAS standard; inspection share from JSA 2024 statistics. Exact per-type numeric thresholds sit in the full JAS document.
Popular Products
Four soy sauces that show the range, from our craft house everyday soy to a twice-brewed speciality:
Shibanuma Barrel-Aged Unpasteurised Soy Sauce, 300g
Shiho no Shizuku, the nama (unpasteurised) soy from our house brewer Shibanuma, an eighteen-generation cedar-barrel house in Ibaraki. Living, barrel-aged koikuchi with depth a pasteurised soy cannot match. The one to taste neat.
Shibanuma Japanese Dark Soy Sauce, 18L
Everyday koikuchi, the all-purpose dark soy that does most of the work in a Japanese kitchen, from a craft house and in the catering cube. The workhorse for dipping, simmering and seasoning at volume.
How Chefs Use Soy Sauce
Soy sauce is the all-purpose Japanese seasoning, and the type does the choosing. Koikuchi covers general cooking, dipping and simmering; usukuchi goes where the colour must stay pale, as in clear simmered dishes; tamari suits sashimi and glazes that should redden with heat; saishikomi works as a rich finishing or sashimi soy; shiro keeps soups and chawanmushi almost colourless. One soy does not fit every job.
It is also the base for a whole family of derived condiments, dashi-shōyu, tsuyu, tare, ponzu and dressings, which extend it across the table without being soy sauce in the JAS sense. The everyday rule that matters is heat and timing: a finishing soy added late keeps its aroma, while soy cooked long loses the top notes and leaves mostly salt and colour, which is fine in a braise but a waste of a craft bottle.
Our steer for a working kitchen: keep an everyday koikuchi for cooking and a better barrel-aged or twice-brewed soy for finishing and dipping, and treat them as two jobs, not one bottle. (Pairing and technique detail beyond the type-led uses above is our own kitchen practice; the record flags chef-level specifics as a gap.)
Source: type-led uses and the derived-condiment family from the Japan Soy Sauce Association information centre; broader kitchen guidance is SushiSushi practice.
Frequently Asked Questions
What is soy sauce made from?
Japanese soy sauce is made from soybean, usually with roughly equal wheat, plus salt, kōji mould and water. The soybean and wheat are cultured with kōji to make shōyu-kōji, mixed with brine into a moromi mash, then fermented and matured for months to a couple of years and pressed to a clear liquid. Tamari uses little or no wheat; white soy is wheat-dominant.
What are the five types of soy sauce?
Japan's JAS standard defines five: koikuchi (the all-purpose dark soy, about 85% of output), usukuchi (paler and a little saltier, from Kansai), tamari (thick, wheat-free, for sashimi), saishikomi (twice-brewed, dark and sweet) and shiro (wheat-dominant white soy, pale and mild). They differ mainly in the soybean-to-wheat ratio and the resulting colour and use.
What is the difference between tamari and soy sauce?
Tamari is a type of Japanese soy sauce, not a separate thing. It is brewed with little or no wheat, so it is thicker, darker and denser in umami than standard koikuchi soy, and it reddens when heated. Because it usually contains little or no wheat, many tamari products are suitable for gluten-free diets, though you should always check the individual label.
What does honjōzō mean on a soy sauce label?
Honjōzō means true-brewed: the soy sauce was made by naturally fermenting and maturing a moromi mash, with enzymes used only as an auxiliary, rather than by adding seasoning liquids. It is the traditional method and accounts for about 90% of Japanese soy sauce. On a label it signals a genuinely brewed product rather than a blended one.
How should soy sauce be stored?
Keep soy sauce cool and out of direct light, and once opened use it within a few weeks to a couple of months for best flavour, refrigerating after opening to slow oxidation. Unpasteurised (nama) soy sauces are more delicate and benefit most from cold storage. Soy keeps for a long time on salt alone, but its aroma fades with air and warmth.
Where to Buy Soy Sauce in the UK
If you are looking to buy soy sauce in the UK, we keep a range with fast delivery across the UK, from everyday koikuchi to barrel-aged, twice-brewed and kōji-finished craft soys, including our house brewer Shibanuma. Start with a good koikuchi for cooking and a finishing soy for the table.
For more, browse the Fermented Masterclass, or read about kōji, the mould that makes soy sauce possible, and miso, its sister soybean ferment.
Technical data sourced from Japan's MAFF Agricultural Standard (JAS) for soy sauce and the Japan Soy Sauce Association's 2024 national statistics and information centre, with craft and heritage detail from the Shodoshima Soy Sauce Cooperative and the Japan National Tourism Organization, and house-producer detail from Shibanuma Soy Sauce Co. Ltd (Tsuchiura, Ibaraki, founded 1688). Type, method and grade definitions follow the JAS standard; market figures are JSA 2024; enzyme and fermentation mechanisms are established food science.
