Reduction

Reduction (boiling down) is a fundamental culinary technique in which a liquid (stock, wine, sauce, juice) is boiled or slowly simmered so that part of the water evaporates from it. As a result the volume of the liquid decreases, and its flavour, aroma, and density are concentrated and intensified.

The principle is simple but powerful: as the water leaves as steam, all the non-volatile flavour substances — sugars, acids, gelatine, aromatic compounds — remain and concentrate in a smaller volume, making the liquid thicker, richer, and deeper in flavour. It is by reduction, without any thickeners, that sauces are brought to the required, coating consistency and intensity. Classic examples are demi-glace (meat stock reduced for hours), wine sauces, balsamic reduction (a thick sweetish syrup of vinegar), fruit coulis, tomato sauces. It is important to carry out reduction attentively: at the end, when little liquid remains, the flavour concentrates rapidly, so it is easy to over-salt (since salt too concentrates) or to scorch it. Reduction is in essence the art of patience, when time and heat turn a liquid base into a rich, aromatic essence of flavour. It is one of the key techniques for creating deep, refined sauces.