A theoretical question: Someone was making a dough and in the process a large piece fell out from the mixture onto the floor. They had made exactly the right amount in order to take challah with a bracha. The part that fell onto the floor they now no longer want to use as part of the dough. Therefore the mixture is now missing a proper "shiur" (amount) in order to take challah with a bracha. Can a bracha still be made when challah is taken from the dough in such a case?
To begin with one could ask, when does the dough become chiyuv in general in taking off challah? Does it help in this case that the piece of dough is still around and can be put together with the entire mixture, then separate the challah with a bracha, even though the person will not use this piece and throw it away. Would it make a difference if the piece of dough that fell off was no longer around at all?