Cooking science

Volatile generation

The tongue detects five tastes. Everything else that you experience as flavour — the difference between a roast chicken and a boiled one, between fresh and dried herbs, between raw and caramelised onion — reaches you through the nose, as volatile compounds evaporating from the food.

Taste and flavour are different things

Taste is what the tongue reports: sweet, salt, sour, bitter and savoury. That is the whole list. Everything else — fruity, nutty, floral, roasted, green, meaty, smoky — is smell, detected by receptors at the top of the nose, both from sniffing and from vapour rising up the back of the throat as you chew.

This is why food tastes of almost nothing with a heavy cold, and it is why a dish that seems flat may not need more salt at all — it may need more aroma, from herbs, spices, browning, acid or fat.

Where cooking aromas come from

Browning reactions

The Maillard reaction and caramelisation between them generate hundreds of aroma compounds that were not in the raw food at all. This is the largest single source.

Fat breakdown

Fats degrade with heat into aromatic fragments, which is why roast and fried food smells different from boiled, and why lamb, beef and pork smell distinct — much of it is in the fat.

Plant cell damage

Cutting garlic, onion, basil or mustard triggers enzymes that produce aroma compounds within seconds. Nothing smells of garlic until it is cut.

Fermentation

Yeasts and bacteria produce large quantities of aromatic compounds, which is most of what distinguishes bread, cheese, soy sauce and wine.

Existing volatiles released

Herbs, spices and citrus zest carry aroma in oil-filled structures, released by bruising, grating or warming.

Why fat and heat matter

Most aroma compounds dissolve far better in fat than in water. Fat therefore collects them, holds them, and releases them gradually as you eat — which is a large part of why fat-free food tastes thin, and why frying spices in oil at the start of a dish extracts so much more than adding them to a watery sauce later.

Heat drives volatiles into the air. That is useful when you want to smell food, and a loss when it happens too early: delicate herbs, citrus zest and freshly ground spice lose their character within minutes of hitting a hot pan. Robust aromatics go in at the beginning, delicate ones at the end. This one rule explains most of what recipes mean by "stir in the coriander just before serving".

Practical consequences

• Bloom whole spices in hot fat at the start. It extracts far more than simmering them in liquid.
• Add soft herbs, zest and fresh chilli at the very end. Add bay, rosemary, thyme and dried spice early.
• A lid keeps volatiles in the pot; cooking uncovered sends them into the room. Both are sometimes what you want.
• Grind spices as you need them. Pre-ground spice has been losing aroma since the day it was ground.
• Serve food warm rather than hot or cold. Very cold food releases almost no aroma, which is why ice cream is over-sweetened and why cheese should come out of the fridge early.
• If a dish tastes flat, try acid, fat or fresh aromatics before reaching for more salt.

Common questions