1 · Pecah minyak
Why the oil has to split
A rempah is mostly water: shallots, garlic, fresh chillies and lemongrass are wet vegetables. While there is water in the pan, the paste cannot get much hotter than 100 °C, so it steams rather than fries, and the sharp raw notes of shallot and garlic stay sharp. Stirring drives the water off. As it goes, the paste thickens and the oil, no longer dispersed in water, gathers at the edges and floats free: pecah minyak, "the oil breaks".
That moment matters because the temperature can now climb past 100 °C into the range where browning begins. Sugars in the shallots caramelise and the Maillard reaction between sugars and amino acids makes the deep, roasted flavours. Push on too far, much above 180 °C, and the paste starts to scorch and turn bitter.
2 · Fat carries flavour
Why so much oil
Many of the flavours in a rempah do not dissolve in water. Capsaicin, the heat in chillies, is almost insoluble in water but dissolves readily in fat; so do the colour of the chillies and turmeric and many of the aroma compounds of lemongrass, galangal and garlic. Frying the paste in oil pulls them out of the plant cells into the fat, and when the stock goes in, the coloured oil carries them through the whole pot. That is why a good laksa has a slick of red oil on top, and why a lean one tastes thin.
Capsaicin also turns to vapour well below its boiling point, from around 115 °C. That is why frying a chilli paste makes everyone in the kitchen cough.
3 · The emulsion
Why the coconut must not boil
Coconut milk is an emulsion: tiny droplets of fat held in water by coconut proteins. Heat changes those proteins. Food scientists at Penn State found that heating coconut milk between 50 and 90 °C made its fat droplets clump together, with some merging above 80 °C, and that heated milk separated more readily. A rolling boil, with its constant agitation, makes it worse. The result is a gravy that looks curdled, with flecks of protein and pools of fat.
In some dishes, rendang among them, that split is the goal. In laksa it is not. Hawkers add the coconut milk late, keep it at a bare simmer and stir it, and 328 Katong Laksa's founder has said the coconut milk must never boil.
4 · Umami
Belacan and dried shrimp
Belacan is made from tiny shrimp, salted, left to ferment, ground and pressed into blocks. Fermentation breaks the shrimp's proteins into free amino acids, glutamate prominent among them, which taste savoury. Toasting the block before use drives off some of the fishiness and adds roasted notes. Dried shrimp contribute more glutamate, and shellfish also carry nucleotides that amplify glutamate's effect when the two meet.
Leslie Tay records that as the cost of dried shrimp rose, some Katong stalls cut back on it, and that the "umami punch" of the gravy faded with it. It is the dried shrimp, more than anything, that makes Katong laksa taste like Katong laksa.
5 · Safety
The trouble with cockles
Blood cockles are filter feeders. They live in coastal mud and concentrate whatever is in the water around them, including viruses from sewage. Traditionally, hawkers shell them raw and dip them in hot gravy for a few seconds, so they stay plump and bloody. That is exactly how Singapore had a series of hepatitis A outbreaks. A 2011 review in the Annals of the Academy of Medicine, Singapore lists seven outbreaks linked to cockles between 1978 and 2002, and names laksa as one of the dishes to which raw shucked cockles are added. It warns that a brief scald will not inactivate the virus, which can survive boiling temperatures for several minutes.
There have been no shellfish-linked outbreaks in Singapore since 2002, and stalls are inspected. But the advice from the Singapore Food Agency is to boil bivalves until they open and then for three to five minutes more, and for pregnant women, young children, older people and anyone with a weakened immune system to avoid raw or undercooked shellfish. At home, cook them through or leave them out.
The four largest cockle-linked outbreaks:
6 · Leaf and sour
Laksa leaf, tamarind and the asam branch
Laksa leaf, Persicaria odorata, is not related to coriander or mint, but it smells a little like both. Its aroma is dominated by long-chain aldehydes, compounds also found in coriander leaf and citrus peel. One analysis of its essential oil found dodecanal at about 44 per cent and decanal at about 28 per cent; a Malaysian study of the closely related Persicaria minor, also sold as daun kesum, found the same two compounds dominant. That is why the leaf goes on raw, at the end: the aldehydes are volatile and fade with cooking.
Asam laksa replaces coconut fat with acid. Tamarind's sourness comes mainly from tartaric acid; asam gelugur, the dried slices of a garcinia fruit used in Penang and Kedah, has a different, sharper sourness of its own. Acid sharpens the fish, cuts its richness, and makes the sweet pineapple and the salty prawn paste on top taste brighter.