How Much to Separate?
The Torah does not specify an amount that must be separated for challah, bikkurim, or terumah. By contrast, it does specify that one-tenth of the crop is given to a Levi as ma’aser. The Sages determined that a professional baker separates one out of forty-eight parts, while a lay baker separates one out of twenty-four parts.
Why does the professional give less challah? The Ateres Zahav states that the Sages were more lenient with a baker because baking is his livelihood, and the Sages wanted him to enjoy more of the fruits of his labor. The Rambam writes that whereas a baker generally deals with large portions of dough, the amount that he separates, even at the smaller one-forty-eighth ratio, generally is large enough to make a suitable gift to the kohen. A housewife kneads smaller quantities, so that a larger percentage, one-twenty-fourth, is required to make her gift suitable.
The Lubavitcher Rebbe advances a more esoteric reason for the difference. He explains that G‑d wants us to perceive His providence in all that we do. A professional baker is heavily reliant upon a good planting season and a good harvest. He carefully monitors these and thereby witnesses G‑d’s providence throughout the process of flour manufacture. A non-professional sees only the final product. He must give a greater percentage, so that he will have a greater awareness of G‑d’s manifestation.
Today, because the mitzvah of challah is Rabbinic in nature, there is no minimum amount that must be taken. In Israel, there is a widely observed custom to take a k’zayis, the size of an olive.
While both men and women have the obligation to separate challah, this is among the mitzvos that were specially entrusted to women. Where both husband and wife are involved in making dough, it is preferable for the wife to separate the challah.
How large must the dough mass be to require the taking of challah? One must take challah if the dough is at minimum the size of an omer, equivalent to a volume of forty-three and one-fifth eggs. (The omer is the standard of measurement for food in the Torah.) There is a disagreement concerning the precise measurement of an omer. There is a consensus that dough made from five pounds of flour meets the minimum size requirement. A consensus exists as well that dough from less than two and one half pounds of flour is too small to require the taking of challah. Therefore, when one kneads from five or more pounds of flour, she recites the blessing. If flour content is less than two and a half pounds, she does not take challah at all. When kneading between two and a half pounds and five pounds, one does take challah, but should consult a competent Orthodox rabbi regarding the recitation of the blessing.
The blessing made for the taking of challah is “who sanctified us with His commandments and commanded us to separate challah.” A common custom is to say “. . . to separate challah from the dough.” This latter version is not recorded in the Shulchan Aruch, and the Taz, one of the principal commentators on the Shulchan Aruch, notes that he does not know the basis for it. Nonetheless, the custom in many circles is to add the words “from the dough.”
Challah is taken only from five grains: wheat, oats, rye, spelt, and barley. Challah is not taken from rice, corn, or other grains with which dough may be made. Also, challah is taken once the flour and water have been mixed; it cannot be taken before the kneading has been done. And it should be taken before the dough is baked; nonetheless, if one neglected to separate challah before baking, she does so after baking. (In Passover matzoh baking, where we must complete the baking process quickly, we take challah only after baking.)
We separate challah from cake doughs as well as from bread doughs; however, if the majority of the liquid content is juice rather than water, we do not make the blessing. If none of the liquid is water, it is preferable to add a little water and separate challah. (For a detailed, practical exposition of the challah laws, see Spice and Spirit: The Complete Kosher Jewish Cookbook.)
The mitzvah of taking challah serves a number of purposes. It connects the mundane act of food preparation to G‑d, by reminding us that He is the true owner of the land. It also establishes a bond between the common folk and the kohanim, the priests, who are ideally the recipients of the challah. The kohanim, by virtue of the fact that they were deeply involved in the service at the Temple, were unable to engage in farming on a regular basis. Challah, terumah, and the other gifts given them afforded the kohanim sustenance as they performed their work.
Today we do not give challah to the kohanim. While we do have kohanim in our midst, we are unable to verify their lineage beyond any doubt. A non-kohen is not permitted to eat challah. Additionally, nowadays both the kohen as well as the Challah are presumed to be impure, making the challah prohibited even for a verified kohen. Therefore, we destroy the challah by burning it to the point that it is inedible. (Walk into a kosher pizza store, and you will often see a crisply burned ball of dough resting on top of the oven. This is the challah.)