971. An Eiruv of Impermissible Food

Eiruvin 6:15

If a person made an eiruv with terumah about which there is a doubt as to whether or not it is ritually clean, the eiruv is not valid because the food is not fit to eat. The same is true if a person had two loaves of terumah bread, one of which was ritually clean and one of which was ritually unclean, and he didn’t know which was which. Even if he said, "Let the ritually-clean loaf serve as my eiruv," the eiruv is not valid because the meal is not fit to eat.

Eiruvin 6:16

If a person declared that a certain loaf of bread is not consecrated that day but it will be consecrated the next day, an eiruv made using that loaf is valid. This is because the loaf is not definitely consecrated at twilight, and is therefore fit to eat before Shabbos begins. However, if he said that it is consecrated that day and not the next, it may not be used for an eiruv because it is only fit to eat after Shabbos begins. Similarly, if one separated terumah with the condition that it not become terumah until nightfall, it may not be used for an eiruv. This is because it is still considered untithed throughout the twilight period and the food for an eiruv must be fit to eat before Shabbos begins.