Reduction viscosity development is the increase in thickness that occurs as a liquid is reduced by evaporation. When water leaves a sauce, stock or syrup, the dissolved and suspended solids become more concentrated. Depending on the ingredients, gelatin, sugars, pectin, starch and other components can contribute to the finished viscosity.
As a liquid simmers, water evaporates and the remaining ingredients become more concentrated. A stock rich in gelatin may feel fuller and coat a spoon more readily as it reduces. A sugar syrup becomes thicker as its sugar concentration rises. A sauce containing starch or puréed vegetables may thicken through additional mechanisms as well as simple evaporation.
Reduction increases concentration by removing water. Thickening can also occur through starch gelatinization, gelatin setting, emulsification or the addition of other thickening agents. A sauce may use more than one mechanism to achieve its final texture.
Assess viscosity at the temperature at which the sauce will be served. Gelatin-rich sauces can thicken significantly as they cool, while a hot syrup may appear thinner than it will be at room temperature. Use the spoon-coating or nappe test when appropriate, but consider the next finishing step as well.
Chef’s tip: do not reduce solely to a target volume. Taste the sauce and check its consistency, remembering that salt, acidity and sweetness also concentrate as water evaporates.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
