Larger units use steam. The manual packs pre-wetted straw in trays and holds a pasteurisation room at 58-62 C for four hours; the whole cycle takes 3-5 days. The folder's tunnel holds 60-65 C for about four hours.
DMR also describes chemical steeping: straw soaked 12-18 hours in water with a fungicide and formalin, which suppresses competitor moulds for 25-40 days after spawning. This lesson gives no doses; both chemicals carry regulatory and residue conditions, so check current label approval and prefer hot water if unsure.