Ignatius identifies the Eucharist as the flesh of Jesus Christ that suffered for our sins (Smyrnaeans 7). Justin says Christians receive it ‘not as common bread and common drink’ but as the flesh and blood of the incarnate Jesus (First Apology 66). Irenaeus speaks of the bread, after the invocation, as no longer common bread but Eucharist, consisting of earthly and heavenly realities (Against Heresies 4.18). Cyril of Jerusalem tells communicants not to judge by taste alone but to receive the gifts as Christ’s Body and Blood (Catechetical Lecture 22).
The Fathers sometimes speak of signs, figures, and spiritual reception. Those terms belong to sacramental realism in their context; they do not turn the Eucharist into a bare recollection. The precise philosophical explanations came later, but the underlying confession did not begin in the Middle Ages.
Primary sources
Ignatius, Smyrnaeans 7: https://www.newadvent.org/fathers/0109.htm
Justin, First Apology 66: https://www.newadvent.org/fathers/0126.htm
Irenaeus, Against Heresies 4.18: https://www.newadvent.org/fathers/0103418.htm
Cyril, Catechetical Lecture 22: https://www.newadvent.org/fathers/310122.htm