Reduction

A reduction is a liquid, such as stock, wine, cream or juice, that has been simmered or boiled until some of its water evaporates. Reducing concentrates flavour, deepens colour and thickens the liquid without adding flour or starch. It's the backbone of pan sauces, demi-glace and glazes.

How it works

Water evaporates; most flavour compounds, sugars, salts, gelatin and proteins don't. As water leaves, everything else gets more concentrated. Reduce 1 litre of stock to 500 ml and its flavour, salt and body roughly double.

Body comes from what's left behind:

• Gelatin in good stock thickens and gives a sticky, glossy finish.
• Sugars in wine, juice and balsamic turn syrupy.
• Milk fat and proteins in cream thicken it as water leaves.

A long-simmered sauce also darkens through Maillard browning and caramelization of sugars.

Common reduction terms

• Reduce by half / by two-thirds: simmer until 50% or 33% of the original volume remains.
• Au sec: French for "almost dry", with just a tablespoon or two of syrupy liquid left. Often used for wine and shallots at the start of a sauce.
• Nappe: thick enough to coat the back of a spoon.
• Glace: stock reduced so far it sets into a firm jelly when cold. Demi-glace is a classic half-way version.

How to reduce faster

• Use a wide pan. More surface area means faster evaporation; a 30 cm (12 in) skillet works much faster than a tall saucepan.
• Keep it at a brisk simmer, around 95–100 °C / 203–212 °F. A violent boil can scorch the sides and make cream or emulsified sauces split.
• Leave the lid off.
• Start with less liquid. Reducing a litre takes much longer than reducing 250 ml.

Common mistakes

• Seasoning too early. Salt doesn't evaporate. Add it at the end.
• Over-reducing wine without stock, which can taste sharp and harsh. Reduce wine, then add stock and reduce again.
• Reducing cloudy or fatty stock hard, which emulsifies fat into a greasy, murky sauce. Skim first.
• Scorched edges. Wipe or scrape the sides of the pan where dark residue forms.

Quick numbers

• 250 ml (1 cup) red wine reduced au sec: about 5–8 minutes in a skillet.
• 500 ml (2 cups) cream reduced by a third: about 10–15 minutes at a gentle simmer.
• 250 ml (1 cup) balsamic reduced to a glaze: about 10–15 minutes over low heat; it thickens more as it cools.