Black, brown, and yellow mustard seeds come from the same family, but different varieties of the plant. The brown mustard seed is smaller and hotter than its yellow counterpart, due to its high oil content. The black mustard seed, which is often used interchangeably with brown, is slightly bolder in flavor and larger in size. Common to Asian and African cooking, black mustard seed is used for hot mustards (i.e. Dijon), spicy pickling brines, oil and spice blends, tangy sauces, and more.