Maseches Menachos, Chapter 6: This mishnah closes the chapter, and we continue to discuss the preparation of the fine flour for making the minchah. The subject of our mishnah is the sifting. As in the previous mishnah, two principles underlie the matter:
Barley flour is coarser, and therefore requires more sifting than wheat flour.
Flour from new grain requires more sifting than flour from old grain.
The number of sifters for each minchah:
"Omer hayah menupeh bishlosh esreh nafah" - the omer was sifted through thirteen sifters. Thirteen separate sifters were used, one above the other: the top one had the largest openings, and from there on the openings grew progressively smaller, until the finest possible flour was obtained.
"Ushtei halechem bishteim esreh" - the two loaves required twelve. The two loaves come from wheat and not from barley, and therefore twelve sifters suffice for them.
"Velechem hapanim be'achat esreh" - and the showbread required eleven. The showbread comes from wheat, and also from old grain, and therefore eleven sifters suffice for it.
The Gemara describes that in the lowest of the thirteen sifters, the holes are so small that nothing passes through them but dust alone. It emerges that the ideal flour for use is precisely what remains in the lowest sifter, since that is the soles, the fine flour; whereas what falls through those holes is not fine flour at all, but merely dust.
The opinion of Rabbi Shimon:
"Rabbi Shimon omer: lo hayah lah kitzbah" - Rabbi Shimon says: there was no fixed measure for it. Rabbi Shimon disagrees on two points. First, regarding the quantities of raw grain taught in the previous mishnah: there is no fixed measure, meaning there is no set amount with which one begins; rather, one takes the amount of flour that is needed, however much that may require.
Second, "Ela soles menupah kol tzorkah hu meivi" - rather, he brings fine flour sifted as much as it needs. Here too, with regard to the sifting, there is no fixed number; rather, one sifts as much as necessary, until the flour reaches the level of quality called soles. Whether one sifting is required or a hundred, one must do what is needed.
"Shene'emar: velakachta soles ve'afisa" - as it says: and you shall take fine flour and bake it. From here we learn that one must make sure the flour is sifted as much as it needs until it qualifies as soles, however long that takes.
This is how Rabbi Shimon's words are read according to most opinions, as two separate points of dispute. But some read the second part differently: the verse "velakachta soles ve'afisa" comes to teach that the obligation resting on a person is simply to acquire soles. The manner of its preparation makes no difference; what matters is the result - to obtain soles, and that is all.
In summary: The halachah does not follow Rabbi Shimon, but rather the first tanna: one must sift through thirteen sifters for the omer, twelve for the two loaves and eleven for the showbread, and one must begin with the quantity of grain taught in the previous mishnah. But after the fact, as long as he has the correct quantity and the flour qualifies as soles, the minchah is valid.