This applies to liquids like soup, stock, and sauce. The term ‘reduce’ refers to reducing the water volume of whatever it is that you’re cooking. All that you’re doing when you reduce a liquid is boiling off the water content; vaporizing the water from the soup, stock, or sauce. As the water is vaporized, the concentration of the nutrients and flavor increases. The technique is especially useful in sauce making.
In the video tutorial below, we show you an example of classic sauce making. Flavor building requires you to add components and reduce, or concentrate them, before you add more components. For a given sauce, one might start by sweating some shallots in olive oil, adding a teaspoon of maple syrup (real maple syrup), deglazing the pan with 1 tablespoon of sherry vinegar, reducing the vinegar to a glaze and then adding 1 cup of Spanish rose and reducing it by half (slowly turning it into half a cup by simmering) and then adding 2 cups of fish stock and reducing the entire mixture by half, straining it into a smaller pot and adding 3 tablespoons of cream, reducing it further by 25%, stirring in 1 tablespoon of butter and a chiffonade of thai basil and tomatoes cancasse and serving it over seared perch!