Ingredient

Duck fat

Duck fat is soft, savoury and stays liquid at a lower temperature than most animal fats, which is why it coats a potato so evenly and crisps it so well. If you ever cook duck breasts you already have more of it than you realise.

Why it works so well on potatoes

A roast potato crisps when the surface starch dries and browns. That requires the fat to coat the whole surface evenly and to stay hot without burning.

Duck fat is softer than beef dripping and lard, so it clings and spreads readily even on a chilled potato. It also carries a savoury, faintly gamey flavour that reads as depth rather than as duck.

Goose fat behaves almost identically and is used interchangeably. Both are expensive to buy in a jar and effectively free if you render your own.

Collecting and keeping it

1. Cook duck breasts skin side down from a cold pan and pour off the fat as it renders. One breast gives a surprising amount.
2. Roasting a whole duck or a set of legs gives more still — pour it off the tin while hot.
3. Strain it through a fine sieve or a piece of muslin to remove solids, which are what make stored fat go off.
4. Pour into a clean jar and let it set. It should be pale, creamy and smooth.
5. Keep it in the fridge. Store it apart from the meat juices, which separate out underneath and are worth keeping for gravy but not for frying.
6. Top up the same jar as you accumulate more, provided each addition has been strained.

What to do with it

• Roast potatoes. Parboil, rough up the edges, and roast in very hot duck fat. This is the reason most people have it.
• Confit. Duck legs cooked slowly submerged in fat, then crisped. It needs a lot of fat and the fat is reusable afterwards.
• Roast root vegetables — parsnips, carrots, celeriac — where it does the same job as on potatoes.
• Fried eggs and fried bread, which is an extravagance and a good one.
• Sautéed potatoes and pommes sarladaises, sliced and fried with garlic and parsley.
• Starting a cassoulet or a bean dish, where it gives depth from the beginning.
• Rubbed over a bird before roasting, particularly a lean one.

Duck fat, goose fat and the others

Duck fat

Soft, savoury, faintly gamey. Melts easily. The general-purpose luxury roasting fat.

Goose fat

Very similar, slightly milder and softer still. Traditionally the Christmas potato fat.

Beef dripping

Firmer, stronger, beefier. Excellent for chips and roast potatoes, and a different flavour.

Lard

Firm, mild, cheap. Very good and less characterful.

Reusing

Fat used for confit can be strained and reused repeatedly. Fat used at high roasting heat degrades faster.

Common questions