Reduction theory is the principle that simmering or boiling a liquid allows water to evaporate, concentrating the substances that remain. In cooking, reduction increases the concentration of many non-volatile flavour compounds, dissolved salts, sugars, acids and gelatin. It can intensify flavour and body, but it can also concentrate bitterness, excessive salt or other unwanted notes.
As steam leaves a liquid, its volume decreases. Ingredients that do not evaporate with the water become more concentrated. Gelatin and other dissolved solids can increase viscosity, while aromas may become more pronounced—or some delicate volatile aromas may be lost through evaporation. The final result depends on the ingredients, heat, surface area and duration of cooking.
Salt does not evaporate with water. A liquid that is correctly seasoned before reduction may become too salty after its volume decreases. The same concentration effect applies to acids and sugars. Season lightly during early stages and make the final adjustment when the sauce reaches its intended consistency.
Reduction thickens by removing water and concentrating dissolved ingredients. Thickening can also be achieved by adding starch, gelatin, puréed ingredients or other thickening agents. These methods produce different textures and flavour profiles.
Chef’s tip: reduce at a controlled simmer and taste as the liquid concentrates. Use a wide pan when faster evaporation is desired, but avoid scorching and remember that a reduction will often thicken further as it cools.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
