Mar Zutra challenges R' Yanai (and R' Yochanan)and the second answer of the Gemara is that R' Yanai also differentiates between produce that has "goren" in the field and produce that requires "bayit." Why doesn't the Gemara at some point raise the apparent "stira" between the pasuk in Korach (dagan) and the pasuk in Ki Tavo (bayit)? Why is the Gemara satisfied with raising a question from one Tannaitic source to another? Wht not kick it up a notch?
Norman Meskin, Yerushalayim
I think that before we learned this Sugya we would not have thought there was a contradiction between (1) Devarim 26:13 and between (2) Bamidbar 18:27 because (1) is not actually referring to separating Terumot and Ma'aseros but rather to the Dinim of Bi'ur - removing from one's house the Terumos and Ma'aseros which have already been separated. (This takes place twice in every 7 years - on Chol ha'Mo'ed Pesach of the Shemitah year [we just performed this a few months ago] and on Chol ha'Mo'ed of the 4th year of the Shemitah cycle). In contrast (2) tells us how to separate the Terumos and Ma'aseros and that this is done in the "Goren" before it enters the house.
However, Rav Yanai made a Derashah on (1) to take it out of its simple meaning and to learn from (2) a Din about Terumos u'Ma'aseros. Because of Rav Yanai we now do seem to have a Setirah between (1) and (2).
In the 2nd answer (the "Iba'is Eima") of the Gemara on 88b the Gemara said that Rav Yanai was not discussing species which have a Goren - the latter is only wheat and barley. In contrast Rav Yanai was discussing grapes and olives which do not have a Goren and therefore there is no Setirah to him from the Beraisa.
KOL TUV
D.Bloom