Making Mustard First, you need cold liquid. What gives mustard its bite is a chemical inside the seeds reacting with cool or cold liquid. You also need to break the seeds to get at the fiery chemical — it’s like cutting an onion. Heat damages this reaction, however, so to make a hot mustard use cold water, and warm water for a more mellow mustard. Mustard sauces lose punch when long-cooked, and should always have a little extra fresh mustard tossed in at the end of cooking. This reaction is volatile, too. Left alone, your mustard will lose its bite in a few days, or in some cases even hours. But adding an acid, most often vinegar, stops and sets the reaction in place — this is precisely what happens with horseradish as well. Adding salt not only improves the flavor, but also helps preserve the mustard, too.You have three choices when it comes to which variety of mustard seed you use: White, brown and black. White mustard undergoes a different, milder reaction than do brown or black mustards, which are far zingier. American yellow mustard is made with white mustard seed and turmeric, brown mustards are in most of your better mustards, and black mustard is used in hot mustards or in Indian cuisine.Finally, let your mustard set in the fridge or in a cool place for at least a day before you serve it. Bitterness is a byproduct of the mustard reaction, but that bitterness fades after a day or so. Pure mustards can be kept at room temperature, but mustards with other ingredients, like the Roman nut mustard I mention above, should be kept in the fridge.Want herbs in there? Go for it. Like honey mustard? Pour some in. Want your mustard even spicier? Add chillies or freshly grated horseradish.The one caveat to making mustard at home is to wait. You cannot eat it the day you make it. Mustard needs to marinate to dissipate its bitterness. Try it: Eat a little dab right after you make it, then a day or two later. The difference is dramatic. Makes about 1 cup. Prep Time: 12 hours 6 tablespoons mustard seeds 1/2 cup mustard powder 3 tablespoons vinegar (cider, white wine or sherry) 1/2 cup white wine or water 2 teaspoons salt OPTIONAL 2 tablespoons honey 2 tablespoons grated fresh horseradish 1/4 cup minced fresh herbs (really any kind) Grind the whole mustard seeds for a few seconds in a spice or coffee grinder, or by hand with a mortar and pestle. You want them mostly whole because you are using mustard powder, too. Pour the semi-ground seeds into a bowl and add the salt and mustard powder. If using, add one of the optional ingredients, too. Pour in the vinegar and wine or water, then stir well. When everything is incorporated, pour into a glass jar and store in the fridge. Wait at least 12 hours before using. Mustard made this way will last several months in the fridge.