Chinese Soy Sauce: How Real Jiangyou Is Actually Brewed

Walk into an old-style soy sauce yard in Guangdong on a hot afternoon and the first thing that hits you is not the smell but the geometry. Hundreds of waist-high clay jars stand in rows across an open courtyard, each capped with a conical bamboo hat, each holding a dark, viscous mash slowly cooking in direct sunlight. Someone walks the rows with a wooden paddle, stirring. That is the entire technology. It has not changed meaningfully in centuries.

This is how jiangyou (酱油) — Chinese soy sauce — is supposed to be made, and it is worth understanding because most of what is sold under that name today is made another way entirely.

From Meat Paste to Bean Paste

Soy sauce did not begin with soy. Its ancestor is jiang (酱), a category of salted fermented pastes documented in Chinese texts from the Zhou period onward. The earliest versions were made from meat and fish — salted, packed into jars with grain ferment and wine, and left to break down into a savoury paste. Related products appear in the ritual and dietary records of the Zhou court, where specific jiang were prescribed alongside specific dishes.

Soybeans replaced meat over time for the obvious reason: they were vastly cheaper and available everywhere. By the Han dynasty, bean-based jiang was a household staple. The liquid that separated and pooled on top of a maturing jar — initially a by-product — turned out to be the most flavourful part, and eventually production was reorganised to maximise it. That liquid is soy sauce.

From China the technique travelled with Buddhist monks and traders to Japan, Korea and Southeast Asia, where it diverged into distinct traditions. Japanese shoyu, for instance, typically uses roughly equal parts soybean and wheat; most Chinese soy sauce uses far more soybean than wheat, which is a large part of why the two taste different.

The Traditional Process

Step One: Making Qu

Everything begins with qu (曲), the mould starter. Soybeans are soaked and steamed until soft; wheat flour or roasted crushed wheat is mixed in. The mixture is spread in shallow trays or on bamboo mats in a warm, humid room and inoculated with Aspergillus oryzae or Aspergillus sojae.

Over two to three days the mass turns yellow-green with mould growth and warms noticeably from microbial activity. Traditional makers judge readiness by colour, smell and the temperature felt through the back of a hand. The mould's job is enzymatic: it produces proteases that will later break soy protein into amino acids, and amylases that convert starch into sugars.

Step Two: The Brine Mash

The mouldy koji is transferred to jars or vats and mixed with salt water. The salt concentration is high enough to exclude spoilage organisms while permitting salt-tolerant yeasts and lactic acid bacteria to work. The resulting mash is called jiang lao or, borrowing the Japanese term used widely in food science, moromi.

Step Three: Sun Exposure and Time

This is the stage that distinguishes traditional Chinese soy sauce. The jars sit outdoors, uncovered to the sun by day and to dew by night — a practice called ri shai ye lu, sun-dried by day, dew-soaked by night. The bamboo hats go on when it rains and come off when it is clear.

Daily temperature swings drive the fermentation in a way that constant-temperature tanks do not. Sunlight and evaporation concentrate the mash and deepen its colour through Maillard reactions. Workers stir the jars on a schedule to aerate and equalise.

Duration: six months minimum, commonly a full year, sometimes three years for premium grades. There is no way to compress this. Amino acid content, aromatic esters and colour all develop on their own timetable.

Step Four: Drawing Off

The finished sauce is extracted — traditionally by lowering a perforated bamboo basket into the jar and ladling the clear liquid that seeps in, or by pressing the mash through cloth. The first draw is the finest and is sold as premium tou chou, "first extract." Later draws from re-brined mash yield progressively lighter grades. The sauce is then pasteurised, settled and bottled.

The single most useful number on a Chinese soy sauce label is amino acid nitrogen content, given in grams per 100 millilitres. Higher means more protein has been broken down into savoury amino acids. Premium grades sit around 0.8 g/100ml and above.

Light, Dark, and the Difference That Matters

Chinese cooking uses two soy sauces that are not interchangeable, and confusing them is the most common mistake in Western kitchens attempting Chinese food.

• Light soy sauce (生抽, shengchou). Thin, reddish-brown, distinctly salty, drawn earlier in the process. This is the default seasoning sauce — for stir-fries, marinades, dipping, soups, and anywhere you want salt plus savour without changing the colour of the dish. When a Chinese recipe says "soy sauce" without qualification, it usually means this.
• Dark soy sauce (老抽, laochou). Aged longer, often with caramel or molasses added, noticeably thicker, much darker, and less salty than light soy. Its purpose is colour and a faint sweetness. It is what makes red-braised pork mahogany. Used in small quantities — a teaspoon, not a tablespoon.

Beyond the two main types:

• Mushroom dark soy — dark soy infused with straw mushroom, adding depth for braises
• Seasoned soy for steamed fish — lighter, sweetened, aromatic, poured over at the table
• Sweet soy (酱油膏) — thick and syrupy, used in Chaozhou and Southeast Asian Chinese cooking
• Tamari-style bean-only sauces — wheat-free, made in some inland regions

Regional Reputations

Soy sauce quality follows climate, because sun exposure is a production input.

• Guangdong — the acknowledged centre. Long hot summers and strong sun suit outdoor jar fermentation. Zhongshan, Foshan, Yangjiang and Kaiping all have historic yards; Guangdong-style light soy is the national reference point.
• Fujian — similar climate, distinctive sweeter profile in some houses.
• Jiangsu and Zhejiang — associated with darker, rounder sauces suited to the region's red-braising and sweet-savoury cooking.
• Northern China — shorter warm season means a heavier reliance on indoor fermentation and on bean paste rather than clear sauce.

Brewed Versus Blended: Reading the Label

Industrial production created a shortcut called acid-hydrolysed vegetable protein — defatted soy meal boiled in hydrochloric acid, neutralised, coloured and flavoured. It takes days rather than months and produces a liquid that is salty and brown but flat, lacking the aromatic complexity fermentation generates.

Chinese national standards distinguish brewed soy sauce (酿造酱油) from blended or prepared soy sauce (配制酱油). What to look for:

• The words 酿造酱油 on the label, or "naturally brewed" in English
• A short ingredient list — water, soybeans, wheat, salt, and little else
• Amino acid nitrogen figure — the higher the better; premium grade is the top tier
• Absence of hydrolysed vegetable protein in the ingredients
• Foam behaviour — shake the bottle. Well-brewed sauce forms fine, dense foam that lingers; thin sauces foam coarsely and collapse fast.

Cooking With It Properly

A few things worth knowing, learned mostly by getting them wrong:

• Add light soy along the hot edge of the wok, not into the middle of the food. It sizzles and the aroma blooms — a technique Cantonese cooks call "pouring along the rim."
• Do not boil dark soy for long. Extended high heat turns its sweetness bitter. Add it early enough to colour, not so early it scorches.
• Salt separately, if at all. Light soy is roughly 15–18 percent salt. Season the dish after it is in.
• Store it cool and closed. Oxidation dulls aroma within a few months of opening. Refrigeration after opening extends the useful life considerably.
• Do not substitute Japanese soy blindly. Higher wheat content makes shoyu sweeter and more alcohol-aromatic; in a Cantonese steamed fish it reads as slightly off.

Quick Reference

• Chinese name: 酱油 jiangyou
• Ancestor: 酱 jiang, fermented salted pastes from the Zhou period
• Key organism: Aspergillus oryzae / sojae
• Traditional maturation: 6 months to 3 years in open clay jars
• Two essential types: Light (生抽) for seasoning, dark (老抽) for colour
• Quality marker: Amino acid nitrogen g/100ml, plus "酿造" brewed designation

Note on sources: this article draws on the standard published account of Chinese fermentation history and on Chinese national labelling standards distinguishing brewed from blended soy sauce. Historical details on jiang follow classical dietary records of the Zhou period; production description reflects documented practice at traditional open-yard soy sauce works in Guangdong.