Hafrashat challah from holy dough
Question
Friday afternoon, I was making challah and ran out of canola oil, so I supplemented with my shemitah olive oil. I finished making the batch, which was large enough to be obligated in separating challah, when I suddenly realized that there might be a problem: If the entire batch of dough is now holy, would it be a problem to burn the challah that I set aside, like I usually do?
Answer
Short answer
While there is a conflict between the prohibition to eat challah and hefsed, there is a way of separating the challah without directly spoiling the shemitah produce:
Double-bag the dough you set aside (just like other shemitah leftovers) and in this way you will not directly spoil the dough.
Expanded answer
On the one hand, we must separate challah from the dough and the dough is considered terumah. In the times when ritual purity was observed, we would give this dough (or roll) to a kohen, who would eat it in a state of purity.
Now, however, since kohanim are impure, no one can eat this dough and it is generally burned.
However, as you noted correctly, this poses a conflict with the prohibition of directly spoiling shemitah produce, hefsed.
Even though you generally burn the dough, now you should double bag it before disposal, so that you do not spoil it directly.
This case resembles another conflict between two halachic obligations: burning chametz on erev Pesach for holy shemitah produce. In this case, if you recall, we noted that the holy chametz may only be burned starting from the time it is prohibited to eat chametz (the 5th halachic hour), because at this time it must be burned and cannot be eaten in any event. Before this time, burning shemitah chametz would be considered hefsed.
This law is actually derived from equating the laws governing terumah to those of shemitah produce, both of which may not be destroyed directly.
In the case of terumah chametz, however, the Gemara (Pesachim) explicitly states that it is burned erev Pesach. When challah is concerned, however, it is also permissible to set the dough aside an allow it to spoil on its own, this is the best mode of action.