As always, the EOC treats things we cannot fully understand as inspired knowledge that remain a mystery and Eucharist is certainly one of those mysteries.
Not much has been written about it, but even St. Paul hints that it might be the real thing. After Paul, and quite some time after the Gospels were written, Irenaeus was hinting at the nature of "change" in the Eucharist as earl at 106 AD
But the whole idea of eating human flesh and drnking wine was abhorrant to the Jews as it is to us. Yet the Christian world sees the whole issue differentlyw when it comes to Eucharist.
The custom is certainly not in the Jewish tradition, but the Gospels leave no doubt that (1) we are to celbrate the Supper in memory of Him and that the bread "is" His body and the wine "is" His blood. Whether that constitutes cannibalism, as some have accused Christians of, or not is altogether unclear, but I would like to err on the divine side and say that the spirit of His gifts is present (and I am blaspheming here), until I am shown any different.
Actually we don't. There are differences. It is a Roman Catholic doctrine, formulated at a council which we don't recognize.
""Transubstantiation" is a term coined by the scholastic theological tradition of the Roman Catholic Church. Owing to the contacts with the West, Orthodoxy sometimes picked up on such terminology and used it to express the Orthodox understanding of what the Holy Trinity does during the DIvine LIturgy to change the bread and wine into the Body and Blood of our Lord, God and Saviour, Jesus Christ. This was especially true of the Kyivan Baroque period where St Peter Mohyla, Metropolitan of Kyiv, tended to use borrowed western phraseology in his Catechism and elsewhere. This is why Metropolitan Ilarion Ohienko used the term "Transubstantiation." Ohienko was a great scholar of Orthodox history and antiquity and was well acquainted with the theological terminology of the Baroque period.
Transubstantiation is weak terminology because of its rationalist underpinnings. Transustantiation says that the "substance" of the bread and wine are changed, but that the "accidents" i.e. the physical appearance of the bread and wine remain. There is already a problem here with separating, in theoria, the substance and the accidents, or, to put it another way, to began talking about the two as separate entities. There is a real pit-fall in that when we talk about the accidents, the physical qualities of bread that remain after the Eucharistic Change occurs, there is the seemingly unavoidable suggestion made that the bread itself remains. How else can we identify the bread if not through its qualities? And if the qualities remain unchanged, then the substance of bread must somehow also remain -- now we are really in deep trouble and have fallen into the heresy of "consubstantiation" the idea that the Body and Blood of Christ "co-exist" with the bread and the wine. Martin Luther believed in consubstantiation as a possible explanation, but he didn't condemn transubstantiation either which is why either position is acceptable in Lutheranism today. I think that there is a sense in which transubstantiation leads one into consubstantiation which is why "transmutation" is a better term, as Fr. Brygidyr, speaking from within the best traditions of Orthodoxy, states.
Transmutation doesn't get us into the unnecessary and rationalistic positions of neatly defined categories etc. such as accidents and substance. It simply posits that the reality of the bread and wine is changed after the last "Amen" is said following the Epiclesis and the Eucharistic Canon. It doesn't get into the "how" of the change. It is, unfortunately, very typical of the Western scholastic tradition to want to know "how" such as, for example, "how does the Holy Spirit proceed from the Father and remain distinct from the Son who is Only-Begotten?" The "Filioque" was therefore a rationalistic - and unscriptural - way of responding to this rationalistic question. This has led to all kinds of problems in the Roman Catholic church which it has yet to overcome, even with the Second Vatican Council (some would say "especially with").
Dr. Alexander Roman alex@unicorne.org