Does mixing dry mustard with water and allowing it to rest improve its flavor?
Brands of dry mustard powder, including McCormick and Colman’s, recommend mixing the powder with water and allowing it to sit for 10 minutes to develop the fullest sharp, tangy flavor. To test this recommendation, we stirred together mustard and water, sampling the mix immediately and at the 10-minute mark. Tasters compared the just-mixed mustard to “cardboard” and “rancid walnuts.” But after sitting 10 minutes, it developed heat and well-balanced mustard flavor. Here’s why: When mustard seeds are ground into powder, their cells are broken down and the enzymes that contribute to flavor are deactivated, but introducing moisture revives the enzymes and allows them to release pungent aromatic compounds.
We then wondered if we could improve our Classic Macaroni and Cheese (which calls for 1½ teaspoons of mustard powder) by first “blooming” the flavor of the powder in cold water for 10 minutes. The answer was a flat no—in a blind side-by-side tasting, tasters didn’t notice any difference between the two batches.
The takeaway: If you’re turning your mustard powder into a condiment where it will stand alone (e.g. spread over a sandwich or dabbed on rich meat like ham), mix it with water and wait for the flavor to bloom. But when mustard powder is combined with other ingredients, such as in a rub or in a barbecue sauce, it's not necessary.