Challa: From What Stage?
The Misva to take Challa applies to dough. If one separated Challa directly from the flour, before kneading it with water, it would not be considered Challah. If one did not remember to take Challa until after the loaves were baked, it is still permissible to remove Challa from the baked bread.
Amount Taken
Only a "MaShehu," a miniscule amount, of dough has to be taken for Challah. Although the Arizal said that the preferable amount is 1/48th of the total amount, this is not the widespread custom. Since it is hard to measure and the Misva today is only d’Rabanan (Rabbinically ordained), especially in chutz l'aretz (diaspora), we just take a small amount, and that is sufficient.
Discarding the Challa
What does one do with the separated Challa? The traditional method of discarding Challa is burning. The separated dough is wrapped in foil and burnt over the grate of the stovetop until inedible, and then discarded. If burning is not an option, the Poskim say that it can be wrapped in a bag and placed in the garbage or washed down the drain.
In principle, the Challah could be given to an adult Kohen who is Tahor (pure). Immersing in a Mikve would render him sufficiently pure for eating Challah. Alternatively, it could be given to a Kohen under Bar Mitzva, who presumably was never a Ba’al Keri or a Zav. Although not commonly practiced, if given to a Kohen, he would make a special Beracha upon eating the Challa.
If the dough was inadvertently eaten by a Non-Cohen, B’diavad (after the fact), the rest of the dough is permitted.
Challa from Doubt
If a guest suspects that his host may not have taken Challah from the bread being served, he has the option of discreetly separating Challa from his own portion. He would take a little piece from the bread and put it in his pocket, designating it as Challa without a Beracha. On Shabbat, this is not a solution, since it is prohibited to separate Challa on Shabbat. (Kaf Ha’haim, Rav Yaakob Haim Sofer, Baghdad-Israel, 1870-1939, 242:26)
Non-Jews
The Halacha states that the obligation of Challa is incumbent upon the owner of the dough. If dough, owned by a Jew, was kneaded by a Non-Jew, it is obligated in Challa. Conversely, if a Jew kneads the dough of a Non-Jew, there is no obligation to take Challa.
Mixture
The Halacha states that Challa is "Batel" (nullified) one to one. That is, if Challah was separated and then became mixed back into the dough, the mixture is permissible as long as the dough was at least the equivalent amount as the Challah.
Small Batches
One should prepare dough that has the requisite shiur (amount) for taking Challa. Certainly, one should not specifically try to make a small batch in order to avoid the Misva. Hacham David Yosef, in his Halacha Berura, says that even if the extra amount is not needed, it is better to prepare a large batch and freeze the extra bread, in order to merit the misva.
Obligation on Men and Women
The Misva of Challa is incumbent upon men as well as women.
Extra Flour
The Kaf Ha’haim rules that additional flour added to the kneading surface to prevent sticking is also counted as part of the mixture and is obligated in Challa. Therefore, one should only take Challa after the dough is rolled out and ready to be baked.
