Why Duck Needs Acidity: A Kitchen View

Key facts

Where the fat comes from

a layer under the skin of a waterfowl

What acidity does

makes the mouth water, clears fat from the tongue

Chinese kitchen

plum sauce, sweet-sour dips

Thai kitchen

pineapple, lychee, tomato in roast duck red curry

French kitchen

duck à l'orange, bitter-orange (bigarade) sauce

The fat under the skin is the kitchen’s problem

Ducks live on water, so they store a thick layer of fat under the skin against the cold. Roasting renders some of it out; the rest stays in the skin and meat.

Fat gives roundness and aroma, but it coats the tongue and palate. After a few bites the tongue picks up less flavour and the dish feels heavier and heavier.

The problem is sharper in Thai-Chinese cooking, where roast duck is often brushed with honey or sugar. Sweetness on top of fat turns cloying faster than plain roasted meat.

A kitchen has two answers. Cook the bird long enough to render the fat, and put something sour on the plate.

Sweet-sour sauces and fruit: the Thai, Chinese and French answer

Kitchens that never swapped recipes reached the same answer: duck with something sour and slightly sweet.

• Chinese: roast duck and Peking duck often come with plum sauce or a sweet-sour sauce
• Thai: red curry with roast duck carries pineapple, lychee or tomato, and braised duck often comes with a sour chilli-vinegar dip
• French: duck à l'orange is roast duck with bigarade sauce, originally made from bitter Seville oranges with sugar and vinegar

All three use a little sweetness to carry the sourness. The sugar makes the sauce easy to take; the acid does the work on the fat.

Acidity in wine does the same job

Wine carries natural acids from the grape, mainly tartaric and malic acid. On the tongue they act much as lime or orange juice does.

When a high-acid wine follows a bite of duck, saliva rises and washes away the coating of fat, so the next bite reads as clearly as the first. A low-acid wine only adds weight.

That is why cool-climate wines suit duck. Grapes that ripen slowly in cool weather hold on to more acid than grapes from hot regions, so a light red such as Pinot Noir or a white such as Riesling follows the same logic as the sauce.

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