Rasam powder is now commercially available . It is an important powder not only for making rasam easily but also in other indian recipes such as gojju, puli ogray, and gojju avval.. Here is an easy way to make rasam powder easily .. this is my own recipe ..  hope it works well for you .. The ingredients - 2 measures red chilly peices, 1 measure dhaniya seeds, 1 measure jeera ( cummin seeds ), one measure yellow mustard seeds ( menthem), 2 measures of curry leaves ( karepak / kare pattha ), 1 teaspoon of hing, 1 teaspoon of haldi ( turmeric powder ).. Take all in a kadai ( except the hing and the haldi ) and roast on a low flame till the chillies and curry leaves get crispy .. be sure to uniformly roast all .. then add the hing and the haldi.. wait to cool to room temperature and grind .. Note: Chillies can be very hot or not so hot ..so you need to find out the correct amount of chillies to add by trials on a small batch first and either increase or decrease the proportion according to taste..