[If] a non-Jew gave [ingredients] to a Jew to make a dough for him, [it is] exempt from challah. [If] he gave it to him as a gift, [if] before he had thoroughly mixed [it], it is obligated [in challah]; but [if] after he had thoroughly mixed it, it is exempt.  [If] one makes a dough [together] with a non-Jew, if [the portion] of the Jew does not consist of the minimum measure for challah [liability], it is exempt from challah.

[Regarding] a proselyte who converted and had a dough, [if] it was made before he converted, he is exempt [from having to separate challah]; but [if it was made] after he converted, he is obligated [to separate challah]. And if it is uncertain [when the dough was made], he is obligated [to separate challah]. But one is not liable on its account to [the penalty of] a “fifth.”  R' Akiva says: Everything follows the formation of a crust in the oven.