While you may use either dry mustard or whole mustard seeds in all types of pickling, recipes most often recommend whole seeds. Presentation is key for pickled products, and ground spices create a murky brine that can look rather unappetizing. Use dry mustard on the rare occasion it is called for in a pickling recipe, but otherwise stick with the whole seed for the best flavor and quality.
Spices in Pickling
Mustard seeds are used to flavor all types of fresh and fermented pickles. Fresh pickles are those that are preserved using a vinegar-based brine. Fermented pickles use salt as a preservative to help control the fermentation process that turns a vegetable's sugar to acid. The flavor of mustard complements many types of pickles in both commercial and homemade pickles, including those made from cucumbers, radishes, cauliflower, zucchini, tomatoes and cabbage.
Using Mustard Seeds
Add whole mustard seeds to flavor pickling brine or to finished pickles in jars to impart even more flavor. Over time, however, whole pickling spices such as mustard seeds can cause pickles to darken. Place the spices in a muslin bag during the pickling process and remove them before canning to prevent this. Mustard seeds continue to add flavor to pickles throughout their storage, and this may or may not negatively affect the flavor of the final product.
Using Ground Mustard
Ground mustard is best used for pickling projects with a thick or dark pickling brine, which can hide the murky appearance. Use it in recipes for chutneys, relishes and other minced pickles. Some quick-pickled cucumbers also call for cracked mustard seeds, or those that are coarsely ground. Grind mustard seeds yourself using a mortar and pestle until crushed but still quite coarse for the best flavor and to avoid a cloudy appearance in the jar.
For pickling, fresh spices are key to obtaining the best flavor. Regardless of whether you use ground or whole mustard, buy only whole mustard seeds for pickling and crush or grind them yourself as needed. Ground mustard loses its flavor quickly, and poor storage -- near heat or moisture -- can accelerate this deterioration. Always store mustard seeds in a dark, cool location. For ground mustard seeds, use a spice grinder to grind them shortly before making your pickle recipe for the best flavor.