A reduction sauce can be anything from a rich, complex veal demi-glace to a quick, delicious sauce that you make from the bits left in the pan after you sauté a couple of steaks. Indeed, many fine sauces owe their marvelous complex taste and silky body to this basic technique: classic stock-based sauces such as chasseur and bordelaise, red- and whitewine sauces, and many cream sauces. Even sauces that get their body through means other than reducing, like a béchamel (which is thickened with a roux), gain in flavor when simmered a bit to concentrate and transform their ingredients.
Reducing, which happens through simmering or boiling, removes water by evaporation, and therefore concentrates and intensifies flavors, but less water is only one of the reasons that reduced liquids taste good. Some acids and other strong-tasting compounds have low boiling points and are actually boiled off, enhancing the flavor of the remaining liquid by their removal. Not only are some unpleasant-tasting compounds removed, some potential problem ingredients are removed, too. For example, when you reduce wine, tannins and other compounds that might cause any cream in the sauce to curdle are boiled off, eliminating the risk.
Even more changes take place as your liquid simmers away. The high heat speeds up chemical reactions, and some compounds in the sauce break apart while others join together, creating new compounds that have totally different flavors.
During the reduction, the liquid boils and some is spattered on the pan just above the sauce level. As the sauce reduces, some particles of dried sauce are left on the pan. This dried sauce gets quite hot since it isn’t protected by liquid. The sauce contains both proteins and sugars from the meat, wine, and stock. At this higher heat, complex browning reactions (called Maillard reactions) take place with the protein and sugars. Many of the same wonderful sweet compounds that form when sugar is caramelized are produced. Then, when you stir and splash the sauce back on these dried compounds, many of these are redissolved in the-sauce.
Repeat the reduction to deepen the flavors
The flavors of your final sauce will of course be determined by how much you reduce the ingredients, but also by when each ingredient is reduced—a sauce made by reducing wine, adding stock and reducing it, and then adding cream and reducing that will taste much different than one made by combining wine, stock, and cream and reducing them all together.
Some chefs even use multiple reductions of the same ingredient to get very complex layers of flavor. For example, a classic French jus (an intensely flavored, fairly light-bodied sauce) is made from repeated reductions of a small amount of stock added to a mirepoix and browned bones. You add the stock, cook it dry (taking care not to let it burn), add more stock, cook it dry again, repeating the process until the liquid is very flavorful. Each time you cook the pan dry, you allow the mirepoix and bones and glazy liquid to deepen in flavor. Then each time you add more stock, you dissolve the wonderful brown sweet compounds that were created. This sauce will taste entirely different (and much better, I think) than the same amount of stock added to the bones and mirepoix and just reduced slowly in one go.
These same principles apply to sauces that are an integral part of a dish, as in braises and stews. Louisiana chef Paul Prudhomme has an interesting technique that he calls “cooking on the bottom of the pan.” To make a gumbo, he will start with a little fat and some chopped onions, celery, peppers, and okra in his pan. He adds a cup or so of stock and reduces until the vegetables just start to stick and brown on the bottom. Then he adds another cup of stock, scrapes the bottom well to loosen the browned, cooked-on pieces, and then reduces again. He does this several times. This process cooks the vegetables, but more important, it produces wonderful, sweet browned compounds that give the finished gumbo a deep, complex flavor.
How to make a quick reduction sauce
Here’s one way to make a quick and delicious reduction sauce: Start by deglazing the skillet after you sauté seasoned pieces of meat (beef, pork, veal, lamb) in a little fat in a skillet. When the meat is cooked, transfer it to a plate and keep it warm. Pour off the fat, add red or white wine (or other flavorful alcohol, such as Cognac or Calvados) to the skillet, and simmer the liquid, scraping the pan to loosen any stuck-on meat particles, until there are just a few tablespoons of syrupy liquid left. Next add a little stock and reduce again until the liquid is intensely flavored and slightly syrupy. Finally, add a little cream or crème fraîche and reduce until the sauce thickens slightly. You have only to taste, add seasonings as needed, and spoon a wonderful hot sauce over the meat. In a medium to large heavy skillet, over high heat, the whole process takes only a few minutes.
Tips for successful reduction sauces
• If you’re using wine in the sauce, be sure to use a decent quality one, something that you’d drink with the meal you’re making, if possible. And definitely don’t use “cooking wine,” which is very poor quality wine that contains salt.
• Don’t try making a reduction sauce with regular canned stock: it’s generally quite salty to begin with and when reduced will be too highly salted. Homemade stock is best, if you have it, or try a low-sodium prepared stock.
• If you plan to finish the sauce with cream, be sure that any wine or other alcohol has been sufficiently cooked off before adding the cream, to prevent curdling.
• Once a reduction sauce is finished, don’t try holding it over low heat because it will continue to reduce slowly. Instead, take it off the heat and reheat gently just before serving. This is especially important if the sauce was finished with cream or butter: the emulsion that was formed between the liquids and the fat in the cream or butter can break if not enough liquid remains to go between the droplets of fat. Free fat will form on the edges and the top of the sauce. If this happens, you can usually reverse it by whisking in a little water or stock to restore an adequate liquid-to-fat balance.