Reduce

To reduce is to cook a liquid uncovered so some of its water evaporates. The liquid gets smaller in volume, thicker, and stronger in flavor. Cooks reduce stock, wine, cream, juices and sauces. A sauce made this way is often called a reduction, and it is the core of a pan sauce and of demi-glace.

How to do it

1. Use a wide pan. A larger surface lets water evaporate faster.
2. Bring the liquid to a steady simmer or a gentle boil, uncovered.
3. Stir now and then, and scrape down the sides so nothing burns there.
4. Skim off foam or fat that rises.
5. Check the amount. To judge "reduce by half", note the level on the pan before you start, or dip a wooden spoon at the start and mark it.
6. Season only at the end. Salt gets stronger as the water leaves.

How to tell it is done

The liquid has dropped to the amount the recipe asks for. A sauce reduced enough will coat the back of a spoon: run a finger through the film and the line stays clear. This look is called nappe. Bubbles get larger and slower as a sauce thickens.

Why it works

Heat turns water into steam, while sugars, salts, gelatin and flavor compounds stay behind. The same flavor ends up in less liquid. Gelatin from good stock and sugars from wine or juice make the liquid thicker as they concentrate.

Common mistakes

• Salting first. A well-salted stock reduced to a quarter will be far too salty.
• Covering the pan. Steam cannot escape and nothing reduces.
• Too much heat at the end. As sauces thicken they catch and burn quickly.
• Reducing milk or cream on high heat. It boils over or scorches. Keep it gentle.
• Reducing poor stock. Store-bought stock without gelatin will get salty before it gets thick.

In recipes

"Reduce by half" means until half the starting volume is left. "Reduce until syrupy" means until it coats a spoon and bubbles slowly. "Reduce to a glaze" means almost all the water is gone and the liquid is sticky. You often deglaze a pan with wine and then reduce it.