Reduction as a cooking method predates recorded culinary history — the logic of concentrating flavour through evaporation is universal. The precise, technique-driven approach to sauce reduction was codified in the classical French kitchen from the 17th century onwards.
Reduction is not merely a technique for thickening — it is the primary mechanism by which cooking concentrates, intensifies, and transforms liquid into sauce. When a braising liquid, stock, or wine is reduced, water evaporates and every other compound — sugars, proteins, acids, aromatic molecules — becomes more concentrated. The result is not simply less liquid but a different substance: more intense, more complex, stickier, and more flavourful. The most common application in the restaurant kitchen is taking a braising liquid and reducing it to a sauce. After a long-cooked braise of beef cheeks, short ribs, or oxtail, the cooking liquid is strained, degreased, and returned to high heat. As it reduces, it transforms: at 50% reduction it has developed gloss; at 75% it coats a spoon; at 90% it becomes syrupy and sticky — approaching a glaze. At each stage, the flavour character changes. Finding the right concentration point for a given dish is a matter of judgement that experience alone teaches. Thickening mechanisms in reduction sauces include natural gelatin (from bones in stock), natural sugars, and sometimes starch additions (arrowroot slurry for a clear, glossy finish; cornstarch for a more opaque thickening). Pure reduction without thickeners, relying on collagen-rich stocks, produces the most elegant sauces — they coat naturally and cling rather than gloop. Degreasing is a critical step: fat must be removed before or during reduction, either by skimming the surface, using a fat separator, or refrigerating overnight so the solidified fat can be lifted off cleanly. Fat left in the reduction creates an oily, murky sauce rather than a glossy one. Once reduced and degreased, mounting with cold butter, adding aromatic herbs, or finishing with a splash of acid completes the sauce.
Intensified, complex, and increasingly sticky as water leaves — concentration is transformation
Degrease the liquid before or during reduction — fat clouds the sauce and adds nothing Reduce at a vigorous simmer, not a rolling boil — violent boiling causes emulsification of fat Skim constantly during reduction to remove surface proteins and maintain clarity Know your concentration target — 50% for a jus, 75% for a sauce, 90% for a glaze Finish with cold butter (mount) for gloss, or acid for brightness, always off the heat
Refrigerating the braising liquid overnight and lifting the solidified fat gives the cleanest base For a very glossy reduction, add a sheet of gelatine bloomed in cold water per 500ml of liquid Arrowroot slurry (1 tsp per 250ml) added to a barely simmering reduction gives a clear, glossy thickening without the starchy flavour of cornstarch For wine-based reductions, the wine must be added early and reduced separately to eliminate alcohol before the stock goes in A finished braising reduction can be portioned and frozen — it reheats perfectly and is infinitely more useful than commercial gravy
Not degreasing — produces an oily, murky sauce Boiling too hard — emulsifies fat into the liquid creating a cloudy result Not skimming — protein foam incorporated into the reduction creates bitterness Over-reducing — sauce becomes sticky, sweet, and cloying rather than balanced Seasoning before reducing — salt concentrates; always season at the end