Reducing

What it concentrates

Water leaves; nothing else does. So a sauce reduced by half has twice the concentration of everything dissolved in it: the savoury compounds you wanted, and also the salt, the acid and any bitterness.

This is why the rule is to season at the end, not the beginning. A stock that tastes correctly seasoned before reduction is inedible after it. It is also why a slightly sharp wine sauce becomes an aggressively sour one if you keep going, and why a reduction that has caught even slightly on the base will taste of nothing but burnt.

Doing it well

• Use the widest pan you have. Evaporation happens at the surface, so a wide, shallow pan reduces several times faster than a tall narrow one.
• Keep it at a lively simmer or a gentle boil, not a violent one. Violence scorches the base and, for anything with dairy or fond in it, splits it.
• Do not cover it. A lid returns the water you are trying to remove.
• Stir occasionally and scrape the base, especially once it thickens, because the last third is when things catch.
• Taste as you go, and stop before it is where you want it — a sauce continues to thicken as it cools.
• Reduce before adding dairy where possible. Cream reduces well; milk, yoghurt and soured cream do not.

How far to take it

The classical French names are useful because they describe a texture rather than a volume.

Reduced by a quarter

Slightly concentrated. Enough for a soup or a braising liquid.

Reduced by half

The everyday target for a pan sauce or a wine reduction.

Nappé

Coats the back of a spoon and holds a line when you draw a finger through it. The standard for a sauce.

Glace

Reduced to a syrupy, intensely savoury glaze that sets solid when cold. A stock reduced by ninety per cent or more.

Too far

Salty, bitter, sticky, and impossible to correct except by adding unsalted liquid and starting again.

When reducing is the wrong answer

• When the sauce is already correctly seasoned. Thicken it with starch instead, or with butter.
• When it contains dairy that will split — yoghurt, soured cream, milk.
• When time is short. Reduction is slow. A cornflour slurry takes thirty seconds.
• When the liquid is already bitter or over-salted. You will make both worse.
• When there is delicate food sitting in it. Take the food out, reduce the liquid, put it back.

What reduction does besides thicken

• Concentrates flavour. Everything dissolved in the liquid stays behind as the water leaves, so the sauce gets deeper as well as thicker.
• Concentrates salt. Which is why a sauce destined to be reduced should be seasoned at the end, not the beginning. This is the commonest way a good reduction is ruined.
• Cooks off alcohol and harshness. Wine reduced properly tastes round; wine added and served immediately tastes raw and sharp.
• Builds body from gelatine. A stock with gelatine in it goes glossy and coats a spoon as it reduces. A stock cube dissolved in water never will, however far you take it.
• Improves colour and gloss. A reduced sauce shines in a way a starch-thickened one does not.
• Cannot be undone. Over-reduced is fixable by adding liquid, but the concentrated salt stays. Taste as you go.

Common questions