Tom Chua — Hue's Raw Prawns Fermented With Galangal, Garlic and Chilli

Tôm chua is Hue’s best-known fermented preserve, and the most approachable of the central Vietnamese fermented foods — gently sour, sweet, fragrant with galangal, and not strong on the nose.

The prawns are cooked by fermentation, not heat

Looking at a jar of bright red tôm chua, most people assume the prawns were boiled. In fact they go in raw.

Fresh small prawns are washed, their whiskers trimmed, and mixed with shredded galangal, garlic, chilli, salt and cooked glutinous rice, then packed down tightly in a jar. Left somewhere warm for a few days, the glutinous rice ferments and produces lactic acid — and that acid is what sets the proteins in the prawns, turning the shells red and firming the flesh.

The principle is the same as fermented pork roll: the food is cooked and preserved by fermentation rather than by heat.

Galangal is not there only for aroma. Galangal and garlic suppress spoilage bacteria and keep the batch fermenting in the right direction.

How long until it is ready

Depending on the weather, usually five to seven days in hot weather, longer when it is cool.

Not yet — the prawns are still translucent, the salt dominates, no sourness has developed.
Right — evenly red prawns, firm flesh, gentle sourness and a sweet finish.
Too long — sharply sour, the prawns gone soft.

A bought jar is normally already at the right stage. Refrigeration slows the process and keeps it there.

What to eat it with

The classic Hue way is boiled pork rolled in rice paper:

Boiled pork belly, thinly sliced, still warm.
Rice paper, noodles and herbs: lettuce, mint, perilla, green banana, sour starfruit.
Tôm chua spooned alongside, with a little sugar added if you want it softer.

It also goes with hot rice, plain rice porridge, or as a dip for boiled vegetables.

Choosing a jar

Whole prawns, evenly red, not broken up.
Thick liquid, not cloudy or gritty. Cloudy liquid or white foam on top means the jar has spoiled.
Visible shredded galangal, garlic and chilli — a jar light on galangal will be light on aroma.
It should smell fragrant and sour, not sharply pungent.

A jar left in the heat keeps fermenting and turns more sour, so refrigerate it once you have bought it.

Keeping it and carrying it

Refrigerated it lasts several weeks; close it tightly after each use.
Use a clean, dry spoon — water or oil getting in will spoil the jar.
On a plane it has to go in checked baggage, up to three litres or three kilos per person.