I understand that Lutherans believe in the real, physical presence of Christ in the Eucharist, but not in such a way that the species cease to be true bread and wine. So you are physically eating God, but you are also physically eating bread. (Similar to the hypostatic union of Christs two natures: Christ is fully human and fully divine. The bread is fully bread but also fully Christ).
I was wondering when the consecrated species cease to be divine and return to normal, natural, mundane matter. I heard somewhere a long time ago that Lutherans believe that the real presence only continues for duration of the liturgy and once the mass concludes the species return to being normal bread and wine; I have not been able to confirm this.
Perhaps the Lutheran view is similar to the Catholic view. That is, the sacramental union persists so long as the bread and wine are recognizable as bread and wine. Once they have gone moldy, turned to vinegar, evaporated or been digested, the body and blood are no longer present.