The Mishna (עבודה זרה לה) writes that it is forbidden for a Jew to eat Pat Akum, bread baked by a non-Jew baker. Rather one must only buy Pat Yisrael, bread baked by a Jewish baker. The main reason written in the Gemara is that bread is a very important part of daily life, and if one consistently partakes of the bread of a non-Jew and mingles with non-Jewish people it may start a relationship which can easily lead to intermarriage. Pat akum is one of many things that chazal made assur in order to keep Jews and non-Jews from mingling too much.
The Rama writes (יו”ד סי’ קיב סעיף א) even though the reason for the prohibition of pat akum is to avoid intermarriage, it is still forbidden to eat bread baked by a non-Jew when there is no possibility of intermarriage, such as a non-Jew who does not have daughters. The Shach (שם ס”ק ד) explains that even if this person doesn’t have a daughter to marry off, he has friends who do, and once you start befriending one you will quickly get to know others.
The Gemara on the previously quoted Mishna writes that Rebbi was visiting his students and he saw that they did not have bread to eat. Rebbi asked them “Do you not have bakers in this town?”. There are two opinions about what Rebbi meant to say; either Rebbi was merely asking where were the Jewish bakers. Alternatively, Rebbi was asking that if there was no bread available from a Jewish baker, why didn’t they buy bread from a non-Jewish baker. The Gemara says that even if Rebbi was saying that they were permitted to buy pat akum this would only be permitted under certain conditions. Rabbi Chelbo says it is permitted when there is no bread available from Jewish bakers, and Rabbi Yochanan says it is permitted when one is traveling.
There are three opinions amongst the rishonim regarding when pat akum is permitted. The Ran (מובא בב”י סימן קיב) writes that Rabbi Chelbo and Rabbi Yochanan agree with each other, and therefore one may eat pat akum when there is no bread available from a Jew, or if they are traveling. The Rambam (מאכלות אסורות פרק יז הל’ יב) writes that one needs both conditions to eat pat akum. One must be out of the city and there also must be no pat yisrael available. Tosfot (עבודה זרה לה ד”ה מכלל) writes that this prohibition was never accepted by the public and therefore pat akum is always permitted.
It is important to note that there are two types of pat akum. Pat palter is bread of a commercial baker. This is bread which was baked to sell and not to be eaten privately. Pat Baal Habayit is bread that a non-Jew baked with the intention of keeping it for himself, not to sell. We will discuss the specific halachot of each category later.
The Shulchan Aruch writes that one may buy pat palter if there is no pat yisrael available. (The Shulchan Aruch is seemingly quoting the Ran, however he does not mention what the halacha would be if one was traveling, where the Ran permits one to buy pat palter.) The Rama holds like Tosfot and writes that pat palter is always permitted, even if pat yisrael is readily available. The Shach (שם ס”ק יב) writes that it is proper to be stringent like the Shulchan Aruch, and especially during the Ten Days of Repentance between Rosh Hashanah and Yom Kippur one should not eat pat palter. The Chelkat Binyamin (סי’ קיב סעיף ב) writes that even the Shach would permit eating pat palter when one is traveling, whether pat yisrael is available or not.
Rav Moshe Feinstein (אגרות משה יו”ד ח”ב סימן לג) writes that we rule like the Rama, and pat palter is always permitted. However, many poskim are stringent like the Shach (פר”ח ס”ק ט, ערוך השלחן סעיף ט). The Mishna Berura (סי’ רמב ס”ק ו) writes that it is proper to be stringent like the Shach, to refrain from eating pat palter during the Ten Days of Repentance, as well as on Shabbat.
The Shulchan Aruch writes that even though pat palter is not permitted when pat yisrael is available, there are several situations when one may eat pat palter. These circumstances would permit pat palter year round even according to the Shach and those that are careful not to buy pat palter during the Ten Days of Repentance or for Shabbat. The first case that Shulchan Aruch brings (שם סעיף ג) is when pat yisrael is not easily available. The Chelkat Binyamin (סימן קיב ס”ק יט) explains that this means there is no bread available from a Jewish baker, and even though there may be bread from a private person available you are not required to go get from the private person to avoid buying pat palter. The Darkei Teshuva (ס”ק כט) writes that even when pat yisrael is available, if there is not enough for all the Jews of the city, it is considered as if there is no pat yisrael available and one may buy pat palter. The Darkei Teshuva (ס”ק כו) adds that once we permit purchasing pat palter, one may buy and eat as much as they wish, we do not limit the permissibility to the minimum amount necessary.
Another instance when pat palter is permitted (שו”ע יו”ד סי’ קיב סעיף ה) is when the pat palter is of better quality than the pat yisrael, or is a different kind of product which is unavailable in pat yisrael form. Since the pat palter is better or a different kind it is considered as if that bread is unavailable in pat yisrael.
The following is a short general explanation of what is included in “pat” and would have the halachot of pat akum. Only foods made from the five types of grain are included. The five grains are wheat, barley, spelt, oats, and rye. Foods made from corn flour or rice flour are not included in pat. If the food is a mixture of flours that are included in pat and flours that are not, the food has the status of the flour which is the majority. If the flour is in the recipe as a thickener and not for taste (such as in twizzlers) then the flour is secondary to the food, and the food does not have the rules of pat akum. Pat includes anything which is pat haba bekisnin, meaning a snack which is of the type that can also be eaten as a meal. Such a snack (such as a croissant) is mezonot, but if enough would be eaten to be considered a meal, one would be required to wash and make a hamotzi on the food. According to the Shach (יו”ד סי’ קיב ש”ק יח) food made from a batter (as opposed to a dough) is not included in pat akum. The Torat Chatat brought in the Shach explains that one does not make a birkat hamazon on foods made from batter. The Chelkat Binyamin (סי’ קיב ס”ק סד) writes that most poskim disagree with the Shach, and baked products made from batter would be included in pat akum. Deep fried foods, such as doughnuts, are not included in pat akum, unless it was baked after the frying, because no matter how many doughnuts one eats they would not be required to recite birkat hamazon.
