Roasted vegetables

Why

Vegetables contain a lot of water, and as long as it is evaporating from the surface, the surface stays at around 100 °C, where it does not brown; browning and caramelisation of sugars only come once the surface dries. A crowded tray is therefore a trap: the steam between the pieces has nowhere to go and the vegetables stew in it, while pieces in a single layer with gaps lose their steam quickly and begin to roast. A hot oven of about 200–230 °C and a thin coat of oil heat and dry the surface evenly; just enough oil to make the vegetables shine is plenty, more only soaks in and makes them greasy. The size of the pieces decides whether the centre cooks before the edges turn black: large chunks of dense roots need longer, small, watery pieces can take short, fierce heat. In starchy foods, mainly potatoes and roasted root vegetables, acrylamide forms when cooking above 120 °C, which is why the UK FSA advises roasting them to golden yellow, not dark brown.

How to do it

• Cut the vegetables so they cook at the same time: dense roots into smaller pieces, soft and watery vegetables into larger ones.
• Pat the pieces dry and toss them with just enough oil to make them shine; salt them just before roasting.
• Spread them on the tray in a single layer with gaps; if they don't fit, use two trays.
• Roast in a preheated oven at about 200–230 °C and turn the pieces halfway through.
• Roast potatoes and root vegetables to golden yellow, not dark brown.
• Peppers and aubergines that you want to peel, on the other hand, roast in a hot oven until the skin blackens, then cover them so the skin steams loose and slips off easily.

If it goes wrong

Drain pale, stewed vegetables of their liquid, spread them over more trays and keep roasting in a hot oven until they start to brown. Burnt edges with a raw centre mean the pieces were too big or the oven too hot: finish the vegetables at a lower temperature covered with foil and cut smaller pieces next time. Let greasy vegetables drain on paper towels.