Coconut milk in curries

Why

Coconut milk is an emulsion of coconut fat droplets in water, held together by coconut proteins; when the can stands, the cream with the fat rises to the top. Longer heating alters the proteins and the droplets start to cluster, and with hard boiling and evaporation of water the emulsion breaks: the fat separates on the surface and the rest turns grainy. Traditional Thai curry does this on purpose, cooking down the thick coconut cream until it releases its oil and frying the curry paste in it, so the aromatic compounds of the spices dissolve in the fat (Blooming spices in fat card). Many shop-bought coconut milks, however, contain emulsifiers and stabilisers, so the oil separates poorly or not at all, and light coconut milk is simply more diluted. For a smooth, creamy sauce the coconut milk is therefore only heated through without hard boiling, and lime or tamarind go in towards the end mainly for their fresh taste; coconut proteins only cluster in strongly acidic conditions, which a curry does not normally reach.

How to do it

• For a Thai-style curry don't shake the can: cook the thick cream from the top layer, stirring constantly, until it thickens and the oil separates, and fry the paste in it.
• If the oil won't separate, add a spoonful of neutral oil and fry the paste in that; stabilised coconut milk may not split at all.
• Add the rest of the coconut milk after frying the paste and keep cooking gently, just so the surface bubbles.
• For a smooth, creamy sauce stir the coconut milk in the can first and only heat it through in the pan, without hard boiling.
• Add lime juice or tamarind towards the end, a little at a time, and adjust the salt with fish sauce at the end as well.

If it goes wrong

Oil on the surface of a Thai curry is fine; if it bothers you, skim it off with a spoon, or off the heat stir it back in with a few spoonfuls of cold coconut milk. A grainy, broken sauce after long hard boiling will not fully come back together; a brief whizz with an immersion blender may make it a little smoother, and next time keep only a gentle simmer after adding the coconut milk. Reduce a thin curry uncovered, or thicken it with a little coconut cream.