Roast vegetables not browning

The causes, in order

• The tray was too full. Vegetables need space around them so steam can escape. Use two trays rather than one crowded one — this is the fix that works and the one people resist.
• The oven was too cool. Roasting vegetables wants 200–220°C. At 180°C they cook through before they colour.
• Not enough oil. Oil conducts heat to the surface and is what actually browns things. Every piece should be glossy.
• Wet vegetables. Washed and not dried, or straight from the freezer.
• Turned too often. Each turn interrupts the browning that has started. Once or twice at most.
• Salted too early. Salt draws water to the surface. For vegetables that will roast a long time it matters little; for a short roast, season near the end.
• A cold tray. Preheating the tray gives an immediate sear on the underside.

Getting proper colour

1. Cut everything to a similar size, and larger than you think — small pieces dry out before they colour.
2. Dry the vegetables thoroughly.
3. Toss with enough oil that every surface is coated and glossy, not just damp.
4. Preheat the oven to 200–220°C, with the tray in it.
5. Spread the vegetables in a single layer with visible gaps between the pieces. If they touch all round, use another tray.
6. Roast without disturbing them for the first twenty minutes, then turn once.
7. If you are using two trays, swap their shelf positions when you turn them — most ovens are hotter at the top.

By vegetable

Potato, parsnip, carrot, squash

Parboil the potatoes and parsnips; the rest go in raw. 200–220°C, 35–50 minutes.

Brassicas — broccoli, cauliflower, sprouts

High heat, shorter time. They char beautifully and go bitter and sulphurous if slow-cooked.

Onions and peppers

Release a lot of water. Give them extra space and high heat.

Courgette and aubergine

Very wet. Salt and drain first, or roast at a high heat on a preheated tray.

Tomatoes

Slow-roast at 140°C for concentrated flavour, or blast at 220°C for blistering. The middle range gives neither.

Mushrooms

The wettest of all. Very hot oven, plenty of space, no salt until the end.

Why crowding is the whole problem

Vegetables are mostly water, and that water has to leave before anything can brown. As long as there is liquid at the surface, the surface cannot rise above 100C, and browning reactions need considerably more than that.

On a crowded tray the water released by each piece has nowhere to go. It fills the space between them as steam, keeps every surface damp, and the tray becomes a closed humid box. The vegetables cook through perfectly well; they simply never get the chance to brown.

Spread out, the same water evaporates into moving oven air and disappears. The surfaces dry, climb well past 100C, and the browning that produces most of the flavour can finally start. This is why two half-full trays beat one full one so decisively, and why it is worth the extra washing up.

Common questions