Overview
Fish sauce is liquid umami — salty, funky, and deeply savory, used by the tablespoon to anchor Thai curries, Vietnamese dressings, and pad thai. Its flavor is more complex than plain salt, which is why plain soy sauce alone falls a little short.
A splash of rice vinegar closes most of the gap; seaweed closes the rest.
Why it works
Fish sauce's savoriness comes from fermented fish proteins breaking down into glutamates. Fermented soy — soy sauce, tamari, miso — produces the same compounds through the same process, just from beans instead of fish.
What soy sauce lacks is fish sauce's briny, oceanic edge, which a strip of kombu or a splash of rice vinegar approximates.
How to make it
For each tablespoon of fish sauce, combine 1 tablespoon of soy sauce with 1/2 teaspoon of rice vinegar. For a closer match, simmer the soy sauce for 5 minutes with a 2-inch strip of dried kombu, then strain and cool.
Add it at the same step the recipe adds fish sauce — usually early in a curry, at the end in a dressing.
What you lose
The particular fermented funk that makes fish sauce unmistakable. The soy-vinegar blend is savory and bright but cleaner-tasting — in a boldly spiced curry no one will notice; in a nuoc cham dipping sauce, a purist might.
Store-bought vegan fish sauce is the answer when the sauce is the star.
Adjustments that matter
In dressings and dipping sauces, where fish sauce is front and center, use a vegan fish sauce or add a pinch of crumbled nori to the soy blend. In cooked dishes — curries, stir-fries, fried rice — the plain soy-vinegar blend is indistinguishable.
Remember fish sauce is saltier than it tastes; season the finished dish before adding extra salt.
Common mistakes
Swapping soy sauce 1:1 without the vinegar and ending up flat. Using Worcestershire sauce as the swap — traditional Worcestershire contains anchovies, so it is not plant-based. And adding the seaweed broth too early in a delicate dressing, where its iodine edge can dominate.