Many classic sauces, like veal demi-glace, rely on long, slow simmering to develop their intense flavors and lip-smacking viscosity. These complicated sauces may have fallen out of fashion, but the technique—reduction—is useful in modern saucemaking. As a sauce simmers, the water evaporates, creating a more concentrated, somewhat thicker sauce. Here are some tips for better reductions.
• Flavors become more intense when reduced so it’s vital to begin with good-tasting ingredients. For example, an unpleasant wine will taste even worse when reduced.
• Heavy cream can be reduced by about half its volume, creating an incredibly unctuous, rich sauce base (reducing by more than half can make the cream separate). Add cream to a deglazing liquid in a sauce and then reduce, or reduce it on its own and then add it to a sauce.
• Salt gets more concentrated when water evaporates, so avoid using canned stocks, which are often very salty.
• Multiple reductions create layers of flavors. For example, a deeply flavored sauce may be made by first reducing the wine used to deglaze a pan, adding some stock and reducing it, and finally adding cream and reducing once more.
• For the best flavor, reduce liquids at a steady simmer or a gentle boil so that some of the sauce splatters onto the sides of the pan, where it can caramelize. Stir the sauce occasionally to dissolve these caramelized bits back into the sauce.