Genesis 43:32
And they set on for him by himself, and for them by themselves, and for the Egyptians, which did eat with him, by themselves: because the Egyptians might not eat bread with the Hebrews; for that is an abomination unto the Egyptians. And they set on for him by himself, and for them by themselves, and for the Egyptians, which did eat with him, by themselves: because the Egyptians might not eat bread with the Hebrews; for that is an abomination unto the Egyptians.
The Egyptians regarded eating bread with Hebrews, as people of another nation, as an abomination. At Joseph's feast this required three separate settings, one for Joseph by himself, one for his brothers by themselves, and one for the Egyptians who ate with him by themselves. Joseph also dined apart from the others because of his high rank. This separation reflected the strict caste distinctions observed among the Egyptians.
At their own table the brothers were arranged in order of age from the eldest by birthright down to the youngest, as was customary when ages were known, which astonished them because they thought he could have no knowledge of their ages. The same abomination explains why Potiphar put all that he owned into Joseph's hand but kept the bread he ate in his own charge, since Egyptians counted it an abomination for a Hebrew to prepare food for an Egyptian.