Tractate Peah, Chapter 1, Tosefta 6

Notes:

1. Mishna Peah 1:6 says that a person can give Peah as long as the produce exists. This Tosefta comes to clarify what is meant by that.
2. Standing crops means crops that are still attached to the ground. The Torah says that Peah should be left during the harvest. See Vayikra 19:9. The Rabbis learned out from that that the best way to give Peah is while the crops are still attached to the ground. Meaning that the Peah crops should simply be left in the field and not cut. See Talmud Bavli (Bava Kama 94a).
3. The Tosefta’s example applies specifically to grain since bundling sheaves was only done to grain; however the general principal of what the Tosefta is saying is applicable to any type of produce including fruit. After the crops are harvested they are bundled into sheaves and sheaves are left to lay in the field before they are collected into piles. The Tosefta says that a person can simply leave some sheaves in the field for the sake of Peah and fulfill his obligation of Peah that way.
4. After all sheaves are bundled individually they are collected by the farmer and piled into big piles in the field. Then they are carried away to the threshing floor to be threshed. The Tosefta says that the farmer can simply leave some of the sheaves in the pile for the sake of Peah and fulfill his obligation of Peah that way.
5. After the sheaves are brought to the threshing floor they are untied, threshed and winnowed. After the grain has been winnowed it was piled into piles. The threshing floors were usually located in the fields preferably in an open location in order to get the full benefit of the winds. See International Standard Bible Encyclopedia 1913 (entry Agriculture). Therefore the poor people could simply go into the fields to the threshing floors and take the grain left their as Peah. Most probably they would not need to enter any kind of a closed silo where the grain was stored.
6. Once the grain has been piled the piles were evened out and often sealed. The process of sealing consisted of pressing a large wooden seal against the pile. When the instrument was removed it left an impression which would be destroyed should any of the grain be taken away. This allowed the government to keep track of taxes and enabled the owner to detect any theft of grain. Until the grain was put into bags and transported into silos someone slept in the field to guard the piles of grain. See International Standard Bible Encyclopedia 1913 (entry Agriculture).
7. Once the produce was piled into piles and the piles have been smoothed out it was considered to be a finished product and now was obligated in Terumah (heave-offering) and Maaserot (tithes). Therefore if the person still did not give Peah he was obligated to remove Terumah and tithes from the produce and only then leave some for Peah. Peah, as well as other gifts to the poor and ownerless produce, are exempt from Terumah and Maaserot due to a special derivation from a verse in the Torah (Devarim 14:29). See the statement of Rav Yochanan in Talmud Yerushalmi (Terumot 1:3, Daf 6a). However if the Peah has not been given on time and the produce became obligated in Terumah and Maaserot after smoothing of the pile, then even the portion that later would be given as Peah had to have Terumah and Maaserot separated from it. Therefore once the pile has been smoothed out the tithes had to be separated first and only then Peah could be given. For an explanation of what Terumah and Maaserot are see my commentary on Tosefta Berachot 1:1, note 4.
8. The Tosefta does not say if the person can still give Peah after the produce has been moved into a silo. I would guess that the reason the Tosefta did not mention it is because it was a really uncommon case since the poor people could not walk inside the silo since it was a closed building. I suppose that the owner could still take produce outside of the silo, bring it back to the field, and leave it there in order to fulfill his obligation of Peah.