I am not that familiar with the science of fermentation as it applies to chimutz. My understanding is that we have a concern that if the wheat becomes wet, it starts to be chamet after a certain period of time - I gather 18 minutes?
So, my question, here, is at what point do we need to be concerned about the wheat becoming wet? After all, it rains on the wheat. Farmers use irrigation methods. So the wheat is getting wet. I gather that there is no concern of chimutz while the wheat is still attached to the ground, otherwise, we'd never be able to use it on Pesach.
So, at what point do we have to be concerned - immediately after it's cut? At the point that it's cleaned and the kernels are separated from the chaff? At the point that it's ground into flour?