Mustard in cooking can refer to either the spice from seeds of a plant, or prepared mustard, a common condiment. It is used for its pungent flavor in either application. Mustard greens, one of the many brassicas (or cruciform vegetables), contain similarly strong flavor.
Dry mustard in its seed form can be classified as either white mustard, brown mustard or black mustard. Seeds crushed into a fine powder are also readily available in many markets. Mustard seed is among the world's most ancient of flavorings, found in the remnants of Egyptian and Indian civilizations from centuries ago.
Prepared mustard can be found in multiple variations around the world, and usually consist of ground seeds combined with vinegar and water, as well as some other ingredients. The most notable prepared mustards today come from traditions in China, France, the United Kingdom, Germany, the United States.
- Chinese hot mustard is often little more than the combination of pulverized brown mustard seeds and cold water. The characteristic sharp, stinging flavor of the mustard comes from a chemical reaction resulting from putting the seed with cold water.
- French and English mustards typically are among the most potent of the more complex prepared mustards. As early as the 1700s in France, mustard seeds were ground (with or without their hulls) and combined into a thick sauce, and produced commercially. Dijon mustard, the best known of the French mustards, uses brown mustard seeds in varying strengths. It has become common especially in the United States in recent years to combine Dijon mustard with honey for sauces and salad dressings. English mustard, also popularized in its dry form, most commonly uses a combination of white and brown mustard seeds, and has potency often compared to horseradish.
- German mustard receives similar preparation techniques, but is often milder due to the addition of sugar. Many varieties of German mustard, as in some French varieties, are so-called stone-ground mustards, with coarsely ground mustard seeds incorporated into the mixture. This as well as varying additional spices in the recipe such as cracked peppercorns can give some German mustards a differently strong flavor than those from other sources. The stone-ground mustards are also similar to Creole mustard found in Louisiana and other parts of the United States.
- Yellow mustard first became common in the mid-1800s, using mostly white mustard seeds and given a heightened yellow color from the addition of turmeric. Yellow mustard is widely used on hamburgers and hot dogs (or frankfurters) especially in the United States, and is a common condiment for other sandwiches and mixed salads (such as potato salad and tuna salad).