Drake's library builds IMO3 on rice bran, not rice hulls. Substrate changes how the microbes grow, and Korean practice leans on rice bran for that reason. (Office Hours Ep. 158, 57:08)
Other substrates appear in the library. Ben's Arizona pile uses rice bran, wheat middlings, rolled barley, and chipped mesquite tree bean pods. (Office Hours Ep. 104, 52:39) A Hawai'i trial used wheat mill run, which the paper lists as a stand-in for any carbohydrate source.
The library does not say whether oats alone work, or oats with wood chips. Whatever you pick, handle the pile the same way:
- Dilute IMO2 500 to 1,000 times with water and mix it into the substrate. Hold moisture at 65-70%. (Cho, Theory, p. 54)
- Turn the pile every two days to bring the heat down and mix the microbes. (Unravelling the Mysteries of KNF, p. 59)
- White fungi across the top mean the inoculation worked. (Unravelling the Mysteries of KNF, p. 59)
