Cooking science

Surface drying

Almost every complaint about food not browning — grey steak, flabby chicken skin, pale roast potatoes, soggy vegetables — comes down to the same thing. The surface was wet, and a wet surface cannot get hot enough to brown.

Water holds the surface at boiling point

While there is liquid water on a surface, essentially all the energy arriving goes into turning that water into steam rather than into raising the temperature. The surface sits at around the boiling point of water and stays there until the water has gone.

The browning reactions — Maillard and caramelisation — need considerably more than that. So nothing browns until the surface has dried, and every second spent boiling off surface moisture is a second the food is cooking through without colouring.

This is why the same steak in the same pan can come out grey or deeply crusted depending on nothing more than whether it was patted dry.

Where it shows up

• Grey steak. A wet surface, or a pan too cool to evaporate the moisture quickly.
• Flabby chicken or pork skin. Skin holds a great deal of water and it has to leave before the skin can crisp.
• Pale roast potatoes. Not drained and steamed dry before they went into the fat.
• Vegetables that steam rather than roast. Washed and not dried, or crowded so the released water cannot escape.
• Grey mushrooms. They release their own water faster than a crowded pan can evaporate it.
• Fish that sticks and tears. A wet fillet steams onto the pan rather than searing and releasing.
• Batter that slides off. The coating cannot grip a wet surface.

What to do about it

Almost all of this is the same three actions.

1. Pat the surface dry with kitchen paper, and do it again immediately before cooking. Moisture reappears.
2. For skin, salt it and leave it uncovered in the fridge for a few hours or overnight. Air-drying does more than any other single step.
3. Get the pan or the oven genuinely hot, so what moisture there is evaporates quickly rather than pooling.
4. Do not crowd the pan or the tray. Released water has to have somewhere to go.
5. Do not cover anything you want to brown. A lid returns every drop of moisture to the surface.
6. Salt at the right moment: well ahead so it can draw moisture out and be blotted, or immediately before. Ten minutes ahead is the worst timing.

The related principles

Evaporation

The process itself, and where the energy goes.

Crowding suppresses evaporation

Why a full pan behaves differently from a half-empty one.

Maillard reaction

What happens once the surface is dry and hot enough.

Crust formation

The structure that results.

Osmotic moisture movement

How salt draws water to the surface in the first place.

Drying a surface deliberately

Where browning or crisping is the point, drying the surface is a step rather than an accident, and it is the step most often skipped.

1. Pat dry with kitchen paper. This alone accounts for most of the difference in a domestic kitchen.
2. Leave it uncovered in the fridge, on a rack, for a few hours or overnight. Refrigerator air is dry and it draws moisture out steadily.
3. Salt it first for meat and fish, which draws water to the surface where it can evaporate, and season it at the same time.
4. Give it airflow. A rack rather than a plate, so the underside dries too.
5. For duck and chicken skin, this is the whole technique — a dry skin crisps and a damp one steams.
6. For a sear, dry the surface again immediately before it goes in the pan, because it will have wept.
7. For roast potatoes, let the steam escape after draining, then let them sit for a minute before they go into the fat.

Common questions