Mustard Seeds are a key ingredient to any South Indian Cuisine. It’s like how much important cumin seeds are to North Indian cuisine. These tiny seeds are added to the hot oil and popped to release their flavor as part of the tempering process. As part of Tempering, we usually add mustard seeds to the hot oil and let it pop first followed by adding split urid dal, hing and curry leaves. Mustard seeds used in South Indian Kitchen are black or brown in color. If you can’t find them in the market then, you can also use the yellowish seeds more commonly found in western grocers.