Pesachim 3:2-3

Pesachim 3:2

If there is an olive-sized volume of dough in the cracks of a kneading trough, it must be removed. If not, it is nullified because of its insignificant size. The same volume applies in matters of ritual impurity (i.e., a volume of dough that must be removed is considered significant enough to protect the vessel from ritual impurity if touched by an unclean vermin). If one is particular to remove a smaller volume of dough, it will protect the vessel (because it’s significant to the owner of the vessel). If he is content to leave the smaller volume of dough where it is, it is subordinate and considered part of the vessel (and if a vermin touches the dough, it’s the same as touching the vessel itself). If dough shows no sign of rising but there is other dough from this batch that did rise, it is prohibited.

Pesachim 3:3

How does one separate challah (the portion for the kohanim) from ritually-impure dough on yom tov of Passover? (It can’t be given to a kohein because it’s unclean, so it may not be baked because it won’t be eaten on yom tov. It can’t be burned because sanctified foods are not burned on yom tov. If left alone, it will rise.) Rabbi Eliezer says that in such a case the woman does not designate the portion of challah until after the dough has been baked. Rabbi Yehuda ben Beseira says that she puts the dough in cold water (to keep it from rising). Rabbi Yehoshua says that this is not chometz that we are warned not to possess over Passover. Accordingly, it may be left until after yom tov and if it rises, it rises.