I think that what we wrote on the Insights to that Daf addresses your question. Here's a copy, let me know if this does not suffice. -M. Kornfeld

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1) PEELING BARLEY ON SHABBOS

QUESTION: The Gemara says that it is permitted to peel barley by the cupfuls in order to remove the seeds on Shabbos. Why is this permitted more than rolling ears of wheat in order to remove the kernels, which the Gemara (12b) prohibits doing on Shabbos?

Second, if one may peel the barley on Shabbos, that means that until now it had not yet been brought to the silo, since it is brought to the silo only after it has been peeled from the husks. If so, it has not yet underwent Miru'ach and become Chayav in Ma'aseros. When one peels the seeds of barley on Shabbos into a hand, they should become Chayav in Ma'aseros at that moment, since that is the "Gemar Melachah," the final processing of the barley. Since Ma'aseros cannot be separated on Shabbos, why is one permitted to peel the barley on Shabbos if he will not be able to eat it in any case since he cannot separate Ma'aser from it on Shabbos? The barley should be Muktzah!

Third, why does the Gemara refer to "peeling" barley and "rolling" wheat? What is the difference between peeling and rolling? Both actions remove the outer shell of the item.

ANSWERS:

(a) TOSFOS (DH v'Im) and TOSFOS RABEINU PERETZ explain that there are two different shells around the kernel of wheat. There is a thin shell which lies directly on top of the kernel, and there is a thicker shell which houses the kernel and its peel. When the Gemara (12b) says that one may not roll ears of wheat, it is talking about wheat that is within both coverings, the outer husk and the inner peel, and one wants to roll it in order to remove the outer husk. That is Asur because it is Dishah (mid'Rabanan).

Since the outer covering was separated from the seed before Shabbos, it may have been lying until now in the silo, after Miru'ach, and thus Ma'aser might have already been separated from the barley before Shabbos. Therefore, the barley which the person is peeling on Shabbos has already had Ma'aser separated from it. The seed has only its inner covering, which one is permitted to peel on Shabbos. (Removing the inner covering is not considered Dishah since the inner peel is like the peel of a fruit, the removal of which is does not fit the definition of Dishah. Dishah involves removing the container of the produce (such as the outer husk); removing the peel is not removing the "container.")

When the Mishnah says that one who peels ("Mekalef") barley and places it into his hand is Chayav (in Ma'aser), it is referring to barley that was not yet brought to the silo, although its outer covering was already peeled, and thus it was not yet Chayav in Ma'aser.

This also explains why the Mishnah uses the term "peeling" ("Mekalef") -- it is referring to taking off the inner peel, as opposed to the outer husk.

(b) RASHI (DH v'Ochel) explains that "Mekalef" refers to removing barley from its outer covering, not like Tosfos. Why, then, is Mekalef not considered Dishah, while "Molel" is? It could be that Rashi understands that removing the covering by an act of peeling, rather than by crushing the entire item, is not considered Dishah. That is why "Mekalef" is not Dishah, and why the act is called "Mekalef" in contrast to "Molel."

Regarding the problem of Ma'aser, TOSFOS RABEINU PERETZ suggests that one separated Ma'aser before Shabbos by taking barley that had already had Miru'ach and separating Ma'aser from that barley for the barley which he intends to peel on Shabbos. The separation of Ma'aser takes effect when he peels the barley on Shabbos (as we find in Kidushin 62a).