To prevent lumps when thickening a soup or sauce, hot liquid should always be added to which of the following?

When thickening a soup or sauce, using a cold roux is the most effective choice for preventing lumps. A cold roux is a mixture of flour and fat that has been cooked together and then cooled. When hot liquid is gradually added to the cold roux, it allows the flour particles to hydrate slowly and incorporate smoothly into the liquid, minimizing the risk of lumps forming.

The process ensures that you control the integration of the thickening agent into the hot liquid. If you were to add hot liquid to a cold roux, the sudden temperature change would allow the starches in the flour to gelatinize more evenly, promoting even thickening without clumping. This technique enhances the texture of the finished dish.

In contrast, adding hot liquid to a thick roux, hot slurry, or hot roux may not give you the same even result. When hot ingredients are combined directly with these mixtures, it can result in lumps as the starches may gelatinize too quickly or unevenly. Thus, using a cold roux in this scenario helps achieve a smoother and creamier soup or sauce.