There are foods that may not be eaten even when all their ingredients are kosher and the cooking is supervised: foods that were cooked or baked by a non-Jew.
About 2,000 years ago, in the time of the Tannaim, the Sages (Chachamim) established this rule. The aim was to prevent intermarriage: not being able to share a meal with someone keeps a distance from that person.
The rule has two parts: Pat Israel, for baked bread, and Bishul Israel, for all other cooked food.
Pat Israel is bread made by a Jew. But not everything baked counts as bread. According to Halacha, "bread" is only what is made from the five grains, wheat, barley, rye, spelt and oats, and baked.
When the decree was made, many communities had no Jewish bakers and relied on the local baker. So Pat Palter was permitted: since the aim was to avoid social closeness, mass production for sale does not involve that personal contact.
Halachic authorities disagree about how far this goes:
This does not mean bread can be bought at any bakery. Pat Palter only settles who baked the bread, not what is in it. At an unsupervised bakery there is no way to know which ingredients were used, and that is a separate problem. The leniency applies only in a supervised place, where the ingredients are checked.
Bishul refers to cooked food. Unlike bread, there is no allowance here for commercial production: it makes no difference whether the product was made in a factory or at home. For a food to fall under these laws it must meet both conditions at once:
Require Bishul Israel: meat, rice, baked potatoes, beans, crepes.
Do not require it: apples, cucumbers, onions, almonds, all kinds of breakfast cereals, potato chips. Coffee does not either: although it is not drunk raw and is served at important tables, its main ingredient is water, which is consumed raw.
The Jew does not have to do all the work. For Pat Israel it is enough to take part in the lighting: turning on the oven, or putting the dough in.
For Bishul, customs differ. Ashkenazim treat it the same as Pat Israel. Sephardim follow the opinion of the Beit Yosef: the Jew must put the food on the fire.
This summary is for general guidance only. For a practical answer about a specific case, please consult a Rav.
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