Ingredient

Soy sauce

Soy sauce is a seasoning, a colouring and a source of savoury depth, and most kitchens use one bottle for all three jobs when the tradition it comes from uses two or three different ones. Getting that right is the single biggest improvement available to home stir-frying.

Why it is not simply salty water

Soy sauce is fermented — soya beans and usually wheat, broken down over months by moulds, yeasts and bacteria. Fermentation cuts the proteins into free amino acids, and one of those, glutamate, is what the tongue reads as savoury depth. That is why a spoonful of soy sauce in a beef stew or a tomato sauce makes it taste meatier without tasting Chinese.

It also means soy sauce carries aroma as well as taste, and aroma is fragile. Soy sauce added at the beginning of a long simmer contributes salt and colour; added at the end it contributes its own smell as well.

The main kinds

Light soy sauce

The everyday seasoning soy, despite the name — saltier and thinner than dark, not lower in sodium. This is what a Chinese recipe means by "soy sauce" unqualified.

Dark soy sauce

Aged longer, often with added molasses or caramel. Thicker, much darker, less salty, slightly sweet. Used for colour and body, usually a teaspoon or two rather than a tablespoon.

Japanese shoyu (koikuchi)

The standard Japanese soy. Rounder and more aromatic than Chinese light soy, with more wheat.

Usukuchi

Lighter in colour and saltier than koikuchi, used where the dish should not go brown.

Tamari

Japanese, made with little or no wheat, so it is often — but not always — gluten free. Darker and richer, and it is the one to check labels on.

Kecap manis

Indonesian, thick and heavily sweetened with palm sugar. A different ingredient, not a substitute.

Using it well

• Treat it as salt. Soy sauce is salty enough that adding it and salting separately is how a dish ends up inedible. Season with one, then check.
• Add it to the hot pan, not to the food. Splashed around the edge of a hot wok it sizzles and caramelises for a second before it hits the food, which is where a good deal of stir-fry aroma comes from.
• Use dark soy for colour and light soy for taste. A braise that looks pale and tastes right needs a teaspoon of dark; one that looks right and tastes flat needs light.
• Do not boil it hard for a long time. It goes harsh and bitter. Long braises take it early and in moderation.
• Off the heat it is a condiment. A few drops on a fried egg, on avocado, on roasted mushrooms.

Outside East Asian cooking

Soy sauce is one of the most useful bottles in a Western kitchen too, used in quantities small enough that nobody identifies it.

• A teaspoon in a beef stew, a shepherd's pie or a gravy, for depth.
• A splash into a tomato sauce, which does the same job as anchovy without the fish.
• In a marinade for anything grilled, where the sugars help browning and the salt helps the meat hold moisture.
• In a mushroom pan, where it doubles the savoury note mushrooms already have.
• Half a teaspoon in a French onion soup, which is close to cheating.

Common questions