What a Thai curry paste really is

A Thai curry paste is not a sauce you spoon straight from the jar. It is a concentrated seasoning base — a pounded mixture of chillies, aromatics and salty ingredients — designed to be fried briefly in coconut cream before any liquid goes into the pan. That short fry, often called "cracking" the coconut cream, is where most of the flavour comes from. Skip it and you will end up with a thin, flat curry that tastes of raw garlic and shrimp paste.

The core ingredients rarely change much: fresh or dried chillies, lemongrass, galangal (a sharper, piney cousin of ginger), makrut lime zest, garlic, shallots, coriander root, shrimp paste, salt and sometimes a little sugar or dried spice. What changes between pastes is the type and proportion of chilli, and the extra aromatics folded in around it.

Red, green and yellow: the practical differences

Colour tells you a fair amount, though it is not a strict heat scale.

• Green paste is built on fresh green bird's eye chillies, with plenty of coriander root, basil and sometimes green peppercorns. It is usually the hottest of the three, but the heat is bright and herbal rather than dark. It suits chicken, fish, prawns and vegetables, and works beautifully in a quick weeknight curry.
• Red paste uses dried red chillies that have been soaked, plus dried spices such as coriander seed and cumin. The result is deeper and earthier, with a slower, rounder heat. It is the natural partner for beef, pork, duck and richer coconut curries.
• Yellow paste leans on turmeric, which gives both its colour and a warm, slightly bitter edge. It is generally the mildest of the three, fragrant and gently spiced. It works well with fish, chicken, potatoes and squash, and is the paste most people reach for when cooking for children or spice-averse guests.

Two close relatives are worth knowing. Massaman paste is spice-heavy and gently sweet, influenced by Persian and Indian cooking; panang is a red-style paste with ground peanuts, richer and thicker. Both behave differently in the pan, so treat them as their own thing rather than red paste with extras.

Buying pastes in the UK

Supermarket shelves have improved enormously, but not all jars are equal. Read the ingredients list rather than the picture on the front. A decent paste will list chillies, lemongrass, galangal, garlic, shallots and shrimp paste near the top. If water, sugar or sunflower oil come first, you are essentially buying a ready-made sauce, which is fine but needs different treatment — less frying, more tasting.

Pastes sold in small plastic tubs from Asian grocers are often fresher and punchier than long-life jars. Vegetarian versions swap shrimp paste for fermented soy or salt, and they work well, though the flavour is a little less rounded. Sachets are convenient but rarely the best value.

Storing paste so it keeps its punch

Paste is a living, aromatic thing. It fades fast once opened, so treat it with a bit of care.

• Keep it in an airtight container in the fridge, not the door, and press a thin film of oil over the surface to slow oxidation.
• Always use a clean, dry spoon. A wet spoon introduces water and shortens its life dramatically.
• Opened jars or tubs keep for several weeks in the fridge; homemade paste is best used within a fortnight.
• For longer storage, spoon paste into an ice cube tray, freeze, then bag the cubes. One cube is roughly a tablespoon — ideal for a single curry.
• Trust your nose. If it smells sour, musty or oddly sweet, bin it.

When it is worth making your own

Making paste from scratch is not a daily habit, but it is worth doing once. Do it when you have a good Asian grocer nearby, forty minutes to spare, and a curiosity about how the flavours fit together. You will notice the difference most in green curry, where freshness really shows.

You will need dried chillies (soaked in hot water for twenty minutes), lemongrass (only the tender lower stem), galangal, makrut lime zest, garlic, shallots, coriander root or stems, shrimp paste, salt and a little palm sugar. Toast any dried spices first. Pound the fibrous ingredients — lemongrass, galangal, lime zest — before the softer ones if using a mortar. A blender works fine with a splash of water, though the texture will be slightly looser.

Make a double batch and freeze it in cubes. The effort is front-loaded, and you will be grateful on a Tuesday night.

Getting the balance right in the pan

Start with one to two tablespoons of paste per 400ml tin of coconut milk. Spoon the thick cream from the top of the tin into a hot pan first, fry the paste in it for a minute or two until it smells fragrant and the oil separates, then add the rest of the milk and your protein or vegetables. Finish with fish sauce for salt, a little palm sugar for roundness and lime juice for lift. Taste before serving — pastes vary wildly in salt and heat, and no recipe can account for that. Adjust, and you will be cooking Thai food rather than simply following it.