The source names raw, unparboiled Arwa Chawal for Rasiya and Kasar and contrasts it with Usna Chawal. Its purity explanation is reproduced as a ceremonial interpretation, not as a food-safety classification.
The Rule of Arwa Chawal
During the preparation of Prasad for Chhath Puja: especially the Rasiya (Kheer) on Kharna and the Kasar laddus: devotees strictly use Arwa Chawal (raw, unparboiled rice).
Why Parboiled Rice is Banned
Parboiled rice (Usna Chawal) undergoes a boiling and steaming process at mills before being husked. Because it has been processed and handled by external entities in bulk, it is considered ceremonially impure (Jootha) for divine offerings. Arwa Chawal, milled directly from the raw paddy, retains its absolute sattvic purity, making it the only acceptable rice for Chhathi Maiya.