(Mishnah): One who buys from an Am HaAretz baker is obligated to separate Maaser and Challah - how should he tithe? He takes from the bread an amount for Terumas Maaser (1/100th) and for Challah (1/48th) and he says, "1/100th of what there is here should be Maaser on this side and that (9/100th) which is nearest to it should be the rest of the Maaser Rishon; that which I tithed (1/100th) should be Terumas Maaser (for all of it) and the rest (of what I tithed) should be Challah and that which is on its northern or southern side should be Maaser Sheni which is redeemed onto the money.

(Gemara) Question: Does he tithe even from the part that will become Challah? Is Challah obligated in Demai? Didn't the Mishnah teach earlier (Perek 1 Mishnah 3), "The Challah of an Am HaAretz and Meduma are exempt from Demai"?

Answer (R. Acha/ R. Bun bar Chiya citing R. Yosi ben Chanina): Our Mishnah follows the view of Beis Shammai (who obligates Challah in Demai) as the Baraisa taught - R. Shimon ben Yehuda cited from R. Shimon - Challah of Demai - Beis Shammai obligate and Beis Hillel exempt.

Question: Didn't Beis Shammai obligate it only for something that is for consumption, but as for one who buys to plant, to feed his animals, to make flour for tanning hides or for candle oil, don't they agree that he would be exempt?

Answer: It's when the baker kneaded the dough with fruit juice (so that the dough would not contract Tumah. Therefore, he can also be assumed to have tithed.)

Question: Didn't R. Yosi bei R. Chanina say that the law of fruit juice was said by R. Eliezer ben Yehuda, man of Bartusa...but the Mishnah cannot be according to Rabbanan as they say that dough made with fruit juice is not obligated in Challah?

Answer: We cannot understand the Mishnah according to R. Yochanan who explained (in Perek 2 Halachah 4 - Zevachim 93 (d)-(e)) the seeming contradiction between the earlier Mishnah (the baker tithes) and our Mishnah (the buyer tithes), that the Mishnah there refers to a baker producing the dough in a state of Taharah; and our Mishnah refers to in a state of Tumah. (If so, why would our Mishnah require separating Demai even for the Challah, since it is Tameh and inedible. Isn't the Challah therefore only usable to feed his animals, which is exempt from Demai! See earlier Demai 1:3 - Zevachim 81-2(a))

Rather, it is according to the explanation of R. Eliezer (there), that even our Mishnah refers to one who produces it in Taharah. Our Mishnah can follow Beis Shammai, that if the Challah is for consumption, it is obligated in Demai.

Question: If it is produced in Taharah, meaning by a Chaver, why should it be Demai, since he is trusted for Maaseros - didn't a Baraisa teach that whoever is trusted for Taharos is trusted for Maaseros?!

Answer (R. Yanai bei R. Yishmael): That's only true when one is a guest in his house, but when selling to the public, which is the case here, he is not trusted until he accepts it upon himself in public.

Answer to (R. Avin/R. Shammai citing R. Acha): Learn from the next Mishnah (that there is no obligation of Demai on Challah) - 'If a person wishes to separate Terumah and Terumas Maaser at the same time...' - and just as the Mishnah does not require separating Maaser and Terumas Maaser on the Terumah, so too here, there is no obligation to separate Demai on Challah!