Mustard seeds come from various mustard plants. The plants produce beautiful yellow flowers which then turn to pods that contain the seeds. These Yellow mustard seeds are generally larger than brown mustard seeds but not as pungent as black or brown seeds. The one exception is small yellow Chinese or ‘oriental’ mustard seeds, which are extremely spicy. White or yellow mustard seeds are the primary ingredient in American mustards and are also used in pickling spice mixes.