This is admittedly not a pleasant question to bring up, but it does go a long way in illustrating the graphic consequences of the dogma of transubstantiation. The Catechism of the Roman Catholic Church says that the wafer is Jesus "as long as the Eucharistic species subsist" (CCC # 1377). The duration usually given for this is fifteen minutes. But this dodge, as convenient it may seem, is not a satisfactory explanation.
How come the Eucharistic species cannot subsist for thirty minutes or an hour? Who gets to make a decisive ruling on this matter? What would this process of the deconversion of digested communion elements even be called?
The biblical view of communion is a remembrance of the work of Christ on the Cross at Calvary (1 Corinthians 11:23-25). We do not need to resort to philosophical speculation in order to avoid the logical absurdities of transubstantiation.