Sawdust is soaked first. The folder gives 16 to 18 hours; the 2011 manual says at least two days. Wheat bran soaks for about three hours. Mix all ingredients thoroughly.
Then move fast. DMR says fill the bags at 1.5 to 2 kg immediately after mixing, because fermentation and contamination start otherwise, and the manual keeps the gap between mixing and sterilising under six hours. Use heat resistant polypropylene bags.