These are the things through which one fulfills the obligation of [eating] matza: wheat, barley, spelt, oats and rye - and the custom is to take wheat initially (Maharil) - but not rice and other types of legumes [kitniyiot], and these also do not come to be leavened and it is [so] permitted to make a cooked food from them. REMA: And some forbid [it] (Tur and Hagahot Maimoniot and Mordechai on the Chapter [entitled] Kol Sha'ah). And the custom in Ashkenaz is to be strict [about this], and one should not change [it]. However, it is obvious that they do not render a cooked food forbidden after the fact if they fall into it. And so [too] is it permitted to light with oils that are made from them and [these oils] do not render a cooked food forbidden if they fall into it. And so [too] is it permissible to store types of legumes in the home (Terumat HaDeshen, Section 113). And the seed of dill (Maharil) and anise and coriander are not types of legumes and it is permissible to eat them on Pesach, and so does it appear [correct] to me.
If one makes dough from both wheat and rice, if it has the taste of [wheat] grain, one can fulfill the obligation with it on Pesach.
If one did not separate [from] the wheat the mice-eaten [portions], it is of no concern. REMA: And similarly if one did not separate from it the grain sprouts. However, it is necessary to ascertain that all of this [the forbidden portions] is not equal to one-sixtieth of the permitted portions. (Hagahot Maimoniot in the name of SMA"K and T"H in siman 114)
It is good to make the mitzvah-matzah from wheat that has been guarded so that no water has fallen on it from the time of harvest, or at least from the time since it was ground [into flour]. But in times of duress, it is permitted to buy flour from the marketplace.
Nowadays, it is forbidden to put [water on] wheat or barley.
[Regarding] sacks which one places flour in throughout the year, if one wants to put flour in them [for Pesach], and launder them thoroughly, it is necessary prior to laundering that all the corner stitching or [the stitching around the patches] if they are patched, be let out.
At the time when on is transporting sacks of flour from the mill, it is forbidden to place them on an animal without a saddle or thick leather under the sack. REMA: And similarly, one should be cautious initially to avoid placing many sacks of flour interpositionally where possible (Mordechai commenting on the end of "Ayloo Overin")
It is customary to pick the millstone because there are occasions when one places moistened grain [in the mill] to make finer flour. It is customary that the first flour ground after the picking should be guarded until after the festival. REMA: And it's common for proactive people to personally go to the site of the millstone to personally see the grinding of the flours (Mordechia)
It is necessary to grind the wheat a day or two prior to kneading it and if it was ground on the eve of Pesach, there are those who say that it is forbidden to knead matza [dough] with it on that day. This is because at the time it is ground, it is steaming hot and will heat the water [applied when kneading] and the dough will be prone to leavening.