Techniques
Homemade Sauces: Three Techniques That Cover 90% of Situations
Reduction, emulsion, starch thickening: once you understand these three mechanisms, you stop following recipes blindly and you can fix a sauce that goes wrong.
Sauce is what separates a decent dish from one you remember. And yet most people make it either by guesswork or by following a recipe without knowing why. If you understand the three basic mechanisms, you can improvise any sauce and fix whatever goes sideways.
Reduction: concentrate to gain flavor
Reduction means evaporating water from a liquid to concentrate its flavors and thicken it. It's what turns a watery veal stock into a glossy sauce that coats a spoon. The juices a piece of meat gives up, the white wine added to the pan after cooking, pan drippings stretched with broth: all of it can be reduced.
The practical rule: for a sauce that coats, reduce until the liquid barely covers the bottom of the pan, or until a metal spoon stays coated when you lift it out. Medium-high heat, no lid. Watch out for salty sauces: reduction concentrates the salt too. Never salt before reducing.
Emulsion: marrying water and fat
Water and fat don't mix on their own. An emulsion forces the marriage with an emulsifier (the lecithin in egg yolk in mayonnaise, the mustard in a vinaigrette) or by working mechanically at a precise temperature (beurre blanc, hollandaise). Homemade vinaigrette is the simplest example: 1 teaspoon Dijon mustard + 1 tablespoon vinegar + 3 tablespoons oil + salt. The mustard stabilizes the emulsion and you get a smooth sauce, not a puddle of oil with vinegar at the bottom.
For beurre blanc, the classic French sauce, the emulsion relies on the natural lecithin in butter. You reduce white wine and vinegar with a shallot, then whisk in cold butter in small pieces over very low heat, whisking constantly. The temperature must not go above 140°F (60°C), or the emulsion breaks and you get melted butter with a puddle of acidic liquid. If that happens: pour a tablespoon of cold water into the pan and whisk again off the heat. In 7 cases out of 10, it can be rescued.
Thickening: thicken without long cooking
When a sauce is too thin but you don't want to reduce it (because it's already well seasoned, or you're short on time), thickening is the answer. Two simple options.
Cornstarch: mix 1 teaspoon of cornstarch into 2 tablespoons of cold water. Never pour it straight into hot liquid, it lumps. Pour this mixture into the boiling sauce while whisking and cook for 1 minute. The sauce thickens immediately. One teaspoon of cornstarch noticeably thickens about 1 cup (250 ml) of liquid.
Beurre manié: mix softened butter and flour in equal parts (about 1/2 oz or 15 g of each for 1 cup, or 250 ml, of sauce) and whisk it into the simmering sauce in small knobs. The flour blends in gradually. Cook for 2 minutes after adding it to get rid of the raw flour taste.
Diagnosing a failed sauce
Sauce too salty after reducing: you can't take the salt out, but you can dilute with a little cream, unsalted broth or water. Sauce too acidic: a pinch of sugar or a knob of butter stirred in off the heat softens the perceived acidity. Sauce that's grainy or has split (the fat has separated): it heated too fast or too hard. Take it off the heat, add a little cold water, and whisk or blend if needed. Sauce that's dull and flat even though the seasoning is right: often a lack of acidity. A squeeze of lemon juice at the end of cooking almost always wakes up a flat sauce.
