Water boiled with Black sesame makes body pure. Black til is mixed in either milk/ water and then offered to Lord Shiva in the form of Abhishek. It is equivalent to doing abhishek with 'panchamrat' (a combination of 5 things). This seed is very dear to the Pitars (deceased ancestors). Shastras say that it make the person cross the Vaitarini - the sea of bad karma. One has to cross the Vaitarini to reach Vaikunta loka. During the shraadh ceremony the Kartha makes a special offering of black sesame seeds to pitars.