Fish sauce is made from anchovies layered with salt and left to ferment for months, sometimes more than a year. What runs off is a clear, amber liquid that smells strong straight from the bottle, but does something magical in the pan: it seasons with salt and deep, savoury umami at the same time.
In the Thai kitchen it plays the role that salt plays in ours. Thai food is about balance between salty, sour, sweet and hot, and fish sauce is the salty corner of that square. It goes into almost everything: curries, soups, stir-fries, dipping sauces and dressings for som tam and larb. On the table it is served as nam pla prik, with sliced chili and a squeeze of lime, so everyone can season their own plate.
Buying a bottleWithout fish sauce, Thai food tastes flat. With it, everything wakes up.
How to choose a good one
Read the label
The best bottles list only anchovy and salt, perhaps a little sugar. Skip those with flavour enhancers and colouring.
Look at the colour
Clear, reddish amber is a good sign. Very dark or cloudy sauce is often old or of lower quality.
Add it at the end
Season a little at a time and taste. A few drops change the whole dish, and it is easy to go too far.
Not optional, and not replaceable with salt or soy sauce. Buy a good bottle: it lasts a long time in the cupboard and you will reach for it every time you cook Thai.