Mustard Seeds (or Rai) with their exotic, hot and spicy flavour is the main spice in Tadka. For Tadka, heat oil to a temperature where the whole spices pop and splutter. This make the spices release the flavour completely. Mustard Seeds are roasted lightly until they start emitting the flavour, then ground to powder. This powder can be used in Salads and chutneys.