זמנים
הלכות חמץ ומצה
פרק ה

Halacha

הלכה א
אֵין אָסוּר מִשּׁוּם חָמֵץ בְּפֶסַח אֶלָּא חֲמֵשֶׁת מִינֵי דָּגָן בִּלְבַד. וְהֵם שְׁנֵי מִינֵי חִטִּים שֶׁהֵן הַחִטָּה וְהַכֻּסֶּמֶת. וּשְׁלֹשָׁה מִינֵי הַשְּׂעוֹרִים שֶׁהֵן הַשְּׂעוֹרָה וְשִׁבּלֶת שׁוּעָל וְהַשִּׁפּוֹן. אֲבָל קִטְנִיּוֹת כְּגוֹן אֹרֶז וְדֹחַן וּפוֹלִים וַעֲדָשִׁים וְכַיּוֹצֵא בָּהֶן אֵין בָּהֶן מִשּׁוּם חָמֵץ אֶלָּא אֲפִלּוּ לָשׁ קֶמַח אֹרֶז וְכַיּוֹצֵא בּוֹ בְּרוֹתְחִין וְכִסָּהוּ בִּבְגָדִים עַד שֶׁנִּתְפַּח כְּמוֹ בָּצֵק שֶׁהֶחֱמִיץ הֲרֵי זֶה מֻתָּר בַּאֲכִילָה שֶׁאֵין זֶה חִמּוּץ אֶלָּא סֵרָחוֹן:
כסף משנה
1.
The prohibition against chametz applies only to the five species of grain. They include two species of wheat: wheat and spelt; and three species of barley: barley, oats, and rye.
However, kitniyot - e.g., rice, millet, beans, lentils and the like - do not become leavened. Even if one kneads rice flour or the like with boiling water and covers it with fabric until it rises like dough that has become leavened, it is permitted to be eaten. This is not leavening, but rather the decay [of the flour].

הלכה ב
חֲמֵשֶׁת מִינֵי דָּגָן אֵלּוּ אִם לָשָׁן בְּמֵי פֵּרוֹת בִּלְבַד בְּלֹא שׁוּם מַיִם לְעוֹלָם אֵין בָּאִין לִידֵי חִמּוּץ אֶלָּא אֲפִלּוּ הִנִּיחָן כָּל הַיּוֹם עַד שֶׁנִּתְפַּח הַבָּצֵק מֻתָּר בַּאֲכִילָה [ג.] שֶׁאֵין מֵי פֵּרוֹת מַחְמִיצִין אֶלָּא מַסְרִיחִין. וּמֵי פֵּרוֹת הֵן כְּגוֹן יַיִן וְחָלָב וּדְבַשׁ וְשֶׁמֶן זַיִת וּמֵי תַּפּוּחִים וּמֵי רִמּוֹנִים וְכָל כַּיּוֹצֵא בָּהֶן מִשְּׁאָר יֵינוֹת וּשְׁמָנִים וּמַשְׁקִין. וְהוּא שֶׁלֹּא יִתְעָרֵב בָּהֶן שׁוּם מַיִם בָּעוֹלָם. וְאִם נִתְעָרֵב בָּהֶן מַיִם כָּל שֶׁהוּא הֲרֵי אֵלּוּ מַחְמִיצִין:
כסף משנה
2.
With regard to these five species of grain: If [flour from these species] is kneaded with fruit juice alone1מי פירות literally means "the water of fruit." However, as the halachah explains, the practical application of the term is much broader. without any water, it will never become leavened. Even if [flour] is placed in [these juices] the entire day until the dough rises, it is permitted to be eaten [on Pesach],2This halachah is a matter of controversy among the commentators. In his commentary on the Mishnah (Pesachim 3:1), the Rambam makes similar statements. However, in the Oxford manuscript of that text, the words "permitted to be eaten" are crossed out and replaced with the words "one is not obligated for כרת." However, it appears that this emendation was made by Rav Avraham, the Rambam's son, and not the Rambam himself.
The Shulchan Aruch (Orach Chayim 462:1) permits the use of fruit juice. However, the Ramah (462:4) states that it is Ashkenazic custom not to use fruit juice for matzah on Pesach out of the fear that some water might perhaps be mixed together with it (see below). Nevertheless, he does allow leniency for people who are ill or sick and have difficulty eating normal matzah.
Among the present day applications of this concept is commercially produced "egg matzah." According to the above guidelines, in the Ashkenazic community, such matzah:a) cannot be used in the Seder, as explained in the commentary to Halachah 6:2;
b) must contain only eggs and fruit juice, with no water whatsoever;
c) even so, should be eaten only by those with medical problems that prevent them from eating normal matzah.
for fruit juice does not cause [dough] to become leavened.3and thus become chametz. Rather, It merely causes [the flour] to decay.4Nevertheless, dried out wine dregs which have fermented do cause the dough to become leavened (Tosefot, Pesachim 28b).
The following are [included in the category] of fruit juice: wine, milk, honey,5The Hagahot Maimoni explains that this applies to both bee and date honey. olive oil, apple juice,6The dough is permitted even if the apple juice has begun to ferment. pomegranate juice and all other similar wines, oils, and beverages.7Shulchan Aruch HaRav (Orach Chayim 462:2) defines מי פירות as: "any liquid that is not derived from water... even if it does not come from produce."
This applies so long as no water whatsoever is mixed with them. If any water is mixed with them, they cause [the flour] to become leavened.8Indeed, when water is mixed with these juices, the dough becomes leavened much faster than if it had been mixed with water alone. Generally, dough can be left eighteen minutes before it becomes leavened, but the limit for dough made from a mixture of these liquids and water is much less (Shulchan Aruch, Orach Chayim 462:2). See commentary to Halachah 20.

הלכה ג
אֵין מְבַשְּׁלִין חִטִּים בְּמַיִם כְּגוֹן רִיפוֹת וְלֹא קֶמַח כְּגוֹן לְבִיבוֹת. וְאִם בִּשֵּׁל הֲרֵי זֶה חָמֵץ גָּמוּר וְהוּא שֶׁיִּתְבַּקְּעוּ בַּתַּבְשִׁיל. אֵין קוֹלִין אֶת הַבָּצֵק בְּשֶׁמֶן עַל הַמַּחֲבַת. אֲבָל מְבַשְּׁלִין אֶת הַפַּת וְאֶת הַקֶּמַח הַקָּלוּי. וְאִם הִרְתִּיחַ הַמַּיִם הַרְבֵּה וְאַחַר כָּךְ הִשְׁלִיךְ לְתוֹכָן הַקֶּמַח הֲרֵי זֶה מֻתָּר מִפְּנֵי שֶׁהוּא מִתְבַּשֵּׁל מִיָּד קֹדֶם שֶׁיַּחְמִיץ. וּכְבָר נָהֲגוּ בְּשִׁנְעָר וּבִסְפָרַד וּבְכָל הַמַּעֲרָב לֶאֱסֹר דָּבָר זֶה גְּזֵרָה שֶׁמָּא לֹא יַרְתִּיחַ הַמַּיִם יָפֶה יָפֶה:
כסף משנה
3.
[On Pesach,] we should not cook wheat in water1Though raw wheat itself is not chametz, once wheat or flour is mixed with water, it becomes leavened within eighteen to twenty-four minutes. (See Halachah 12.) Less time is required when heat is applied to it. Hence, cooking or baking with wheat or flour on Pesach must be carried out under careful guidelines. - for example, cracked wheat2wheat served as a grain. - or flour [in water] - for example, dough balls.3A dish resembling kneidlach, but made with regular flour rather than matzah meal. If one cooks [either of the above]4behold, it is absolutely chametz - for the wheat or flour has become leavened. - behold, it is absolutely chametz. This applies5This clause obviously refers only to cooking wheat. if [the kernels] crack open within the dish.6the cracking open of the kernels is a sign that the wheat has expanded because of leavening.
We may not fry dough7made with water in oil in a frying pan.8The Maggid Mishneh explains that oil is considered מי פירות and, hence, will cause the dough to become leavened. (See also Nodah BiYhudah, Vol. II, Responsum 57.) However, we may cook a loaf [of matzah]9Pesachim 39b states that once matzah has been baked, it can be cooked again without the fear of leavening. Similarly, it can be ground into meal, and then used as flour without the fear of becoming chametz. (See also Shulchan Aruch, Orach Chayim 463:3.)
This law is the basis of the widely practiced leniency of cooking and baking with matzah meal. Nevertheless, certain Ashkenazic communities refrain from using matzah meal because of the custom of שרויה, gebruks. Rav Shneur Zalman of Liadi (Responsum VI; see also Sha'arei Teshuvah, Orach Chayim 460:10) writes that it is possible that some of the dough was not baked thoroughly and some flour remaining in it could become chametz when cooked again.
or roasted flour.10Once flour has become roasted, it will not become leavened. However, we must differentiate between roasted flour and flour made from roasted wheat; the latter flour may not be used on Pesach. (See Halachah 5.) The Pri Chadash even questions the leniency of using roasted flour. If one boiled a lot of water and, afterwards, placed flour into it11behold, it is permitted because it -- the flour - behold, it is permitted, because it is cooked immediately, before it could become leaven.12This practice was permitted only when the water was absolutely boiling at the time the flour was placed in it. [Nevertheless,] it is accepted custom in Babylonia, Spain, and the entire western [diaspora] to forbid this practice. This has been decreed lest one not boil the water well enough.13The Shulchan Aruch (Orach Chayim 454:3) states: "At present, there are none who know how to boil foods in this manner. Hence, all boiling is forbidden."

הלכה ד
מֻתָּר לְבַשֵּׁל הַדָּגָן אוֹ הַקֶּמַח בְּמֵי פֵּרוֹת. וְכֵן בָּצֵק שֶׁלָּשׁוֹ בְּמֵי פֵּרוֹת אִם בִּשְּׁלוֹ בְּמֵי פֵּרוֹת אוֹ קָלָהוּ עַל הַמַּחֲבַת בְּשֶׁמֶן הֲרֵי זֶה מֻתָּר שֶׁמֵּי פֵּרוֹת אֵינָן מַחְמִיצִין:
כסף משנה
4.
It is permissible to cook grain or flour in fruit juice.1Baking dough kneaded with מי פירות was discussed in Halachah 2. The present halachah explains that flour mixed with those liquids will not become leavened even when cooked or fried. Thus, dough which was kneaded with fruit juice, cooked with fruit juice, or fried with oil in a frying pan is permitted, for fruit juice does not cause leavening.2As explained above, it is Ashkenazic custom not to use dough or flour cooked with these liquids.

הלכה ה
כַּרְמֶל שֶׁמְּהַבְהֲבִין אוֹתוֹ בָּאוּר וְטוֹחֲנִין אוֹתוֹ אֵין מְבַשְּׁלִין אֶת הַקֶּמַח שֶׁלּוֹ בְּמַיִם שֶׁמָּא לֹא נִקְלָה בָּאוּר יָפֶה וְנִמְצָא מַחֲמִיץ כְּשֶׁמְּבַשְּׁלִין אוֹתוֹ. וְכֵן כְּשֶׁמּוֹלְלִין הַקְּדֵרוֹת הַחֲדָשׁוֹת אֵין מְבַשְּׁלִין בָּהֶן אֶלָּא מַצָּה אֲפוּיָה שֶׁחָזְרוּ וְטָחֲנוּ אוֹתָהּ אֲבָל קֶמַח קָלִי אָסוּר שֶׁמָּא לֹא קָלָהוּ יָפֶה וְיָבוֹא לִידֵי חִמּוּץ:
כסף משנה
5.
Roasted grain1Once wheat is roasted, flour that is made from it will never become leavened. which is singed in fire2lightly roasted in order to dry out any moisture. and then ground [into flour]: That flour should not be cooked with water, lest it has not been roasted well in the fire, and thus will become leavened when cooked.3Rabbenu Manoach explains that this law applies only to light roasting. If grain is roasted thoroughly, its flour may be used. However, in instances of this nature, the Rabbis would rather forbid such practices entirely than allow a loosely defined leniency. (See Shulchan Aruch, Orach Chayim 463:3.)
Similarly, when preparing new pots,4מלל, the word used by the Rambam, means "husk." In his dictionary, Rabbenu Tanchum of Jerusalem explains the derivation of this term:
They take fresh barley, singe it, dry it, and grind it into flour. Afterwards, it is cooked until it is soft... and then, it is poured into new pots to reduce their porosity.
In his commentary on the Mishneh Torah, Rav Kapach notes that such practices are still followed in Yemen today.
we should not cook in them anything other than matzah that was baked and then ground into flour.5matzah meal. As explained in Halachah 4, once matzah has been baked, it will never become leavened. It is forbidden to do so with roasted flour, for perhaps it will not be roasted well, and thus may become leaven.6This statement is slightly problematic, for Halachah 4 mentioned that we may cook with roasted flour.

הלכה ו
אֵין בּוֹלְלִין אֶת הַשְּׂעוֹרִין בְּמַיִם בְּפֶסַח מִפְּנֵי שֶׁהֵן רָפִין וּמַחְמִיצִין בִּמְהֵרָה. וְאִם בָּלַל אִם רָפוּ כְּדֵי שֶׁאִם הִנִּיחָן עַל פִּי הַבִּיב שֶׁאוֹפִין עָלָיו הַחַלּוֹת יִתְבַּקְּעוּ הֲרֵי אֵלּוּ אֲסוּרִין. וְאִם לֹא הִגִּיעוּ לְרִפְיוֹן זֶה הֲרֵי אֵלּוּ מֻתָּרִין:
כסף משנה
6.
We do not stir barley in water on Pesach [to remove its husks],1Rabbenu Manoach explains that the kernels of grain were placed in hot water, stirred vigorously, and then crushed to remove the husks. because [the kernels] are soft and become leavened rapidly. If one did stir [barley] in water and [the kernels] softened to the point2The cracking open of the kernels would be the clearest sign that the grain had become leavened. However, even if the leavening process has reached the point that if they were placed at the opening to a roasting pan3Our translation of ביב follows Rav Yitzchak Alfasi and Rabbenu Chanan'el. See also Halachah 22. However, Rashi (Pesachim 40a) provides a different and more lenient interpretation. upon which loaves were usually baked, they would burst open - behold, they are forbidden.4This is a very stringent measure. Once barley kernels are exposed to water, they will burst open shortly after being exposed to heat of this nature. If they have not reached this degree of softness, they are permitted.

הלכה ז
הַחִטִּים מֻתָּר לִבְלל אוֹתָן בְּמַיִם כְּדֵי לְהָסִיר סֻבָּן וְטוֹחֲנִין אוֹתָן מִיָּד כְּדֶרֶךְ שֶׁטּוֹחֲנִין הַסּלֶת. וּכְבָר נָהֲגוּ כָּל יִשְׂרָאֵל בְּשִׁנְעָר וּבְאֶרֶץ הַצְּבִי וּבִסְפָרַד וּבְעָרֵי הַמַּעֲרָב שֶׁלֹּא יִבְלְלוּ הַחִטִּים בְּמַיִם גְּזֵרָה שֶׁמָּא יִשְׁהוּ וְיַחֲמִיצוּ:
כסף משנה
7.
It is permissible to stir wheat [kernels] in water to remove the bran,1Wheat kernels are firmer than barley kernels. and then immediately2Once the grain has come in contact with water and it is left untended for the time it takes a person to walk a mil, it will become leavened. (See Shulchan Aruch, Orach Chayim 467:2.) grind them, as is done when grinding fine flour.3The commentaries note that in Hilchot Ma'aseh HaKorbanot 12:20, the Rambam states that the grain used for the meal offerings was not stirred in water, lest it become leavened. Among the resolutions offered to this difficulty is that chametz is a severe prohibition, and greater care would be taken. [Nevertheless,] all Jews in Babylonia, Eretz Yisrael,4Gittin 57a explains why the term ארץ צבי is used as a reference for Eretz Yisrael. Spain, and the cities of the western [diaspora] have accepted the custom of not stirring wheat in water.5Rabbenu Manoach mentions that this custom was several hundred years old in his time (approx. 1200 CE). Pesachim 40a mentions that even in Talmudic times, a בעל נפש (a person precise in the observance of the commandments) would not use wheat that had been stirred. The Shulchan Aruch (Orach Chayim 453:5) states that stirring wheat is "prohibited." This decree [was instituted] lest [the kernels] be left aside and become leavened.6i.e., the fear is not that the wheat will become leavened while the bran is being removed, but rather, that after it has been removed, it will be left to become leavened.

הלכה ח
תַּבְשִׁיל שֶׁנִתְבַּשֵּׁל וְנִמְצְאוּ בּוֹ שְׂעוֹרִים אוֹ חִטִּים אִם נִתְבַּקְּעוּ הֲרֵי כָּל הַתַּבְשִׁיל אָסוּר שֶׁהֲרֵי נִתְעָרֵב בּוֹ הֶחָמֵץ. וְאִם לֹא נִתְבַּקְּעוּ מוֹצִיאִין אוֹתָן וְשׂוֹרְפָן וְאוֹכְלִין שְׁאָר הַתַּבְשִׁיל. שֶׁאֵין הַדָּגָן שֶׁנִּבְלַל וְלֹא נִתְבַּקֵּעַ חָמֵץ גָּמוּר שֶׁל תּוֹרָה. וְאֵינוֹ אֶלָּא מִדִּבְרֵי סוֹפְרִים:
כסף משנה
8.
A dish that was cooked, and barley or wheat1Some authorities recommend more severe laws for wheat than for barley, but the Rambam equates the two. was discovered inside it:2One kernel of grain can create difficulties, for even the slightest amount of chametz that is mixed together with other foods causes them to be forbidden (Halachah 5 above). If the grains have cracked open,3they have surely become chametz. Hence, the entire dish is forbidden, for chametz has become mixed together with it.4Furthermore, the pot and utensils with which it was cooked are also forbidden during Pesach. If they have not cracked open,5Halachah 6 above mentions a more severe measure. However, that ruling concerns the kernels of grain themselves, while our law deals with their effect on another dish, which is merely a Rabbinic ordinance. Hence, greater leniency is shown (Maggid Mishneh). they6the barley or wheat itself must be removed and burned,7as if they were chametz but the remainder of the dish may be eaten.8The Shulchan Aruch (Orach Chayim 467:9) accepts this ruling. However, the Ramah and the other major Ashkenazic authorities forbid use of this dish. However, the Taz allows the dish to be sold to a gentile. [This ruling was given] because grain that has been stirred in water without cracking open is not actual leaven as forbidden by the Torah. It is only a Rabbinic [ordinance].

הלכה ט
מִשּׁוּם שֶׁנֶּאֱמַר (שמות יב יז) "וּשְׁמַרְתֶּם אֶת הַמַּצּוֹת" כְּלוֹמַר הִזָּהֲרוּ בַּמַּצָּה וְשִׁמְרוּ אוֹתָהּ מִכָּל צַד חִמּוּץ. לְפִיכָךְ אָמְרוּ חֲכָמִים צָרִיךְ אָדָם לִזָּהֵר בְּדָגָן שֶׁאוֹכֵל מִמֶּנּוּ בַּפֶּסַח שֶׁלֹּא יָבוֹא עָלָיו מַיִם אַחַר שֶׁנִּקְצַר עַד שֶׁלֹּא יִהְיֶה בּוֹ שׁוּם חִמּוּץ. דָּגָן שֶׁנִּטְבַּע בַּנָּהָר אוֹ שֶׁנָּפַל עָלָיו מַיִם כְּשֵׁם שֶׁאָסוּר לְאָכְלוֹ כָּךְ אָסוּר לְקַיְּמוֹ אֶלָּא מוֹכְרוֹ לְיִשְׂרָאֵל וּמוֹדִיעוֹ כְּדֵי שֶׁיֹּאכְלֶנּוּ קֹדֶם הַפֶּסַח. וְאִם מְכָרוֹ לְנָכְרִי קֹדֶם הַפֶּסַח מוֹכֵר מְעַט לְכָל אֶחָד וְאֶחָד כְּדֵי שֶׁיִּכְלֶה קֹדֶם הַפֶּסַח שֶׁמָּא יַחֲזֹר הַנָּכְרִי וְיִמְכְּרֶנּוּ לְיִשְׂרָאֵל:
כסף משנה
9.
[Exodus 12:17] states: "Keep watch over the matzot"1Some ancient manuscripts of the Mishneh Torah include these two lines in the previous halachah, but all published texts follow this division. - i.e., be careful of the matzot and protect them from any possibility of becoming chametz.2Furthermore, as evident from Halachah 6:5, this verse also implies that the flour and the matzot made from it must be watched with the specific intent that they be used for the mitzvah of eating matzah on Pesach.
The above is the source for the practice of eating shemurah matzah, matzah made from grain which has been watched to ensure that it did not become chametz and prepared with the intent that it be used for the mitzvah of eating matzah. The use of such matzah during the Seder is an absolute requirement (Shulchan Aruch, Orach Chayim 460), and it is advisable to use it throughout the holiday.
Therefore, our Sages declared: A person must be careful regarding the grain which he eats on Pesach3Pesachim 40a relates that Ravvah would tell the harvesters cutting wheat for Pesach: "Have the intent that this grain be used for the mitzvah of matzah." and [make sure] that no water has come in contact with it4The chronicles of Jewish community life in both Eastern Europe and North Africa relate how the harvest of the wheat used for matzah was always begun at noontime, long after the morning dew had risen. after it has been harvested,5Based on the above passage from Pesachim, Rav Yitzchak Alfasi and the Rambam require that the grain be watched from the time of harvesting onward. Nevertheless, Rabbenu Asher follows a more lenient policy and does not require the wheat to be watched until it is ground. [Rabbenu Nissim explains that even Rav Yitzchak Alfasi only recommended watching the matzah from harvesting as a pious measure, and not as an absolute rule.]
The Shulchan Aruch (Orach Chayim 453:4) explains that it is preferable to use grain that has been watched from harvesting; as a minimum requirement, one must use grain that has been watched from the time it has been ground into flour. If there is no other alternative, one may buy flour in the marketplace and begin watching from the time the dough is kneaded.
The Mishnah Berurah clarifies the latter point explaining that where grain is washed or submerged in water before grinding it into flour, such grain may not be used for matzah. (This practice is still common in many communities.) In practice, most shemurah matzah made at present is watched from the time the grain was harvested.
so that it will not have become chametz at all.6However, before the grain is cut, no precautions are ordinarily necessary. Nevertheless, the Shulchan Aruch (Orach Chayim 467:5) mentions that if the wheat kernels have dried out and no longer need nurture from the land, they can become chametz.
Grain which sunk in a river or7Pesachim 40b mentions a ship which sank carrying a cargo of wheat. After the ship was recovered, Ravvah allowed the wheat to be sold. From that example, we can derive concepts governing all instances where grain came in contact with water,8Rabbenu Manoach emphasizes that this halachah applies to wheat kernels that have not split open. Had they split open, a Jewish purchaser would immediately notice the fact and there would be no need to inform him. just as it is forbidden to eat from it [on Pesach], it is forbidden to keep [possession of] it.9Halachah 7 mentioned that one could stir wheat in water to remove the husks without it becoming chametz. Since the wheat was constantly being agitated, it would not become leavened. In contrast, this halachah contains a more stringent ruling, for the grain was left at rest (Tzafnat Paneach). Rather, he should10preferably sell it to a Jew11and not a gentile [before it becomes prohibited]12after the fifth hour on the fourteenth of Nisan and inform him [about its nature], so that he can eat it before Pesach.13If he does not inform him, it would be forbidden to sell the chametz to him, lest he keep possession of it on Pesach, and thus violate the commandment against owning chametz. If he sells it to a gentile before Pesach, he should sell a small amount to a number of individuals,14Most texts of Pesachim (ibid.) read: "He should sell small amounts to Jews." Apparently, the Rambam's text of the Talmud did not contain that phrase. If a Jew knows that the grain has become leavened, he will surely take the necessary precautions so that it will not remain in his possession on Pesach. so that it will be finished before Pesach, lest the gentile go and sell it to [another] Jew.15The later authorities (see Mishnah Berurah 467:3) question what to do if large amounts of grain come into contact with water on Erev Pesach, when it is not possible for the gentile to consume the entire amount before Pesach. They advise that it be sold to a gentile who will surely sell it back to the Jew after the holiday.

הלכה י
דָּגָן שֶׁנָּפַל עָלָיו דֶּלֶף כָּל זְמַן שֶׁהוּא טוֹרֵד טִפָּה אַחַר טִפָּה אֲפִלּוּ כָּל הַיּוֹם כֻּלּוֹ אֵינוֹ בָּא לִידֵי חִמּוּץ. אֲבָל כְּשֶׁיִּפָּסֵק אִם נִשְׁתַּהָה כַּשִּׁעוּר הֲרֵי זֶה אָסוּר:
כסף משנה
10.
Grain1Most texts of Pesachim 39b, the source for this law, read "flour" instead of "grain." Similarly, when quoting this law, the Shulchan Aruch (Orach Chayim 466:6) also states "flour." upon which [water] leaking [from the roof] has fallen: As long as [the leak] continues, drop after drop, it will not become chametz2The dripping of the water agitates the grain and prevents it from becoming chametz. even if [the leak continues] the entire day.3However, the grain must be made into flour and baked immediately after being taken from under the leak. Otherwise, it will become leavened (Shulchan Aruch). However, if [the leak] stops,4or the grain is moved if it remains [untouched] for the standard measure [of time]5the time it takes a person to walk a mil, as explained in Halachah 13 - behold, it becomes chametz.

הלכה יא
אֵין לָשִׁין בְּפֶסַח עִסָּה גְּדוֹלָה שֶׁמָּא תַּחֲמִיץ אֶלָּא כְּשִׁעוּר חַלָּה בִּלְבַד. וְאֵין לָשִׁין לֹא בְּחַמִּין וְלֹא בְּחַמֵּי חַמָּה. וְלֹא בְּמַיִם שֶׁנִּשְׁאֲבוּ בּוֹ בַּיּוֹם אֶלָּא בְּמַיִם שֶׁלָּנוּ. וְאִם עָבַר וְלָשׁ בְּאֶחָד מִכָּל אֵלּוּ הֲרֵי הַפַּת אֲסוּרָה:
כסף משנה
11.
We do not knead a large dough on Pesach, lest it become chametz.1Pesachim 48b relates that dough will not become chametz as long as it is being kneaded. However, a large dough is hard to manage. Hence, our Sages restricted a dough's size to insure that women kneading it will be able to continually agitate the entire dough.
The Rokeach mentioned that in his age, baking conditions had changed from Talmudic times. More people were involved in the process and the ovens were larger and baked matzot more quickly. Therefore, leniency was taken as regards the restriction of the size of the dough. However, the Shulchan Aruch HaRav and the Mishnah Berurah both recommend adhering to the former practice.
Rather, [the size of the dough] is confined to the measure for which one is obligated to separate Challah.2and a fifth eggs, as stated in the following halachah; approximately 73 fluid ounces, 9.125 cups, or 131.8 cubic inches in contemporary measure.
We do not knead with hot water, with water heated in the sun, or with water that was drawn on the present day,3Rashi (Pesachim 42a) relates that the position of the sun in the spring causes the temperature of well and spring water to rise. Hence, matzah may be kneaded only with water that has4been drawn [preferably, either slightly before or directly after sunset on the day before the matzot are to be baked (Shulchan Aruch, Orach Chayim 455:1)], and rested for a day. A person who violates [this requirement] and kneads using one of the above5types of water whose use the Sages forbade; - behold, the [baked] loaf becomes forbidden.6There is no debate about the prohibition against using hot water. However, with regard to the prohibition against using water drawn that day, the Shulchan Aruch (455:3) quotes the Rambam's opinion, but states that in a difficult situation, one may use matzah that was inadvertently kneaded with water that was not drawn on the previous day. The Ramah and the Ashkenazic authorities are more lenient and allow the use of such matzah in all situations.

הלכה יב
לֹא תֵּשֵׁב אִשָּׁה תַּחַת הַשֶּׁמֶשׁ וְתָלוּשׁ. וְלֹא תַּחַת הָרָקִיעַ בְּיוֹם הֶעָבִים אֲפִלּוּ בְּמָקוֹם שֶׁאֵין הַשֶּׁמֶשׁ זוֹרַחַת בּוֹ. וְלֹא תָּנִיחַ אֶת הָעִסָּה וְתִתְעַסֵּק בְּדָבָר אַחֵר. וְאִם הָיְתָה לָשָׁה וְאוֹפָה צְרִיכָה שְׁנֵי כֵּלִים שֶׁל מַיִם. אֶחָד שֶׁמְּקַטֶּפֶת בּוֹ וְאֶחָד שֶׁמְּצַנֶּנֶת בּוֹ יָדֶיהָ. וְאִם עָבְרָה וְלָשָׁה תַּחַת הַשֶּׁמֶשׁ אוֹ שֶׁלֹּא צִנְּנָה יָדֶיהָ אוֹ שֶׁעָשְׂתָה עִסָּה יֶתֶר מִשִּׁעוּר חַלָּה הַפַּת מֻתֶּרֶת. וְכַמָּה שִׁעוּר חַלָּה כְּמוֹ שָׁלֹשׁ וְאַרְבָּעִים בֵּיצִים וְחֹמֶשׁ בֵּיצָה כְּגוּף הַבֵּיצָה הַבֵּינוֹנִית לֹא כְּמִשְׁקָלָהּ:
כסף משנה
12.
A woman should not sit in the sun and knead,1lest the sun's heat speed up the leavening process. nor [should she knead] under the open sky on a cloudy day, even in a place where the sun is not shining.2Yoma 28b states: "a cloudy day is all sun; the heat of a cloudy day is more severe than that of a sunny day."
The Ramah (Orach Chayim 459:1) mentions that it is customary not to knead near a window. The Shulchan Aruch states that the kneading area of a bakery should be distant from the baking area, so that the heat of the oven should not affect the dough.
[She should not] leave the dough3The Shulchan Aruch adds "even for a moment." and become involved in another matter.4the dough should not be left unattended. In his commentary on the Mishnah (Pesachim 3:4), the Rambam explains that preferably the preparation and baking of the matzah should be a speedy and uninterrupted process. See also the following halachah. If she both kneads and bakes,5The Sages feared that her hands would become hot from the oven, and thus speed up the leavening process when she kneads the dough. Hence, they required that she must have two containers of water,6the same water should not be used for both activities. one to smooth [the matzot]7Before the matzot are placed in the oven, the woman baking them would dip her hands in cold water and smooth and shape the loaves. and one to cool off her hands.8from the heat of the oven. It must be noted that Rashi (Pesachim 42a) maintains that the activity of kneading the dough itself heats up the hands. Thus, he requires that a woman dip her hands in water between doughs to cool off her hands, even when she is not baking. The Shulchan Aruch (459:3) follows Rashi's interpretation.
If she violated [these instructions] and kneaded dough in the sun,9unless one can actually feel that the temperature of the dough has risen (Magen Avraham 559:15). or did not cool off her hands, or made a dough larger than the measure for which one is obligated to separate Challah, the loaf is permitted.10In these instances, the Sages did not feel that the leavening process would necessarily be speeded up if their instructions were not followed. Hence, בדיעבד (after the fact), they did not prohibit the use of matzot baked in this manner. What is the measure for which one is obligated to separate Challah? Forty-three and a fifth eggs of average size11Rabbenu Manoach notes that the numerical equivalent of Challah (חלה) is also 43. - by volume and not by weight.12A given volume of dough is much heavier than the same volume of eggs.
In Hilchot Bikkurim 6:15, the Rambam elaborates further on this subject, by giving a measure according to weight as well. In modern measure, the figure he gives equals approximately 1.7 kilograms (close to 4 lbs.).

הלכה יג
כָּל זְמַן שֶׁאָדָם עוֹסֵק בַּבָּצֵק אֲפִלּוּ כָּל הַיּוֹם כֻּלּוֹ אֵינוֹ בָּא לִידֵי חִמּוּץ. וְאִם הִגְבִּיהַּ יָדוֹ וֶהֱנִיחוֹ וְשָׁהָה הַבָּצֵק עַד שֶׁהִגִּיעַ לְהַשְׁמִיעַ הַקּוֹל בִּזְמַן שֶׁאָדָם מַכֶּה בְּיָדוֹ עָלָיו כְּבָר הֶחְמִיץ וְיִשָּׂרֵף מִיָּד. וְאִם אֵין קוֹלוֹ נִשְׁמָע אִם שָׁהָה כְּדֵי שֶׁיְּהַלֵּךְ אָדָם מִיל כְּבָר הֶחְמִיץ וְיִשָּׂרֵף מִיָּד. וְכֵן אִם הִכְסִיפוּ פָּנָיו כְּאָדָם שֶׁעָמְדוּ שַׂעֲרוֹתָיו הֲרֵי זֶה אָסוּר לְאָכְלוֹ וְאֵין חַיָּבִין עָלָיו כָּרֵת:
כסף משנה
13.
As long as a person is busy with the dough, even for the entire day, it will not become chametz.1As mentioned previously, as long as the dough is constantly being agitated it will not become leavened. If he lifts up his hand2from kneading and allows the dough to rest so that [it rises to the extent that] a noise will resound when a person claps it with his hand,3The Shulchan Aruch (Orach Chayim 459:2) mentions another sign; the appearance of cracks or folds in the dough. it has already become chametz4even if the time period explained below has not elapsed and must be burned immediately.5The Rambam is describing an instance when matzah is being baked on Pesach eve or during the holiday, when the possession of chametz is forbidden. If a noise does not resound6when the dough is clapped, the possibility still exists that the dough has become chametz. The time the dough has been left unattended is then calculated and7if the dough has lain at rest for the time it takes a man to walk a mil,8two thousand cubits; according to most authorities approximately a kilometer in modern measure. Most authorities (including the Shulchan Aruch and many later Rabbis with regard to halachah l'ma'aseh) define eighteen minutes as the accepted period of time in which an average man would walk this distance. However, the Rambam (Commentary on the Mishnah 3:2) quotes a more lenient figure, 24 minutes. it has become chametz and must be burned immediately.9The Shulchan Aruch and the Ramah suggest hurrying the process of kneading and baking matzah, because:
a) the heat generated by working the dough may cause it to become leavened faster.
b) though each particular hesitation may be less than eighteen minutes, the total of all hesitations may exceed that figure. (This point is not accepted by all authorities.)
c) once dough is left unattended after having been kneaded thoroughly, it will become leavened very quickly.

Similarly, if its surface has become wrinkled10Rabbenu Manoach interprets the Hebrew הכסיפו as "whitened." [to the extent that it resembles] a person whose hair stands [on end in fright]11behold -- this is a sign that the dough has begun to become leavened. Hence, - behold, it is forbidden to eat from it, but one is not liable for כרת [for eating it].12The commentaries question whether the Rambam's intent is to free the person from punishment entirely or whether he means that he is not liable for כרת, but receives a lesser punishment, lashes.

הלכה יד
הָיוּ שְׁתֵּי עִסּוֹת שֶׁהִגְבִּיהוּ הַיָּד מֵהֶן נִלּוֹשׁוֹת בְּעֵת אַחַת וְנִשְׁתַּהוּ. הָאַחַת מֵהֶן יֵשׁ לָהּ קוֹל וְהָאַחֶרֶת אֵין לָהּ קוֹל. שְׁתֵּיהֶן יִשָּׂרְפוּ וַהֲרֵי הֵן חָמֵץ גָּמוּר:
כסף משנה
14.
There were two doughs which people stopped kneading at the same time and left unattended.1for less than the time it takes a person to walk a mil. From one, a sound [resounded when clapped].2a clear sign the dough has become leavened, as stated in the previous halachah. From the other, no sound [resounded].3Nevertheless, since they both waited the same amount of time, we assume that a similar leavening process took place in both doughs. Hence, Both of them should be burned4behold, they are -- considered - behold, they are absolutely chametz.

הלכה טו
אֵין עוֹשִׂין סְרִיקִין הַמְצֻיָּרִין בְּפֶסַח מִפְּנֵי שֶׁהָאִשָּׁה שׁוֹהָה עֲלֵיהֶן וּמִתְחַמְּצִין בְּעֵת עֲשִׂיָּתָן. לְפִיכָךְ הַנַּחְתּוֹמִין מֻתָּרִין לַעֲשׂוֹתָם מִפְּנֵי שֶׁהֵן בְּקִיאִין בְּאֻמָּנוּתָן וּמְמַהֲרִים לַעֲשׂוֹתָם. אֲבָל בַּעֲלֵי בָּתִּים אֲסוּרִים וַאֲפִלּוּ צָרוּ אוֹתָן בִּדְפוּס. שֶׁמָּא יָבוֹאוּ אֲחֵרִים לַעֲשׂוֹתוֹ שֶׁלֹּא בִּדְפוּס וְיִשְׁהוּ בַּעֲשִׂיָּתָן וְיַחֲמִיצוּ:
כסף משנה
15.
We should not make thick loaves1Pesachim 37a allows thin loaves to be made with designs. Commenting on this statement, the Ramah (Orach Chayim 460:4) suggests never making thick matzot for Pesach. with designs2Rav Yitzchak ibn Giat writes that it was customary to make designs of fish, doves, and other animals. on Pesach, because a woman takes time making them.3However, there is no prohibition against making holes in their dough as is the common practice. On the contrary, this helps the matzah bake faster (Shulchan Aruch). Thus, [the dough] will become leavened during that time. Hence, professional bakers are allowed to make [such designs],4Pesachim (ibid.) records that Rabban Gamliel's household used such matzot, and hence was forced to make this differentiation. because they are skilled in their craft and quick in its execution.5Rashi (Pesachim, ibid.) adds that bakers usually have pre-cut forms.
The Mishnah Berurah (Orach Chayim 460:14) forbids all designs, whether made by private people or professional bakers, whether on thick or thin loaves.

[In contrast,] a private person is forbidden to make such a design, even if he does so using a [pre-cut] form.6which will not require time. [This stringency was instituted] lest others attempt to make [the designs] without using the forms, delay in their work, and cause [the dough] to become chametz.7Our Sages often instituted decrees uniformly, even though the reason for the decree did not apply in certain instances, lest people misinterpret the leniency and take total license.

הלכה טז
מַיִם שֶׁרוֹחֲצִין בָּהֶן הַיָּדַיִם וְהָעֲרֵבָה אַחַר שֶׁלָּשִׁין וְכֵן מַיִם שֶׁמִּשְׁתַּמְּשִׁין בָּהֶן בִּשְׁעַת לִישָׁה הֲרֵי זֶה יִשְׁפֹּךְ אוֹתָן בִּמְקוֹם מִדְרוֹן כְּדֵי שֶׁלֹּא יִתְקַבְּצוּ בְּמָקוֹם אֶחָד וְיַחְמִיץ:
כסף משנה
16.
The water used to wash one's hands and the kneading trough after the kneading [is completed]1The Mishnah (Pesachim 40b) uses the expression "water used by a baker." In his commentary on the Mishnah, the Rambam defines that term as above. and, similarly, the water used when kneading2when shaping the dough or cooling off one's hands, as mentioned in Halachah 12. - behold, it should be poured out in a place which slopes downward, so it will not collect in one place3See Pesachim 42a. The Ramah (Orach Chayim 459:4) also gives instructions about cleaning the utensils used in preparing the matzah to ensure that no dough is allowed to remain stuck to them, and thus become chametz. and become leavened.4This halachah applies when matzah is prepared and baked after the prohibition against chametz has gone into effect (Shulchan Aruch). However, some later authorities (Bach, Taz) forbid such water to collect even beforehand.

הלכה יז
אֵין שׁוֹרִין אֶת הַמֻּרְסָן וּמַנִּיחִין לִפְנֵי הַתַּרְנְגוֹלִין שֶׁמָּא יַחְמִיץ. אֲבָל חוֹלְטִין לָהֶן הַמֻּרְסָן בְּרוֹתְחִין וּמַנִּיחִין לִפְנֵיהֶן. וּכְבָר נָהֲגוּ רֹב הָעוֹלָם שֶׁלֹּא לַחֲלֹט גְּזֵרָה שֶׁמָּא לֹא יַרְתִּיחַ הַמַּיִם יָפֶה:
כסף משנה
17.
We should not soak bran1The Mishnah Berurah 454:2 notes that there is a difference of opinion among halachic authorities if מורסן refers to the hard shell of the wheat kernels that falls off when the wheat is ground, or the soft shell, which is separated by sifting. in water and leave it in front of chickens,2without supervision, in contrast to the following halachah. lest it become chametz. However, we can boil bran for them,3As mentioned in Halachah 3, if grain products are placed directly in boiling water, they will never become chametz. and then place it before them. Nevertheless, the majority of people have already adopted the custom of not boiling [grain products], lest the water not be boiled thoroughly.4as explained in the above halachah and in the Shulchan Aruch and commentaries (Orach Chayim 454:3).

הלכה יח
וּמֻתָּר לָלוּשׁ לְתַרְנְגוֹלִין מֻרְסָן אוֹ קֶמַח וּמַאֲכִילָן מִיָּד אוֹ נוֹתֵן לִפְנֵיהֶן וְהוּא עוֹמֵד עֲלֵיהֶן עַד שֶׁלֹּא יַשְׁהֶה לִפְנֵיהֶן כְּדֵי הִלּוּךְ מִיל. וְכָל זְמַן שֶׁהֵן מְנַקְּרִין בּוֹ אוֹ שֶׁהוּא מְהַפֵּךְ בְּיָדוֹ אֵינוֹ מַחֲמִיץ. וּכְשֶׁיִּפְסְקוּ מִלֶּאֱכל יִשְׁטֹף הַכְּלִי בְּמַיִם וְיִשְׁפֹּךְ בִּמְקוֹם מִדְרוֹן:
כסף משנה
18.
It is permitted to prepare bran or flour for chickens in water1Rabbenu Manoach and the Meiri state that the Rambam's statements are based on the Tosefta. However, no law of this nature is found in our text of the Tosefta.
Perhaps this lack of a clear source is the reason the Rambam's opinion is not accepted by other halachic authorities. The Shulchan Aruch (Orach Chayim 465:1) forbids placing bran in water under any circumstances. The Ramah cautions against placing any grain products in a place where there is a residue of moisture.
if they are fed2and consume the food immediately, or if one places [the feed] before them and stands over them to ensure that the food will not stand3without any activity, as the Rambam continues more than the time it takes a person to walk a mil.4or 24 minutes, as explained in Halachah 13.
As long as they peck at it or one turns it over by hand,5for, like dough (see Halachah 13), as long as it is agitated it will not become leavened. Once they finish eating, one should wash out the utensil in water and pour it out in a place which slopes downward.6as in Halachah 16. This halachah also applies only after chametz has become forbidden. Even the authorities who follow a more stringent view than the Rambam allow leniency before the prohibitions against possessing chametz take effect.

הלכה יט
לֹא תִּשְׁרֶה אִשָּׁה מֻרְסָן שֶׁתּוֹלִיךְ בְּיָדָהּ לַמֶּרְחָץ. אֲבָל שָׁפָה עַל בְּשָׂרָהּ יָבֵשׁ. וְלֹא יִלְעֹס אָדָם חִטִּין וְיִתֵּן עַל מַכָּתוֹ מִפְּנֵי שֶׁהֵן מַחֲמִיצוֹת. אֵין נוֹתְנִין אֶת הַקֶּמַח לְתוֹךְ הַחֲרֹסֶת וְאִם נָתַן יִשָּׁפֵךְ מִיָּד מִפְּנֵי שֶׁהוּא מְמַהֵר לְהַחֲמִיץ. וְאֵין נוֹתְנִין אֶת הַקֶּמַח לְתוֹךְ הַחַרְדָּל וְאִם נָתַן יֹאכַל מִיָּד:
כסף משנה
19.
A woman should not soak bran which she intends to take to the bathhouse in water [beforehand].1The application of moist bran to skin renews the skin's natural moisture. Bran contains high quantities of Vitamin E and other natural cosmetics. However, she may rub dry bran on her skin.2even though her skin is moist with sweat, without fear of it becoming chametz (Rashi, Pesachim 39b). The Shulchan Aruch (Orach Chayim 465:2) forbids the practice entirely. A person should not chew wheat3for the spittle can cause the wheat to become leavened. and then place it on his wound,4as a poultice for it will become chametz.5Rabbenu Manoach notes that the Rambam writes (Hilchot Yesodai HaTorah 5:8) that, when there is danger to life or limb, it is permissible to use all substances as remedies, even if it is forbidden to benefit from them. That halachah specifically states that a sick person may be given chametz to eat as a remedy.
Furthermore, that halachah explains that if the sick person does not benefit from the forbidden substance in the normal manner, it may be used as a remedy even if there is no danger to life or limb. The Rambam gives the example of including chametz in a compress.
On that basis, Rabbenu Manoach questions why wheat cannot be used as a poultice as stated in our halachah. However, he resolves the issue by explaining that, in our case, the wheat would become chametz before it was applied to the wound.
The Shulchan Aruch HaRav 466:5 (and the Mishnah Berurah) emphasize that it is permitted to use grain as a remedy for a wound only if there is a question of danger to life or limb. Furthermore, this leniency is qualified as follows:
a) it must be an established medical fact that the remedy works;
b) effort must be made to reduce the chance of the grain becoming leavened to the greatest extent possible (e.g., preparing grain by boiling it in fruit juice which does not become leavened).

We should not place flour into charoset.6In his commentary on the Mishnah (Pesachim 10:3), the Rambam describes charoset as a mixture of dates, figs, spices, and vinegar. If one did so, he should burn it7The popular texts of the Mishneh Torah use the word ישפך - "pour it out." However, most of the original manuscripts state ישרף as in our text. This version implies that it is feared that the flour has already leavened and, hence, must be burnt. immediately,8as chametz because it will cause [the flour] to become leavened very fast.9In his commentary on the Mishnah (Pesachim 2:8), the Rambam explains that the vinegar in the charoset causes the flour to become leavened fast. We should not place flour in mustard.10The Ramah (Orach Chayim 464:1) states that Ashkenazic custom forbids the use of mustard on Pesach entirely, placing it in the category of kitniyot. If one did so, he should eat it immediately.11In contrast to other dips, the sharpness of mustard prevents the flour from leavening (Pri Chadash).

הלכה כ
מֻתָּר לִתֵּן הַתַּבְלִין וְהַשֻּׁמְשְׁמִין וְהָקֶצַּח וְכַיּוֹצֵא בָּהֶן לְתוֹךְ הַבָּצֵק. וְכֵן מֻתָּר לָלוּשׁ הָעִסָּה בְּמַיִם וְשֶׁמֶן אוֹ דְּבַשׁ וְחָלָב אוֹ לְקַטֵּף בָּהֶן. וּבַיּוֹם הָרִאשׁוֹן אָסוּר לָלוּשׁ וּלְקַטֵּף אֶלָּא בְּמַיִם בִּלְבַד. לֹא מִשּׁוּם חָמֵץ אֶלָּא כְּדֵי שֶׁיִּהְיֶה (דברים טז ג) "לֶחֶם עֹנִי". וּבַיּוֹם הָרִאשׁוֹן בִּלְבַד הוּא שֶׁצָּרִיךְ לִהְיוֹת זִכְרוֹן לֶחֶם עֹנִי:
כסף משנה
20.
It is permissible to place spices,1Nevertheless, the Shulchan Aruch (Orach Chayim 455:6) advises against placing spices in dough. The Ramah forbids matzah that was kneaded with pepper, maintaining that its sharpness causes the dough to become leavened. sesame seeds, poppy seeds,2The Shulchan Aruch HaRav explains that even the opinions which advise against using spices in matzah permit these substances to be used. They are not sharp and will not speed up the leavening process. and the like3Salt is not included in this category. The Shulchan Aruch (455:5) explicitly advises against placing salt into dough, and the Ramah considers matzah baked with salt as chametz. into dough.4for this mixture will not cause the dough to become chametz. In describing the meal offerings which cannot become leavened (Hilchot Ma'aseh HaKorbanot 12:17), the Rambam also states that they may be seasoned in a similar manner.
The Tosefta (Pesachim 2:13) and the Jerusalem Talmud (Pesachim 2:4) go further and state that such matzah may even be used at the Seder. Though some halachic authorities accept this opinion, the later authorities counsel against using such matzah on that occasion.
Similarly, it is permissible to knead the dough with water and oil, honey or milk, or to baste with them.5This statement has raised controversy. In Halachah 2, when the Rambam described the use of מי פירות, he explained that they will not cause grain products to become leavened when used alone. However, if they are mixed with water, they can cause the grain products to become leavened. Indeed, the commentaries relate that the mixture of these liquids with water speeds up the leavening process.
Therefore, the Ra'avad and other authorities question the leniency granted by the Rambam. In practice, the Shulchan Aruch (Orach Chayim 462:2) advises against, but does not forbid, mixing these liquids with water. The Ramah (and accordingly, Ashkenazic custom) prohibits such a mixture entirely.
It must be noted that the Maggid Mishneh's text of the Mishneh Torah substitutes the word יין (wine) for מים (water). According to such a rendition, there is no difficulty.

On the first day,6more particularly, for the matzah used to fulfill the commandment of eating matzah on Pesach night; it is forbidden to knead or baste7even though basting the dough with other substances will not change its taste appreciably, the Rambam forbids this. See Or Sameach. [the matzot] with any other substance besides water;8Note the commentary on Halachah 6:5. not because of the prohibition against chametz,9for, as above, the dough will not necessarily become chametz, but rather so [the matzah] will be "poor man's bread."10Deuteronomy 16:3 states "For seven days eat matzah, poor man's bread." In contrast, dough mixed with these liquids is considered matzah ashirah, "rich matzah." It is only on the first day that the "poor man's bread" must be commemorated.11to recall the "poor man's bread" eaten by our ancestors when they were slaves in Egypt.

הלכה כא
כָּל כְּלִי חֶרֶס שֶׁנִּשְׁתַּמֵּשׁ בָּהֶן חָמֵץ בְּצוֹנֵן מֻתָּר לְהִשְׁתַּמֵּשׁ בָּהֶן מַצָּה בְּצוֹנֵן. חוּץ מִכְּלִי שֶׁמַּנִּיחִין בּוֹ אֶת הַשְּׂאוֹר וּכְלִי שֶׁמַּנִּיחִין בּוֹ חֲרֹסֶת מִפְּנֵי שֶׁחִמּוּצוֹ קָשֶׁה. וְכֵן עֲרֵבוֹת שֶׁלָּשִׁין בָּהֶן הֶחָמֵץ וּמַנִּיחִין אוֹתוֹ שָׁם עַד שֶׁיַּחְמִיץ הֲרֵי הֵן כְּבֵית שְׂאוֹר וְאֵין מִשְׁתַּמְּשִׁין בָּהֶן בְּפֶסַח:
כסף משנה
21.
All earthenware vessels1In this and the following five halachot, the Rambam discusses how dishes and cooking utensils that were used for chametz during the entire year may be prepared for Passover use. It must be emphasized that in many communities, it is customary not to consider these options and to use separate sets of pots, dishes, and cutlery for the holiday. that were used for chametz while cold2Utensils absorb substances only when used together with both heat and liquid. Thus, in this instance, there is no fear that chametz is absorbed. Nevertheless, the utensil may3only be used for matzah while cold,4lest its use cause people to err and permit use of earthenware vessels that were used for chametz while hot (Maggid Mishneh). This safeguard was only instituted for earthenware vessels, since the chametz absorbed in substances of metal or wood may be purged through הגעלה.
The Shulchan Aruch (Orach Chayim 451:22) does not recognize this prohibition at all and allows such utensils to be used for matzah even when hot. However, this is merely from an abstract halachic perspective. In practice, that text continues to explain, Jews are accustomed not to use any earthenware utensils or dishes that had been previously used for chametz on Pesach. This custom was already accepted in the days of Rav Yitzchak Alfasi and Rabbenu Asher.
except for the utensils5Leavening agents were placed directly in these utensils. Accordingly, even if they were made of other substances besides clay, more severe laws than usual apply regarding purging them from the chametz they absorbed. (See Magen Avraham 451:42.) in which yeast and charoset6This does not refer to the charoset used at the Seder, but to a similar mixture which was used throughout the entire year. The latter would frequently contain flour. were placed, for their leavening effect is powerful.7Yeast is a powerful leavening agent. Similarly, the vinegar in the charoset will cause leavening. Even though the utensil was cleaned thoroughly of these substances, we regard that some was absorbed in the utensil's walls and will have an effect on food placed within it on Pesach. Similarly, a kneading trough in which chametz is kneaded and left to become leavened is considered as a place where yeast is soaked, and we do not use it on Pesach.8lest the leavening agents that are absorbed cause the Matzah to become chametz.

הלכה כב
בִּיב שֶׁל חֶרֶס שֶׁאוֹפִין עָלָיו חַלּוֹת חָמֵץ כָּל הַשָּׁנָה כֻּלָּהּ אֵין אוֹפִין עָלָיו מַצָּה בְּפֶסַח. וְאִם מִלְּאוֹ גֶּחָלִים וְהִסִּיק מָקוֹם שֶׁהָיָה מְבַשֵּׁל בּוֹ הֶחָמֵץ מֻתָּר לְבַשֵּׁל עָלָיו מַצָּה:
כסף משנה
22.
An earthenware roasting pan on which loaves of chametz are baked during the entire year should not be used to bake matzah on Pesach.1The prohibition is obvious. It appears that this statement was included only as an introduction to the following halachah, which describes how such a utensil may be prepared for Pesach use. If it was filled with coals and kindled on the place2This practice, referred to as ליבון, burns up any chametz that may have been absorbed in the pan. where chametz was cooked, matzah it is permitted to be cooked on it.

הלכה כג
כְּלֵי מַתָּכוֹת וּכְלֵי אֲבָנִים שֶׁנִּשְׁתַּמֵּשׁ בָּהֶן חָמֵץ בְּרוֹתְחִין בִּכְלִי רִאשׁוֹן כְּגוֹן קְדֵרוֹת וְאִלְפָּסִין. נוֹתֵן אוֹתָן לְתוֹךְ כְּלִי גָּדוֹל שֶׁל מַיִם וּמְמַלֵּא עֲלֵיהֶן מַיִם וּמַרְתִּיחָן בְּתוֹכוֹ עַד שֶׁיִּפְלְטוּ וְאַחַר כָּךְ שׁוֹטֵף אוֹתָן בְּצוֹנֵן וּמִשְׁתַּמֵּשׁ בָּהֶן בְּמַצָּה. וְכֵן הַסַּכִּינִין מַרְתִּיחַ אֶת הַלַּהַב וְאֶת הַנִּצָּב בִּכְלִי רִאשׁוֹן וְאַחַר כָּךְ מִשְׁתַּמֵּשׁ בָּהֶן בְּמַצָּה:
כסף משנה
23.
Metal and stone utensils1In Hilchot Ma'acholot Asurot 17:3 and in his commentary on the Mishnah (Avodah Zarah 7:12), the Rambam equates glass utensils with those made of these substances. in which chametz was boiled in water as a כלי ראשון2The term כלי ראשון is a fundamental concept in the laws of kashrut and the laws of Shabbat. It refers to a pot or cooking vessel that was directly exposed to the heat of an oven or range. Such a pot is still considered as a כלי ראשון even after it has been removed from the cooking surface. - e.g., pots and stew pots3The Ramah (Orach Chayim 451:5) requires that the surface of the pot be smooth and free of nicks or cracks for this manner of purging to be effective. - should be placed inside a large utensil.4The process described below can be carried out only before chametz becomes forbidden. Once that prohibition takes effect, even the slightest amount of chametz can cause a larger mixture to be prohibited. (See Halachah 1:5.) Hence, were the process carried out at that time, the residue of chametz absorbed in the walls of the utensils would cause all the water to be considered as mixed with chametz. They should be covered with water, and the water should be boiled5The commentaries stress how the water must be bubbling because of the heat. with them inside6This process is referred to as הגעלה (purging) and is also used to prepare utensils that had been used for non-kosher food for kosher use. Thus, a similar description of this process is found in Hilchot Ma'achalot Asurot 17:4.
The basic principle governing the kashering of utensils is כבולעו כך פולטו - "In the same manner as a [forbidden substance] is absorbed [by a utensil], so, too, is it released." Thus, since these utensils were used in hot water, the process of boiling is employed to cause them to release any chametz they might have absorbed.
until they release [what they absorbed].7This phrase is taken from the halachot of Rav Yitzchak Alfasi. However, it is omitted in some of the Yemenite manuscripts of the Mishneh Torah. In practice, there is also debate about this issue. In his responsum, the Rashbah explains Rav Yitzchak Alfasi's view, stating that a person should leave the utensil submerged until he feels that all the absorbed chametz has been released. However, the Tur (Yoreh De'ah 121) and the Pri Chadash do not require waiting any substantial amount of time. Their view is accepted by the later authorities. (See Shulchan Aruch HaRav, Orach Chayim 452:4.) Afterwards, they should be washed off with cold water,8in order to cleanse them of any forbidden matter that might remain on their surface (Rabbenu Manoach). The source for this requirement is the description (Zevachim 97a) of the way the priests would purge the Temple pots used to cook the sin offerings after the previous day's service. Though some authorities do not require this stage, the Shulchan Aruch HaRav (452:5) states that it is customary to follow this practice. and [then] one may use them for matzah.9Hilchot Ma'achalot Asurot 17:7 states: "A person who acquires a knife from a gentile must burn it out in fire." A similar decision is rendered by the Shulchan Aruch (Yoreh De'ah 121:7). Nevertheless, the authorities suggest that chametz may be purged from knives by boiling. However, they do not permit this leniency in the following instances:
a) when the knives are rusty;
b) when they have serrated edges;
c) when the handle is separate from the blade and enclosed around it, allowing for the possibility for residue to collect between them.
In the latter instance, even ליבון (exposing the knife to open fire) is insufficient. Since most knives today are made in this manner, they should not be kashered for Pesach or for ordinary use after having been used with prohibited foods. Both the Mishnah Berurah and the Shulchan Aruch HaRav state that purchasing new knives for Pesach is the most desirable manner of fulfilling the mitzvah.

Similarly, [with regard to] knives, the blade and the handle should be boiled in a כלי ראשון.10as described above. Afterwards, one may use them for matzah.

הלכה כד
כְּלֵי מַתָּכוֹת וַאֲבָנִים וּכְלֵי עֵצִים שֶׁנִּשְׁתַּמֵּשׁ בָּהֶן חָמֵץ בִּכְלִי שֵׁנִי כְּגוֹן קְעָרוֹת וְכוֹסוֹת נוֹתֵן אוֹתָן לְתוֹךְ כְּלִי גָּדוֹל וְנוֹתֵן עֲלֵיהֶן מַיִם רוֹתְחִין וּמַנִּיחָן בְּתוֹכוֹ עַד שֶׁיִּפְלוֹטוּ וְאַחַר כָּךְ שׁוֹטְפָן וּמִשְׁתַּמֵּשׁ בָּהֶן בְּמַצָּה:
כסף משנה
24.
Utensils of metal, stone, and wood which were used for chametz as a כלי שני1a utensil into which one pours water that had been cooked over a fire. - e.g., bowls or cups2can also be purged of chametz following the principle כבולעו כך פולטו - "In the same manner as a [forbidden substance] is absorbed [by a utensil], so, too, is it released." Thus, since these utensils absorbed chametz in a שני כלי, in order for them to release the chametz they absorbed, they - should be placed in a large utensil, and boiling water poured over them.3from a utensil that was heated on the fire. The Ramah (Orach Chayim 451:6) states that, at present, it is customary to boil all utensils on the fire itself (i.e., in a כלי ראשון), even though they were generally used as a כלי שני. They should be left in [the large utensil] until they release [the chametz they absorbed].4See the explanation of the similar phrase in the previous halachah. Afterwards, they should be washed off.5as explained in the previous halachah. [Then,] they may be used for matzah.

הלכה כה
כָּל כְּלִי חֶרֶשׂ שֶׁנִּשְׁתַּמֵּשׁ בָּהֶן חָמֵץ בְּחַמִּין בֵּין כְּלִי רִאשׁוֹן כְּגוֹן קְדֵרוֹת. בֵּין כְּלִי שֵׁנִי כְּגוֹן קְעָרוֹת. בֵּין שֶׁהָיוּ מְשׁוּחִין וְשׁוּעִין בַּאֲבַר שֶׁעוֹשִׂין אוֹתָן כְּעֵין זְכוּכִית. בֵּין שֶׁהָיוּ חֶרֶס כְּמַה שֶּׁהֵן. אֵין מִשְׁתַּמְּשִׁין בָּהֶן בְּמַצָּה אֶלָּא מַנִּיחָן לְאַחַר הַפֶּסַח וּמְבַשֵּׁל בָּהֶן:
כסף משנה
25.
All earthenware utensils that were used for chametz in hot water,1In contrast to utensils made of other substances, the process of הגעלה cannot remove the forbidden matter absorbed in the walls of an earthenware vessel. Instead of all the absorbed matter being purged at once, it is released a small amount at a time, and there will always be a certain quantity of the previous substance contained in its walls.
Pesachim 30b explains that this concept is derived from the Torah itself. Leviticus 6:21 states that any pot in which meat from a sin offering has been cooked must be broken. A sin offering can only be eaten for one day. Once that time has passed, the taste of the meat absorbed in the pot is considered as נותר (sacrificial meat which has been kept past its required time), and thus forbidden. Hence, the pot itself must be destroyed.
whether as a2 כלי ראשון - for example, pots3or as a כלי שני - or as a
כלי שני - for example, bowls4whether they were glazed and coated with lead so that they became like glass -- i.e., china. Based on these principles, the authorities have stated that china can never be kashered. However, they have suggested certain leniencies when the china is very expensive. - whether they were glazed and coated with lead so that they became like glass, or they were of simple earthenware:5As mentioned in Halachah 22, the Sages also forbade the use of ןוביל (exposing the utensil to fire), to remove chametz absorbed in most earthenware vessels, lest a person hesitate to expose them to the required heat out of fear that they would break. Thus, there is no way to prepare these utensils for Pesach use. Therefore, we do not use them for matzah.6There would be no halachic difficulty against using these dishes on Pesach for cold foods. Nevertheless, our Sages forbade their use entirely, lest a person err and use them for hot substances as well. Rather, we put them aside until after Pesach,7Though the taste of chametz is absorbed in the walls of these utensils, keeping them does not cause a person to violate the prohibition against possessing chametz on Pesach. Nevertheless, at present, when it is customary to sell chametz to gentiles, the Rabbis in charge of the sale usually sell this chametz as well. and then we may cook with them.8This line was added to negate the opinion of Rav (Pesachim 30a), who maintains that each Pesach, a person was required to destroy any earthenware vessels he possessed which were used for chametz while hot.

הלכה כו
כְּלִי רִאשׁוֹן שֶׁרָצָה לְהַרְתִּיחוֹ וְלֹא מָצָא כְּלִי גָּדוֹל מִמֶּנּוּ כְּדֵי לְהַרְתִּיחוֹ בְּתוֹכוֹ הֲרֵי זֶה מַקִּיף לוֹ שָׂפָה שֶׁל טִיט עַל שְׂפָתוֹ מִבַּחוּץ וּמְמַלְּאֵהוּ מַיִם עַד שֶׁיִּגְבְּרוּ הַמַּיִם עַל שְׂפָתוֹ וּמַרְתִּיחַ הַמַּיִם בְּתוֹכוֹ וְדַיּוֹ וְאַחַר כָּךְ שׁוֹטֵף אוֹתוֹ וּמִשְׁתַּמֵּשׁ בּוֹ בְּמַצָּה:
כסף משנה
26.
[A person possesses a utensil which is] a כלי ראשון and desires to boil it [in order to prepare it for Passover use],1and hence must be kashered by boiling water inside of it, as explained in Halachah 23. however, he cannot find a larger utensil into which [to place it] to boil it:2Thus, were he to boil water in the utensil itself, its entire top edge would not be exposed to the boiling water. Behold, he may place a border of clay around its [top] edge from the outside and fill it3the utensil with water until the water overflows its edge.4but is delayed in pouring out by the clay border. [Then,] he may boil the water in it, and this is sufficient.5for the entire utensil will have been exposed to the boiling water. The Shulchan Aruch (Orach Chayim 452:6) offers an alternative suggestion. After boiling the water thoroughly, placing a very hot stone into the water will cause the water to flow over the edges of the utensil on all sides. Thus, the entire utensil will be exposed to the boiling water. Afterwards, he washes it off6with cold water, as explained in Halachah 23. and may use it for matzah.

זמנים הלכות חמץ ומצה פרק ה
Zemanim Hametz and Matza Chapter 5