הלכות ביכורים ושאר מתנות כהונה שבגבולין פרק ז׳ Rambam · Hilchos Bikkurim 7

שְׁתֵּי עִסּוֹת שֶׁיֵּשׁ בִּשְׁתֵּיהֶן שִׁעוּר הַחַיָּב בְּחַלָּה וְאֵין בְּאַחַת מֵהֶן כַּשִּׁעוּר וְנָגְעוּ זוֹ בְּזוֹ וְנָשְׁכוּ זוֹ אֶת זוֹ אִם הָיוּ שֶׁל שְׁנַיִם אֲפִלּוּ הֵן מִמִּין אֶחָד פְּטוּרִין מִן הַחַלָּה. שֶׁסְּתָם שְׁנַיִם מַקְפִּידִין. וְאִם יָדוּעַ שֶׁאֵינָן מַקְפִּידִין עַל עֵרוּב הָעִסּוֹת הֲרֵי אֵלּוּ מִצְטָרְפוֹת:

[The following laws apply when] there are two doughs that when combined comprise the measure that obligates the separation of challah, but neither comprises that measure alone should they touch each other and become attached to each other.The Radbaz emphasizes that touching each other is not sufficient; the two doughs must become attached. See Shulchan Aruch (Yoreh De'ah 325:1). If they belong to two individuals,Who are not partners (Siftei Cohen 326:1). they are exempt from challah even though they are of the same type of grain.See the following halachah which distinguishes between doughs made from one type and those made from two. See also Chapter 6, Halachot 16-17, which deal with the issues mentioned in this and the following halachot. [The rationale is that] we assume that the two people object [to the combination of their doughs].Thus even if they were kneaded together, since they were intended to be separated, they are considered as distinct entities. If it is known that they would not object to the combination of their doughs, they are considered as one.

הָיוּ שְׁתֵּיהֶן שֶׁל אִישׁ אֶחָד אִם הָיוּ מִמִּין אֶחָד מִצְטָרְפִין וְחַיָּבוֹת בְּחַלָּה וְאִם מִשְּׁנֵי מִינִין הָיוּ אֵין מִצְטָרְפִין. שֶׁסְּתָם אֶחָד אֵינוֹ מַקְפִּיד. וְאִם הָיָה מַקְפִּיד שֶׁלֹּא תִּגַּע עִסָּה זוֹ בְּזוֹ וְלֹא תִּתְעָרֵב עִמָּהּ אֲפִלּוּ הָיוּ מִמִּין אֶחָד אֵין מִצְטָרְפוֹת:

[Different rules apply if] the two belonged to one person. If they were from one type [of grain], they are combined and challah is obligated to be separated from them. If they are from two types, they are not combined. [The rationale is that] we assume that one person does not object [to the combination of his doughs].Since they both belong to him and are of the same type of grain, why would he object to their combination?
This, however, applies only when the two doughs are types that would normally be mixed together. If they would not be normally mixed, even if they are owned by one person, this principle does not apply [Shulchan Aruch and Rama (Yoreh De'ah 326:1)]. If he objects [to their combination and endeavors] that one dough not touch the other or become mixed with it, they are not considered as one, even if they are of one type of grain.

וְכֵיצַד מִצְטָרְפוֹת. אִם הָיוּ שֶׁל אֶחָד מִמִּין אֶחָד עִסַּת הַחִטִּים שֶׁנָּגְעָה בְּעִסַּת הַכֻּסְּמִין מִצְטָרְפוֹת. נָגְעָה בִּשְׁאָר הַמִּינִין אֵין מִצְטָרְפוֹת. וְכֵן עִסַּת שְׂעוֹרִין שֶׁנָּגְעָה בְּעִסַּת הַכֻּסְּמִין אוֹ שִׁבּלֶת שׁוּעָל אוֹ שִׁיפוֹן וְכֵן עִסַּת כֻּסְמִין וְשֶׁל שִׁבּלֶת שׁוּעָל וְשֶׁל שִׁיפוֹן שֶׁנָּגְעָה כָּל אַחַת מִשְּׁלָשְׁתָּן בַּחֲבֶרְתָּהּ הֲרֵי אֵלּוּ מִצְטָרְפוֹת:

What is meant by the statement that if they belonged to one person and were from the same type [of grain] they are combined? When a dough from wheat touchesAnd becomes attached. This applies to all the other instances when touching doughs are mentioned in this chapter. a dough from spelt, they are combined.Although they are from different species, since they are of the same general type (for the doughs made from the two are similar, see Chapter 8, Halachah 4), they are combined. If it touched [a dough from] another type of grain,I.e., barley, oats, or rye. they are not combined.Despite the fact that if the different species of grain are mixed in the same dough, they are combined, as stated in the following halachah. Similarly, if a dough of barley touches a dough of spelt,Although spelt is often associated with wheat (ibid.), its dough can be combined with that of rye. oats, or rye, or doughs of spelt, oats, or rye touch each other, they can be combined.The Shulchan Aruch (Yoreh De'ah 324:2) mentions the Rambam's perspective as a minority ruling, favoring the opinion of Rabbenu Asher who maintains that rye can be combined with barley and with spelt, but not with oats or wheat. And oats can be combined with barley and spelt, but not with rye or wheat.

עִסַּת חָדָשׁ אֵינָהּ מִצְטָרֶפֶת לְשֶׁל יָשָׁן אַף עַל פִּי שֶׁהֵן מִמִּין אֶחָד. כְּדֵי שֶׁלֹּא יֹאמְרוּ תּוֹרְמִין מִן הֶחָדָשׁ עַל הַיָּשָׁן. וְלֹא יִתְרֹם מֵאֶמְצַע שְׁתֵּיהֶן אֶלָּא יָבִיא עִסָּה אַחֶרֶת חָדָשׁ אוֹ יָשָׁן וְיִצְטָרֵף לָהֶם לְהַשְׁלִים הַשִּׁעוּר. בַּמֶּה דְּבָרִים אֵמוּרִים בְּעִסָּה שֶׁנָּגְעָה בְּעִסָּה אַחֶרֶת. אֲבָל הַבּוֹלֵל קֶמַח חֲמֵשֶׁת הַמִּינִין וְעוֹשֶׂה מֵהֶם עִסָּה אַחַת הֲרֵי חֲמִשְּׁתָּן מִצְטָרְפִין לְשִׁעוּר עִסַּת חַלָּה כְּמוֹ שֶׁבֵּאַרְנוּ:

A dough from grain from one year should not be combined with a dough from grain from the previous year even though they are of the same species. [This is a decree,] lest people say that terumah may be separated from new grain for old grain.See Hilchot Terumah 10:18. A person should not separate [the challah] from the middle of the two.I.e., taking a portion of both of the two doughs. This advice was given by Rabbi Yishmael (Challah 4:4). Instead, he should bring another dough - either from this year or the previous - and combine it with them to complete the required measure.I.e., placing the doughs of new grain on either side of the dough of old grain or the doughs of old grain on either side of the dough from new grain. Since the person will see that he is adding an extra dough, he will not err and think that one may separate terumah from new grain for old grain [Kessef Mishneh; Shulchan Aruch (Yoreh De'ah 324:8); see Halachah 6]. The Radbaz offers a different explanation.
When does the above apply? When one dough touches another. If, however, one mixes flour from the species of grain and makes a single dough from one of them, the five are combined to comprise the measure of dough required for challah, as we explained.Chapter 6, Halachah 15.

עִסָּה שֶׁהִיא פְּחוּתָה מִכַּשִּׁעוּר מִכָּאן. וְעִסָּה פְּחוּתָה מִכַּשִּׁעוּר מִכָּאן. וְעִסָּה שֶׁאֵינָהּ חַיֶּבֶת בְּחַלָּה בְּאֶמְצַע כְּגוֹן עִסַּת אֹרֶז אוֹ עִסַּת תְּרוּמָה אוֹ מְדֻמָּע אוֹ עִסַּת עַכּוּ"ם. אַף עַל פִּי שֶׁנּוֹגְעוֹת זוֹ בָּזוֹ אֵינָן מִצְטָרְפוֹת שֶׁהֲרֵי דָּבָר הַפָּטוּר מִן הַחַלָּה מַבְדִּיל בָּאֶמְצַע:

When there is a dough that is less than the required measure on one side and another dough less than the required measure on the other side,The two doughs on the sides are of the same type of grain and together, they comprise the required measure. and a dough that is exempt from challah in the middle - e.g., a dough of rice, a dough of terumah [flour] or from terumah [flour] that was mixed with ordinary flour, or a dough from a gentileSee Chapter 6, Halachot 2-4, 9-10, which mention the exemption of these doughs. - [the doughs] are not combined even though they touch each other.I.e., the two external doughs touch the middle dough. If, however, the two external doughs are touching, challah must be separated from them. [The rationale is that] an entity that is exempt from challah separates in the middle.

הָיָה בָּאֶמְצַע עִסָּה שֶׁהוּרְמָה חַלָּתָהּ מִצְטָרְפוֹת שֶׁהָעִסָּה שֶׁבֵּינֵיהֶן כְּבָר הָיְתָה מְחֻיֶּבֶת בְּחַלָּה. וְכֵן אִם הָיָה בֵּינֵיהֶן עִסַּת הֶקְדֵּשׁ מִצְטָרְפוֹת מִפְּנֵי שֶׁרָאוּי לִפְדּוֹתָהּ וְתִתְחַיֵּב בְּחַלָּה. וְכֵן אִם הָיְתָה בֵּינֵיהֶן עִסַּת מִין אַחֵר אוֹ עִסַּת אִישׁ אַחֵר אוֹ עִסַּת חָדָשׁ הֲרֵי שְׁתֵּי הָעִסּוֹת שֶׁבַּצְּדָדִין מִצְטָרְפוֹת לְחַלָּה:

When, by contrast, there is a dough from which challah was separated between them, [the two outer doughs] can be combined, because originally, there was an obligation to separate challah from the dough in the center.In all the instances mentioned in this halachah, the governing principle is that even if the dough in the center cannot be combined with those on the side (as explained in Halachot 1-4), since it is fit to require the separation of challah, it does not prevent the doughs on the side from being combined. Similarly, if a dough that was consecrated was in the center, they are combined, [because that dough] is fit to be redeemedThis is speaking about a dough that was not consecrated until after it was made. If it was consecrated before it was rolled together, it is not fit to be redeemed. See Chapter 8, Halachot 6-7. [at which point,] there will be an obligation to separate challah from it. Similarly, if there was a dough of another type of grain, a dough belonging to another person, or a dough from a different year between them, the doughs on the sides are combined [to comprise an obligation to separate] challah.

שְׁתֵּי עִסּוֹת שֶׁכָּל אַחַת מֵהֶן פְּחוּתָה מִכַּשִּׁעוּר שֶׁהִפְרִישׁ חַלָּה מִזּוֹ וְחַלָּה מִזּוֹ וְחָזְרוּ וְנָגְעוּ זוֹ בָּזוֹ וַהֲרֵי בִּשְׁתֵּיהֶם כַּשִּׁעוּר חַיָּבִין לְהַפְרִישׁ מֵהֶן חַלָּה שֶׁהַחַלּוֹת הָרִאשׁוֹנוֹת אֵינָן כְּלוּם:

There were two doughs, each one of them less than the minimum measure for challah. One separated challah from each of them. Afterwards, they touched each other and [the combined doughs] comprise the [required] measure. There is an obligation to separate challah [from the combined doughs], for the challot separated originally are of no consequence.As stated in Chapter 6, Halachah 16.

שְׁנֵי עַכּוּ"ם שֶׁעָשׂוּ עִסָּה כַּשִּׁעוּר וְחִלְּקוּהָ וְאַחַר כָּךְ נִתְגַּיְּרוּ. וְהוֹסִיף כָּל אֶחָד עַל חֶלְקוֹ אַחַר שֶׁנִּתְגַּיֵּר עַד שֶׁהִשְׁלִימוּ לַשִּׁעוּר הֲרֵי זוֹ חַיֶּבֶת. שֶׁלֹּא הָיְתָה לָהּ שְׁעַת חוֹבָה כְּשֶׁהָיוּ עַכּוּ"ם שֶׁהֲרֵי פָּחוֹת מִכַּשִּׁעוּר הָיָה בְּיַד כָּל אֶחָד מֵהֶן:

Two gentilesIn contrast to two Jews or a Jew and a gentile, as explained in the following halachot. made a dough comprising the required measure [for challah]Since they were gentiles (see Chapter 6, Halachah 8) at the time the obligation to separate challah could have taken effect, the mitzvah of challah is not relevant to them at all . Hence, the exemption because the dough was made with the intent that it be divided into small portions (see ibid. 19) is not significant. and divided it. Afterwards, they convertedIf, however, they divided the dough after they converted, there is no obligation to separate challah even if they added to the dough. For in such an instance, they would be comparable to the two Jews mentioned in the following halachah (Rambam LeAm). and after the conversion, each one added to his portion until it comprised the [required] measure. There is an obligation [to separate] challah. [The rationale is that] there was no time that it was of the size obligating [challah] while they were gentiles, because each was to receive less than the required measure.Hence we do not say - as is said with regard to the following halachah - since the dough was exempt at the time when it could have been obligated, it cannot become obligated again.

אֲבָל שְׁנֵי יִשְׂרְאֵלִים שֶׁעָשׂוּ כָּךְ וְחָזַר כָּל אֶחָד אַחַר שֶׁחִלְּקוּ וְהוֹסִיף עַל חֶלְקוֹ עַד שֶׁהִשְׁלִימוֹ לַשִּׁעוּר הֲרֵי זוֹ פְּטוּרָה. שֶׁכְּבָר הָיְתָה לָהּ שְׁעַת חוֹבָה וְהֵן הָיוּ פְּטוּרִין בְּאוֹתָהּ שָׁעָה מִפְּנֵי שֶׁעֲשָׂאוּהָ לְחַלֵּק:

If, however, two Jews made [a dough] in the above manner and then, they divided it and each one of them added to his portionThe Siftei Cohen 326:8 emphasizes that for this law to apply the addition must be less than the size that obligates the separation of challah. until it comprised the required measure, it is exempt. [The rationale is that] there was a time when there would have been an obligation [to separate challah from the original dough]Had it belonged to one person. and they were exempt at that time, because the dough was made to be divided.And since the obligation was not incurred at the time it could have been incurred originally, it cannot be incurred afterwards.
The Ra'avad objects to this ruling. He admits that it appears to have a source in the Jerusalem Talmud (Challah 3:4), but argues that logically, it is hard to distinguish this from a situation where a person made a dough smaller than the required size and then attached it to a dough of the required size (see Chapter 6, Halachah 16). Hence, he rules that both Jews should separate challah from the dough after they increased its size.
The Radbaz and the Kessef Mishneh support the Rambam's ruling, differentiating between the two instances by explaining that when a dough is smaller than the required size, it has never reached a state where the obligation to separate challah relates to it. In contrast, in the instance described here, the dough was of the size that obligates the separation of challah and it was exempted. The Shulchan Aruch (Yoreh De'ah 326:4) quotes the Rambam's view.

הָיְתָה הָעִסָּה בְּיַד הָעַכּוּ"ם וְהַיִּשְׂרָאֵל בְּשֻׁתָּפוּת וְחִלְּקוּ. וְאַחַר כָּךְ נִתְגַּיֵּר הָעַכּוּ"ם וְהוֹסִיף הַגֵּר עַל שֶׁלּוֹ [וְיִשְׂרָאֵל עַל שֶׁלּוֹ] עַד שֶׁהִשְׁלִים כָּל אֶחָד עִסָּתוֹ לַשִּׁעוּר שֶׁל יִשְׂרָאֵל חַיֶּבֶת וְשֶׁל עַכּוּ"ם פְּטוּרָה:

[Different rules apply when], by contrast, the dough was owned by a gentile and a Jew in partnership and they divided it.The Radbaz and the Kessef Mishneh explain that this is speaking about a situation where the two had not originally intended to divide their dough and then decided to divide it. Had they originally intended to divide it, it would be necessary to separate challah from the portion belonging to the convert as well. If, afterwards, the gentile converted and then added to his portion and the Jew added to his portion until each one of them completed the measure that requires the separation of challah, there is an obligation to separate challah from the dough of the Jew,In contrast to the situation mentioned in the previous halachah, the dough was not originally intended to be divided. Hence, since the gentile has a portion in it, while it is whole, it is not considered as if the mitzvah of challah relates to it. Thus the Jew's portion of the dough was never of the size that requires the separation of challah and when he increases its size, an obligation is created (Radbaz). but the dough of the gentileI.e., the convert. is exempt.Since originally, the gentile's involvement in the dough caused his portion to be exempted, when he adds to it, it is not liable, based on the principle explained above. The Ra'avad differs and maintains that there is an obligation to separate challah from both doughs. For just as the mitzvah of challah is not considered as relating to the Jew's dough, it also does not relate to the gentile's dough. Hence, when he adds to it after his conversion, the obligation takes effect. The Radbaz and the Kessef Mishneh favor the Rambam's understanding and it is quoted as halachah by Shulchan Aruch (Yoreh De'ah 330:6).

הַנּוֹטֵל שְׂאוֹר מֵעִסָּה שֶׁלֹּא הוּרְמָה חַלָּתָהּ וּנְתָנוֹ לְתוֹךְ עִסָּה שֶׁהוּרְמָה חַלָּתָהּ הֲרֵי זֶה מֵבִיא עִסָּה שְׁנִיָּה שֶׁיִּהְיֶה בָּהּ עִם שְׂאוֹר זֶה שִׁעוּר עִסָּה שֶׁחַיֶּבֶת בְּחַלָּה וְנוֹתְנָהּ בְּתוֹךְ הָעִסָּה שֶׁהוּרְמָה חַלָּתָהּ. וּמַפְרֵשׁ מִן הָעִסָּה הַשְּׁנִיָּה שִׁעוּר חַלָּה עָלֶיהָ וְעַל הַשְּׂאוֹר כְּדֵי שֶׁיִּטּל מִן הַמֻּקָּף. וְאִם אֵין לוֹ עִסָּה שְׁנִיָּה נַעֲשֵׂית זוֹ כֻּלָּהּ טֶבֶל וּמַפְרִישׁ חַלָּה עַל הַכּל שֶׁהַטֶּבֶל בְּמִינוֹ אוֹסֵר בְּכָל שֶׁהוּא:

[The following laws apply when a person] takes yeast from a dough from which challah was not separated and places it in a dough from which challah was separated. He should bring a second dough that - together with this yeast - will comprise a measure that obligates the separation of challah and combine it with the dough from which challah was separated.This is preferable to separating challah from the dough with which the yeast was mixed, because a) it will represent a saving for the person separating the challah, since he will not be separating challah a second time; b) it is not desirable to separate challah from the first dough, because the obligation to separate challah from it is Rabbinic, not Scriptural, as will be explained. He should then separate from the second dough the appropriate measure of challah for it and for the yeast. [In this manner,] he is separating [challah] from [dough] that is in the same place.As is required (Chapter 5, Halachah 14). That is why the second dough must be combined with the first dough into which the yeast was placed. If he does not have a second dough, the entire [first dough] is considered as tevel. He should separate challah for the entire amount.The combination of the yeast and the dough. [The rationale is that] when tevelThe yeast. is mixed with its own type,And yeast and dough are considered of the same type. even the slightest amount causes the mixture to become forbidden.This is a Rabbinic decree, according to Scriptural Law, the presence of tevel is also nullified when there is a majority of permitted substances. Our Sages considered tevel as a devar sheyeish lo matirin, a prohibition that could be released, since once the necessary separations are made, the prohibition no longer exists. See Hilchot Ma'achalot Assurot 15:6. Hence, he is not considered to be separating challah from dough that is obligated for that which is exempt (Siftei Cohen 324:20).

עִסָּה הַטְּבוּלָה לְחַלָּה אֵינָהּ כְּחַלָּה. וַהֲרֵי הִיא כְּחֻלִּין לְעִנְיַן הַטֻּמְאָה. שֶּׁאֵין הַשֵּׁנִי עוֹשֶׂה שְׁלִישִׁי בְּחֻלִּין כְּמוֹ שֶׁיִּתְבָּאֵר בִּמְקוֹמוֹ. וּמֻתָּר לִגְרֹם טֻמְאָה לְחֻלִּין שֶׁבְּאֶרֶץ יִשְׂרָאֵל. לְפִיכָךְ שְׁתֵּי עִסּוֹת אַחַת טְמֵאָה וְאַחַת טְהוֹרָה נוֹטֵל כְּדֵי חַלַּת שְׁתֵּיהֶם מֵעִסָּה שֶׁלֹּא הוּרְמָה חַלָּתָהּ וְנוֹתְנוֹ בָּאֶמְצַע סָמוּךְ לָעִסָּה הַטְּהוֹרָה וּמוֹשֵׁךְ מִן הַטְּמֵאָה לַטְּהוֹרָה כְּדֵי בֵּיצָה כְּדֵי לִתְרֹם מִן הַמֻּקָּף:

A dough from which challah has not been separated is like ordinary produce and not like challah with regard to the laws of ritual purity. As will be explained in the appropriate place,Hilchot Sha'ar Avot HaTuma'ah 11:2, 15. impurity of the second degree does not bring about impurity of the third degree with regard to ordinary produce.It does, however, have such an effect with regard to terumah and challah.
It is permitted to cause ordinary produce to contract ritual impurity in Eretz Yisrael.See Hilchot Tuma'at Ochalin 16:9. There the Rambam differentiates between produce from which the appropriate agricultural separations have been made and produce from which they have not been made (as in the present instance). If the separations have already been made, one may bring it into direct contact with ritual impurity. If they have not been made, one may only "cause it to contract ritual impurity," i.e., indirectly. Therefore when there are two doughs, one that is ritually impure and one that is ritually pure, one may take [a portion of dough]Which is ritually pure. equivalent to the measure of challah to be separated from both of them from a dough from which challah was not separated and place it in the center close to the pure dough. He should then extend a portion of the impure dough the size of an eggChallah 2:8 gives this suggestion, but speaks of taking less than the size of an egg of the impure dough, for in that manner, the other dough will not become impure. to the pure doughCausing it to touch it. This will cause the pure dough to become ritually impure (see Hilchot Tuma'at Ochalin 6:18). Nevertheless, this is not significant, because - as the Rambam stated - there is no prohibition against causing food to become ritually impure. so that he will be able to separate challahThe dough set aside to be separated as challah does not become ritually impure, because until it becomes consecrated as challah, it does not become impure because it was touched by dough that was impure to the second degree. And before it is consecrated as challah, it is lifted up and no longer in contact with the source of ritual impurity. To clarify this, the Rambam began this halachah: "A dough from which challah has not been separated is like ordinary produce and... impurity of the second degree does not bring about impurity of the third degree with regard to ordinary produce" (Radbaz). from the dough in the same place.Ordinarily to separate challah for two doughs in the same place, it is not necessary for them to touch. Nevertheless, since one should not separate challah from dough that is ritually pure for dough that is ritually impure (Chapter 5, Halachah 14), in this instance, they must be touching.
The Ra'avad objects to the Rambam's ruling, based on Challah 2:8, but the Radbaz explains the Rambam's position as above.

עוֹשֶׂה אָדָם עִסָּה טְהוֹרָה וְאֵינוֹ מַפְרִישׁ חַלָּתָהּ וּמַנִּיחָהּ אוֹ מַנִּיחַ מִקְּצָתָהּ לִהְיוֹת מַפְרִישׁ עָלֶיהָ וְהוֹלֵךְ חַלּוֹת שֶׁל עִסּוֹת אֲחֵרוֹת. וַאֲפִילוּ נִטְמְאוּ הָעִסּוֹת עַד שֶׁתֵּעָשֶׂה הָעִסָּה שֶׁהִנִּיחַ כֻּלָּהּ חַלָּה וְיִתְּנֶנָּה לַכֹּהֵן. וְהוּא שֶׁלֹּא תִּפָּסֵל מֵאֹכֶל אָדָם. אֲבָל מִשֶּׁתִּסְרַח אֵינוֹ מַפְרִישׁ עָלֶיהָ. בַּמֶּה דְּבָרִים אֲמוּרִים כְּשֶׁהָיוּ אוֹתָם הָעִסּוֹת שֶׁמַּפְרִישׁ עֲלֵיהֶן סָפֵק אִם הוּרְמָה חַלָּה מֵהֶן אוֹ לֹא הוּרְמָה שֶׁחַלַּת דְּמַאי נִטֶּלֶת מִן הַטָּהוֹר עַל הַטָּמֵא לְכַתְּחִלָּה וְשֶׁלֹּא מִן הַמֻּקָּף:

A person may make a pure dough and refrain from separating challah from it, setting it - or a portion of it - aside to continuously separate challot from other doughs with it until the dough set aside becomes challah in its entirety,I.e., the person would consider an appropriate portion of the dough set aside as challah for a given dough and would continue doing this for future doughs until the entire dough that was set aside became challah [the Rambam's Commentary to the Mishnah (Challah 4:6)]. provided [the dough set aside] does not become spoiled to the point that it is no longer fit for human consumption. [This applies] even if the doughs became impure. Once the dough is no longer fit for human consumption, [challah] cannot be separated with it.
When does the above apply? When there is a question whether or not challah has been separated from the doughs for which he is separating challah.E.g., two witnesses stated that challah had been separated from the dough and two other witnesses state that it was not separated. [The rationale is that] challah of a doubtful statusHere the demai is being used differently than its ordinary meaning. For unlike the tithes, it is taken for granted that the common people separate challah just as they separate terumah (Radbaz; see Chapter 8, Halachah 14). may be taken from the pure dough for the impure as an initial preferenceGenerally, the initial preference is not to separate challah from dough that is ritually pure for dough that is ritually impure (Chapter 5, Halachah 14). and the two need not be in the same place.And generally, they must (ibid.).