Siman 327

The obligation of challah is from the time of kneading. But if one separated from flour, and placed the challah into the oven – it is nothing, and one must separate another when he kneads. And in a place where they give it to a kohen, we learned in the Mishnah of Challah (Mishnah Challah 2:5): One who separates his challah as flour – it is not challah, and it is theft in the hand of the kohen. And it is not only necessary to say if he is an am ha'aretz who did not know the law. Even if he is a talmid chakham and knows the law, and we should have said that he gave him the flour as a gift, nevertheless he is obligated to return it, for if he does not return it, it will lead to a pitfall, as they will say that it is challah (Taz, subsection 1, from Kiddushin 46b, see there). Therefore, even the flour that is with the kohen, if it contains five revi'im – it is obligated in challah, and so too the flour in the hand of the homeowner. Nevertheless, the flour is forbidden to a zar, because the name "challah" was called upon it. Thus the Tur ruled according to the Mishnah there, for Rabbi Yehoshua holds so, see there. However, the Rambam explains there a different explanation, see there.

Specifically when one separated flour, it is not effective if he says that the name "challah" shall take effect upon it immediately. However, if he separated a portion of flour and said, "When it becomes dough, the name 'challah' shall take effect upon this portion of flour," when it also becomes dough, it is challah. And this is not like one who separated something that has not yet come into the world, since it is in his power to knead it immediately, and anything that is in his power is not considered something that has not yet come into the world. And for this reason, one can also appoint a messenger for the separation of challah while it is still flour, such as when a woman says to her friend, "Knead flour for me and separate challah on my behalf." And even though we hold that any matter that he himself cannot do, a messenger also cannot do (Nazir 12b), this is not called "cannot do" since it is in his power to knead now. However, our teachers, the authors of the Tosafot, wrote there in Nazir that for this reason alone it is not sufficient, but rather since it is in his power to take rolled dough and say, "Let this be challah for this dough when it is kneaded," see there; and it is simple that in such a case, the challah must remain in its entirety until after the kneading. And see what I wrote in siman 328, section 6.

When does the primary obligation of challah take effect? When one adds the water and five quarters of flour are mixed with the water, and there do not remain in the kneading bowl five quarters of flour that have not been mixed with the water. However, if one said, "Behold, this is challah for the dough, for the leaven, and for the flour that remains, and when it all becomes one dough, that which is in my hand shall be sanctified as challah" – behold, this is permitted. And similarly, if one says, "on condition that the challah shall also take effect on the flour that will be mixed in later at the time of preparation," as is the way of women who put flour on the shovel and place the bread upon it, and the flour adheres to the bread. And it is good to teach the women to make such a condition, if there is a concern that five quarters of flour will be mixed in later. But now they are not accustomed to this, because they do not take challah until after the completion of the kneading (Shach, subsection 5). And even though there is still the flour on the shovel as I have written, it can be said that in this there would not be the shiur of challah. However, one must be careful not to burn the challah until after the completion of all the preparation, for if one burns it before – it will not take effect on the dough that is formed afterward.

During the time when purity was practiced in the Land of Israel, they would hasten to take challah due to the concern that perhaps the dough would become impure, and the challah would come to a state of impurity. However, in this time, it is better to wait to separate challah until after the completion of the kneading, so that the entire dough becomes a single body. And ab initio, it is a mitzvah to take challah from the dough, but if they baked before the separation of challah – one should take it after the baking. And regarding matzah, it is necessary to do so, since they bake each dough individually, and in each one there is not the required measure, and it is necessary to join them all into one basket – consequently, they take the challah after the baking. And such is the widespread custom.

We learned in a Mishnah at the beginning of the third chapter (Mishnah Challah 3:1): One may eat a snack from the dough until it is rolled in the case of wheat, or formed into a mass in the case of barley. That is to say: just as with terumah, where before the completion of the work it is permitted to eat a snack and afterward it is forbidden; and the completion of the work for terumah is the smoothing of the pile. So too with challah; and the completion of the work for challah is the rolling, for when the dough is properly rolled it is called "completion of the work." And regarding barley, because the flour does not adhere well, it is called "forming into a mass." It is all one and the same, and the main point is that the entire dough becomes a single body. And now in the Diaspora, where one eats and afterward separates — there is no practical difference in this, as is understood.