Bhuta Shuddhi is the ceremony of removing the spirits and other beings whose presence many interfere with the performance of rituals and pujas. The Bhuta Shuddhi is performed by offering curd, sugar and flower. This offering is known as Bali in some regions. Bhuta Shuddhi is completed by scattering mustard seeds (black til).
Bhutas are generally believed to be spirits of those dead people who died without fulfilling desires.
The popular belief is that scattering of mustard seeds along with mantras will protect the puja area from evil presence. It is said that if evil in the form of bhutas attempts to enter arena, the mustards seeds will enter them like thunder bolts and drive them out.
Bhuta Shuddhi is performed before important rituals like Durga Puja.