Nappe

Nappe, from the French napper, "to coat", describes a sauce that is thick enough to cling to food in a thin, even layer. In practice it means the sauce coats the back of a spoon. It is the target thickness for custard sauce, many cream sauces and reduced stocks.

How to do it

1. Dip a metal or wooden spoon into the sauce and lift it out.
2. Turn the spoon over and look at the back. The sauce should cover it in an even, opaque layer, not run off.
3. Draw a finger across the back of the spoon.
4. If the line stays clean and the sauce on either side does not run back into it, the sauce is at nappe.
5. If the line fills in, keep cooking or reducing. If the sauce is gloopy and clumps, thin it with a little liquid.

How to tell it is done

For custard sauce, crème anglaise, nappe comes at about 77 to 82°C (170 to 180°F). A thermometer helps, because above that range the yolks start to scramble. For a béchamel or a reduced stock, there is no exact temperature; use the spoon test.

Why it works

A sauce thickens when starch swells, egg proteins set, or liquid evaporates and leaves more gelatin behind. The spoon test is a quick way to check thickness while the sauce is hot. Most sauces thicken more as they cool, so nappe when hot gives a good texture at the table.

Common mistakes

• Testing with a cold spoon in a gelatin-rich sauce, which sets the sauce on contact and fools you.
• Overshooting a custard while waiting for it to look thick. Take it off the heat as soon as the line holds.
• Testing on the front of the spoon, where the sauce pools.

In recipes

You will see "cook until nappe", "until it coats the back of a spoon" or "until it naps the spoon". All mean the same test.