Challah 4:5-6

Challah 4:5

If there were two doughs, each containing a kav (about 1.25 liters) of flour, and challah was taken from each of them, then later the two doughs were combined (two kav being the volume Biblically obligated in challah), Rabbi Akiva says that what he already took counts as challah but the Sages require one to take challah from the combined dough. According to Rabbi Akiva, the stringent practice of taking challah from doughs smaller than two kavs becomes a leniency in that one need not take it from the new two-kav dough.

Challah 4:6

One may take the volume of challah from dough that has not yet had challah separated and that is being prepared in a state of ritual purity in order to keep taking challah from it for demai (doubtfully tithed grain) until this dough goes bad. This is because challah for demai may be taken from ritually clean dough for ritually unclean dough, and it may be taken from dough that is not near the demai.