Nước màu — Vietnamese caramel sauce — is a deeply reduced, slightly bitter caramel made by cooking sugar until it darkens to a deep amber-brown, then carefully adding fish sauce or water. It is used as a colouring and flavouring agent in Vietnamese braises (particularly thịt kho — caramelised pork belly), providing the deep reddish-brown colour and a bitter-sweet depth that soy sauce does not provide.
**The caramelisation:** 1. Place white sugar (100g) in a dry, heavy pan. 2. Heat on medium until the sugar begins to melt at the edges. 3. Do not stir once the sugar begins to melt — stirring can cause re-crystallisation. 4. The sugar melts, then bubbles, then darkens through pale amber to deep amber-brown. 5. At the deep amber stage (approximately 185–190°C): carefully add fish sauce or water (50ml) — this addition is dangerous (violent bubbling and steam). Add from the side of the pan, not directly into the centre. 6. Stir to combine. The caramel will harden slightly when the liquid is added, then re-melt as it continues cooking. 7. Cool. Store in a jar. Decisive moment: The colour at addition of the fish sauce or water. Too pale (light amber): insufficient Maillard products — the caramel will be sweet but lack the bitter-complex depth. Too dark (black): the sugar has burnt and the caramel is irreversibly bitter. Deep amber-brown, just before it begins to smoke: the correct endpoint.
Naomi Duguid & Jeffrey Alford, *Hot Sour Salty Sweet* (2000); Naomi Duguid, *Burma: Rivers of Flavor* (2012)