Pots for dum biryani: deg, degchi, handi and lagan

Dum (dum pukht) is slow cooking in a heavy-bottomed pot, sealed so the steam stays in. The lid is closed with a rope of dough, and the food cooks in its own juices over low heat.

So the pot needs three things: a thick base that will not scorch the bottom layer, a lid that sits flat on the rim, and a body large enough to leave headroom for steam.

• Deg: a large, heavy cooking pot, the caterer's and community kitchen's biryani vessel.
• Degchi: a smaller deg, for a home or a restaurant's daily batches. In English, a stock pot or cooking pot.
• Handi: a round-bellied pot with a broad mouth, the classic pot for sealing with dough. Small handis also carry biryani to the table.
• Lagan: a wide, shallow pan, used for dum dishes that are cooked and served in the same vessel.

Copper conducts heat about four times better than brass, so it heats evenly and answers the flame quickly: fewer scorched bottoms on a long dum.

Brass is heavier for the same size and costs less by weight. Its weight holds heat steadily, which is why the trade uses it for big degs and topes.

Either way, compare weight for size between sellers: a heavier pot has thicker walls.

Biryani marinades carry curd, lemon and tomato, all sour, so a brass or copper biryani pot must be tinned inside. India's food regulator treats untinned brass and copper food containers as unfit for food.

Tin melts at about 232 °C. Never heat a tinned pot empty, and keep the flame low once the dum seal is on. Re-tin when yellow or red metal shows through.

Choose by the largest batch you cook, not the average. A caterer usually keeps a run of graded sizes, and reorders the same codes.

Ask for the capacity in litres and the weight of each size, whether the lid is included, and how the handles or rings are fixed: a full deg is heavy.

• Soak off the dough seal with warm water; do not scrape the tin.
• Wash with mild soap, rinse and dry at once, inside and out.
• Polish the outside now and then; the inside needs only washing.