Cooking science

Crowding suppresses evaporation

Put too much in a pan and the food steams rather than browns. It is the commonest reason home cooking looks and tastes different from restaurant cooking, and it is entirely a matter of physics rather than skill.

What happens in a full pan

Food releases water as it heats. In a pan with space around each piece, that water evaporates immediately, the surface dries, and once dry it can rise above the boiling point of water and begin to brown.

In a crowded pan the water has nowhere to go. It fills the space above the food as steam, the surfaces stay wet, and a wet surface cannot exceed 100°C no matter how hot the hob is. Browning cannot begin until the water has gone, and in a crowded pan it never quite does.

Worse, all that cold food dropped in at once pulls the pan temperature down sharply, and a cool pan releases more water still. The pan spends several minutes recovering, by which time the food has been simmering in its own juices.

How to recognise it

• You hear a dull bubbling rather than a sustained sizzle. Sound is the most reliable early signal.
• Visible liquid pooling in the pan.
• Food turning grey or pale rather than brown.
• Vegetables collapsing and going limp rather than catching at the edges.
• Steam billowing from the pan rather than the food.
• Mushrooms are the extreme case — crowded, they release enough water to poach themselves.

What to do about it

• Cook in batches. Tedious and correct. Two batches take a few minutes longer and produce something entirely different.
• Use a bigger pan. The cheapest fix, if you own one. Surface area is what you are buying.
• Get the pan properly hot before anything goes in. More stored heat means faster recovery.
• Dry the food first. Patting meat and vegetables dry removes surface water that would otherwise have to boil off.
• Do not stir constantly. Every stir exposes wet surfaces and interrupts the browning that is starting.
• Salt at the end, for anything you want browned. Salt draws water out at exactly the wrong moment.
• Accept it and change dish. A crowded pan of vegetables makes a decent braise. Add liquid deliberately and call it what it is.

Where it matters most

Searing meat

The clearest case. Crowded steak or mince goes grey and never develops a crust.

Mushrooms

They are mostly water. Give them room and high heat, or they stew.

Stir-frying

A domestic hob has a fraction of the power of a restaurant one, so batches matter more, not less.

Roasting vegetables

A crowded tray steams. Use two trays, and swap shelves halfway.

Deep-frying

Too much at once drops the oil temperature, and cool oil is absorbed rather than repelled. This is exactly why fried food goes greasy.

Onions for a base

Here crowding is sometimes useful — a covered, crowded pan sweats onions soft without colour, which is what some dishes want.

Common questions