Dear For,
The purpose of theology is not to replace faith with sure knowledge, but to show that it is not unreasonable to believe. The accidents, those aspects of the Eucharist that are not essential to it (the appearances, the weight, taste, natural effects), do not change. Only the very essence of the bread and wine changes. The change that takes place cannot be physically measured or seen. The Eucharist requires the same faith from us that it required of the disciples.
Fr. Vincent Serpa, O.P.