Cooking science

Fat as a flavour carrier

A great many aroma compounds dissolve in fat and not in water. Take the fat out of a dish and those flavours have nothing to dissolve in, no way to spread through the food, and no way to be released slowly in the mouth.

Solubility decides where flavour goes

Flavour compounds are broadly either water-soluble or fat-soluble. Salt, sugar, acids and many savoury compounds dissolve in water. A large proportion of aroma compounds — those in spices, herbs, chilli, vanilla and much else — dissolve in fat.

A fat-soluble compound in a watery dish stays where it is. It cannot spread, so the flavour is concentrated in pockets rather than through the whole dish, and much of it is never released at all.

Add fat and those compounds dissolve into it, and the fat carries them everywhere the fat goes.

What this explains

Why spices are bloomed in oil

Their aroma compounds dissolve into the fat and are then distributed through the dish.

Why low-fat versions taste thin

Not only mouthfeel. The flavours literally have less to dissolve in.

Why chilli heat lingers

Capsaicin is fat-soluble, so water does not wash it away. Milk and yoghurt do.

Why vanilla goes into cream

Its compounds dissolve in fat far better than in water.

Why a knob of butter at the end lifts a sauce

It carries aroma and releases it slowly.

Why fat changes the timing of flavour

Fat releases aroma gradually in the mouth, so a fatty dish tastes long and a lean one tastes brief.

Why infused oils work

Chilli oil, garlic oil and herb oils all rely on this.

Using it

• Bloom spices in fat before liquid goes in. Thirty seconds changes a curry completely.
• Fry aromatics in oil, not water. Onion sweated in oil delivers far more than onion boiled.
• Finish with fat. Butter, cream or a good oil stirred in off the heat carries aroma that would otherwise stay put.
• Infuse into fat deliberately — chilli oil, garlic butter, herb oils, a vanilla-infused cream.
• Use the fat you rendered. Duck fat, bacon fat and browned butter all carry flavour from what produced them.
• In a low-fat dish, lean on the water-soluble side — acid, salt, savoury depth, fresh herbs added late.
• Serve dairy with chilli. Milk fat dissolves capsaicin; water does not.

A test worth doing

It takes five minutes and it is convincing.

1. Take a teaspoon of ground cumin and divide it between two small pans.
2. Into the first, add a few tablespoons of water and warm it.
3. Into the second, add a tablespoon of oil and warm it gently for thirty seconds until it smells.
4. Smell both. The oil one is dramatically more aromatic.
5. Add the same quantity of stock to each and taste them side by side.
6. The difference is the whole of this page, and it is why every curry recipe starts with fat.

Common questions