Masechet (tractate) Menachot, Perek Vav (Chapter Six), Mishnah Vav: A minchah (meal offering) that was brought had to be made from very pure, fine flour, with all impurities or anything else mixed in removed. To do that, they had to sift the flour many times until everything was discovered and taken out. Each time they sifted the flour, its quantity decreased. Not only was the bad stuff eliminated, but some acceptable flour was also lost through repeated sifting. Therefore, they had to start production with more grain than was needed for the minchah, accounting for the loss that would occur through sifting. Here, we'll talk about how much produce was used to produce the menachot (meal offerings).
The Mishnah says, “Ha'omer haya ba isaron (one-tenth of an ephah) mi'shalosh se'in (a dry measure).” The Omer: Ha'omer minchah, which consists of an isaron of fine barley flour, was sifted from three se'ah of fresh barley. Three se'ah of fresh barley is a total of ten isaron. Since barley had a tremendous amount of shells and chaff, a lot of barley was needed to produce one isaron. They started with ten isaron, and through repeated sifting until all the impurities were removed, they finally got one isaron.
Shtei haLechem consisted of two loaves, each with its own isaron, for a total of two isaron of wheat flour. That flour was sifted from three se'ah of fresh wheat. Wheat does have chaff and shells, but not as much as barley. Two isaron of fine wheat could be produced from three se'ah, which is ten isaron. We said before that when it came to barley, ten isaron—the three se'ah—created one isaron of barley flour. Here, ten isaron created two isaron of fine wheat flour.
Lastly, Lechem haPanim (showbread): Lechem haPanim, esrim ve'arba'ah esronim, consisted of twenty-four isaron of fine wheat flour. The person here would use me'esrim ve'arba'ah se'ah. He would use twenty-four se'ah of old wheat. That's how he would get the fine wheat flour. Basically, to produce twenty-four esronim, he needed to start with twenty-four se'ah. That's a three-x multiple. There are three esronim in each se'ah, so to create twenty-four esronim, he needed twenty-four se'ah. So that's basically seventy-two: seventy-two esronim of flour here to create the twenty-four.
Just to review: In the first case, you need a ten-time multiple: three se'ah, which is ten isaron of grain, to create one isaron of barley flour. That's a ten-x. In the second case we discussed, the Shtei haLechem, you needed a five-x. The Shtei haLechem were two esronim, and you needed three se'ah to create that. So three se'ah, which is also ten isaron, creates two isaron. So that's a five-time multiple. Lastly, for the esrim ve'arba'ah esronim—the twenty-four isaron of fine wheat flour needed for the Lechem haPanim—you needed twenty-four se'ah, which is seventy-two isaron. So it's a three-x multiple. Old wheat has barely any chaff, much less chaff than fresh wheat. A single isaron of fine flour could be produced from one se'ah of old wheat, which is three times. And eventually, three-x created that one.