Eruvin 31 - Marginally valid foods
There are foods that are somewhat prohibited but that can still be used for a Shabbat eruv - communal food which permits them to carry in an alley. For example, if he bought fruit in the market and has a doubt if the tithes were properly separated, he can still use this for an eruv - since poor people can eat it, and he can make himself poor by renouncing all his possessions.
However, if the food is definitely not tithed, then it cannot be used for an eruv, because one is not allowed to tithe on Shabbat, and thus the food is not edible by anybody.
A similar list of of foods is found in many places in the Talmud, for example, it applies to the laws of a communal prayer after a meal: one who ate doubtfully tithed produce may be joined in this prayer, but one who ate definitely untithed produce cannot.
Art: George Walter Harris - Summer fruits
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