Cooking in
South Australia
Thai
Tom Yam (Hot and Sour Soup)
A clear or slightly cloudy hot and sour soup — the preparation that many outside Thailand take as the defining flavour of Thai cooking, and that Thai cooks take as the demonstration of the country's most fundamental flavour philosophy. Tom yam is not a recipe but a principle: a hot broth intensely flavoured with lemongrass, galangal, kaffir lime leaves, chilli, and fish sauce, soured with lime at the last moment, with the protein (typically prawns — tom yam kung) added only seconds before service. Every element except the broth is added at different temperatures: the aromatics infused in hot stock; the chilli providing heat that builds; the lime juice added off heat, cold, for its fresh aromatic character; the fresh herbs (coriander leaf) scattered at the last moment. The preparation is assembled, not cooked.
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Cook
I
The Market List
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For the prawn stock
shells and heads from 400 g prawns
prawn shells and heads
briefly sautéed in oil, then simmered in water for 20 minutes
1 litre
water
Your own market
8
lemongrass stalks
bruised hard with the flat of a cleaver blade, cut into 4–5 cm pieces
Origin · Thailand
30 g
galangal
peeled, thinly sliced
8
kaffir lime leaves
torn roughly
12–20
bird's eye chillies (phrik khi nu)
split lengthwise, seeds retained; quantity to heat preference
400 g
raw prawns
shelled and deveined, shells and heads reserved for stock
Your own market
30 ml
fish sauce
to season; adjust at finish
Your own market
5 g
palm sugar
a small quantity only
Origin · Indonesia
60 ml
lime juice
freshly squeezed; added off heat at the last moment, generously
Your own market
120 g
oyster mushrooms or straw mushrooms
optional; added off heat with the lime juice
Your own market
15 g
coriander leaf
scattered at service
For tom yam nam khon (the richer, slightly cloudy version)
2 tbsp
nam prik pao (roasted chilli paste)
see Entry T-16; omit for the clear, more immediately aromatic version
II
The Method
1
Sauté the prawn shells and heads briefly in a little oil over high heat until they turn pink and fragrant, so the dry heat draws colour and roasted depth from the shells before the water ever touches them. Add 1 litre of water and simmer for 20 minutes, then strain. The stock is ready when it tastes clearly of prawn — the aromatics will intensify a good stock, but they cannot create one from nothing.
2
Bring the prawn stock to a gentle simmer in a wide saucepan and add the bruised lemongrass, sliced galangal, and torn kaffir lime leaves, bruising and tearing them so their volatile oils bleed into the broth rather than staying locked inside. Simmer for 2–3 minutes. After 2 minutes, test by smell: the broth must carry an intense, citrus-green character of lemongrass and kaffir lime — a faint smell tells you the lemongrass was not bruised hard enough.
3
Add the fish sauce and palm sugar, stirring until the sugar has dissolved so it integrates evenly rather than sitting in a sweet patch at the bottom. Add the split chillies, splitting them so the seeds are exposed to the broth and the heat builds fully. The broth now carries its complete seasoning base.
From the canon — Fish sauce — nam pla — is the universal salt of the Thai kitchen. Fish Sauce (Nam Pla): Selection and Use →
4
Add the prawns and cook in the hot broth for 60–90 seconds only, watching the shape rather than the clock — the prawn is done when it has turned fully opaque and curled into a 'C', not a tight 'O', which tells you it has gone a breath too far. Remove the pan from the heat the instant the prawns reach this point, since they will continue to cook in the residual heat of the broth.
5
This is where the dish lives or dies. With the pan entirely off the heat, add the lime juice immediately before serving, so the volatile aromatic oils that give tom yam its vivid citrus lift are not driven off by heat — the acid survives, but the freshness does not, and a soup finished over heat or left to rest after the lime goes in will taste merely sour rather than sour and alive. Taste at once: the dominant note must be sour, the secondary hot, the third savoury; adjust with more fish sauce for salt, more lime for sour, or a pinch of palm sugar if the acidity is too sharp, then stir in the nam prik pao and add the mushrooms.
6
Ladle immediately into warmed bowls, leaving the lemongrass and galangal pieces in the soup so they continue to release aroma into the hot liquid at the table — they are moved aside when eating, not removed before service. Scatter coriander leaf over each bowl and serve at once.
III
Quality Hierarchy
01
Reserve — Stock made from the shells and heads of wild-caught prawns with genuine depth of flavour; lime juice pressed from fresh kaffir limes or highly aromatic Persian limes; lemongrass cut to order from living plants; nam prik pao made in-house to Entry T-16.
02
Estate — Stock made from fresh farmed prawn shells sautéed and simmered to order; fresh lemongrass with firm, moist hearts; kaffir lime leaves from a live plant or vacuum-packed fresh; freshly pressed lime juice.
03
Market — A well-made light chicken stock in place of prawn stock; supermarket lemongrass checked for firmness; kaffir lime leaves fresh or frozen (not dried); a reliable commercial nam prik pao.
04
House — Commercial liquid stock — the point at which the preparation loses its foundation; the aromatics can perform only as well as the medium into which they infuse, and a stock without character produces a soup without character.
IV
Sensory Tests
◇Smell. After 2–3 minutes of simmering with the aromatics, the broth carries an intense, vivid citrus-green scent of lemongrass and kaffir lime; a faint smell means the lemongrass was insufficiently bruised or too old.
◇Sight. The prawn has turned fully opaque and curled to a 'C' shape; a tight 'O' curl means it is overcooked.
◇Touch. The lemongrass stalk, when struck with the flat of a cleaver blade, yields and softens slightly without fully separating — the cell walls are broken and the citral released.
◇Where it lives or dies. Lime juice must be added off heat, in generous quantity, in the final seconds before the bowl reaches the table — heated lime loses its volatile aromatic oils almost instantly, and a tom yam finished any earlier tastes sour but not fresh.
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VI
What to Pour
The pairing
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