The oriental mustard seed is the hottest of the mustard seeds has a flavor similar to wasabi or horseradish powder. The enzyme myrosine is what creates the pungent taste of mustard. This enzyme is activated by water. Thus, when cooked in oil, the taste of the seeds will remain subtle, and add a less pungent flavor to things like curry pastes.
Oriental mustard seeds are often used to flavor vinegars and are a common ingredient in pickling and preserving spices. Use these seeds whenever a little extra heat is desired.