108:2 If some of the wheat is found to be split or sprouted, the rest may still be used so long as one separates them; otherwise, we must be very careful to make sure that the acceptable wheat outnumbers those that split or sprouted by a ratio of 60:1. Optimally, one should also be careful to separate from the wheat any from which mice had eaten, or ensure that it is outnumbered by good wheat by 60:1. If wheat was brought by boat or stored in a pit, it may be used as long as it is dry and hard and its appearance hasn’t changed. If it was stored in an attic and rain dripped through the roof onto the wheat in several places, it may no longer be used. If a little snow or water fell on it in one place, one may simply remove that part; we assume that the rest is still useable.
108:3 The Jews were already in the practice to be careful about the mill, scraping it thoroughly and cleaning everything than can be cleaned. New containers are used for the flour. (It’s better to get new ones than to put designated Pesach utensils aside from year to year – Mishnah Brurah 453:37.) In a place where there are Torah scholars, they should go to the mill and supervise that everything is being done correctly. In a place where there are no Torah scholars, it is appropriate for every pious person to go personally to supervise the kashering; this is a greater mitzvah than having an agent do it on his behalf. The custom is that the first flour ground after kashering the mill is not eaten on Pesach. If the mill is also used to grind flour that has been soaked, a partition must be set up so that the two don’t mix.