Reducing a sauce

Why

When you reduce a sauce, simmering it uncovered, water evaporates while flavour compounds, sugars, gelatin from meat and bones and salt stay in the pan, so they become concentrated and the sauce thickens. If you salt it at the start and then reduce it by half, it will be roughly twice as salty – which is why seasoning is adjusted at the end. The brown bits stuck to the bottom of the pan or roasting tin after searing or roasting (the fond) are among the tastiest parts of a sauce: poured over with stock, wine or water and scraped up, they dissolve into the sauce – this is called deglazing. A gentle simmer is enough; at a hard boil the sauce easily scorches at the edges and on the bottom, and if it contains a lot of sugar or gelatin it reduces into a sticky mass.

How to do it

• Cook uncovered in a wider pan so the water evaporates faster.
• Salt only at the end, once the sauce has the thickness you want.
• Pour hot stock, wine or water over the fond and scrape it off the bottom with a wooden spoon; leave out black, burnt bits, they would make the sauce bitter.
• Keep only a gentle simmer and stir now and then, especially at the bottom and the edges.
• Test the thickness on a spoon: the sauce should coat it thinly; bear in mind it will thicken further as it cools.

If it goes wrong

An oversalted sauce can only be saved by diluting it: add unsalted stock, water or cream and bring the thickness back with a short simmer. Thin a sauce that is too thick or sticky with a little hot water. Pour a scorched sauce into a clean pan at once without scraping the bottom; if it already tastes burnt, it can't be saved.