mustard
A condiment of ground mustard seeds mixed with liquid and seasonings, ranging from smooth and mild (yellow) to sharp (Dijon) to coarse and grainy (whole-grain); used as a spread, whisked into dressings, or stirred into sauces for tang and a little heat. It's concentrated -- a spoonful carries salt, acidity, and sharpness all at once, so it's easy to overdo.
Buying guidance
Read the ingredient list, not just the color: yellow, Dijon, and whole-grain mustards differ enormously in heat, salt, and acidity between brands, so what a tablespoon delivers isn't fixed. Whisked into a vinaigrette, mustard also acts as an emulsifier, helping oil and vinegar stay blended rather than separating.
Substitutions
- Dijon for yellow, or the reverse -- Dijon is sharper and less sweet; start with less if swapping in for yellow.
- Whole-grain mustard -- similar flavor with a coarser, poppable texture; fine in a dressing, less smooth stirred into a sauce.
- Prepared horseradish -- shares the sharp bite but no mustard flavor; use sparingly.
Tips & common mistakes
Its sharp bite mellows the longer and hotter it's cooked, so for a bright mustard flavor, stir it in toward the end of cooking rather than at the start of a long simmer.
Storage
Thanks to its natural acidity and mustard oils, prepared mustard keeps well in the fridge for months after opening with little quality loss, longer than most opened condiments -- darkening in color over time isn't a sign it's gone bad.