@KingaRoo, the belief in transubstantiation is from the earliest history of the church. The term that Christ uses in the Hebrew (so my scripture lecturer told me, I can't recall the actual word now) was like masticate; the literal translation is more like 'Whoever chews and consumes my flesh and drinks my blood will have life eternal.'
The early Roman state in fact used to prosecute the early Christian communities for Cannibalism (this is reported by Suetonius who is not exactly a reliable author, but even if he's the Daily Mail equivalent, it still shows a wide spread awareness of their belief that it was the actual, literal body and blood of Christ) - based on the fact that they were reported to be consuming flesh. It was also a part of what made Christ's command so shocking to the Jews of the day, because Cannibalism was strictly forbidden - it is an abomination (the most severe term the Torah uses to condemn).
There are other stories and midrashes that defend this belief as being part of the patristic history of the church, but I think i've said enough to defend that for now. The actual doctrine of transubstantiation was clarified in the 13th Century (I think? Someone else may know the precise council). The actual working of the belief of transubstantiation was clarified using Aristotelian metaphysics; i.e.: the understanding that things can be essentially what they are, but still have particular characteristics that are accidental and not essential to what they are. So the bread and the wine is transubstantiated; it's substance (in the Greek ousia) is changed into the Body and Blood of Christ; it retains the accidental features of bread, the taste, colour, etc., but has a new essence.
This is in parallel to the human experience of the Holy Spirit - that we retain the same accidental features of who we are, but we can have a new spirit that gives us life, so that we can give others life. We also, can be transformed, although our substance does not change it can be renewed by the gift of the Holy Spirit.
This is also the meaning of the term Sacrament - an external sign of an internal reality; so Baptism is an external sign of a new life that is being given, by the Church and by God, to a new Christian, to being the process of faith. Confession (and the priestly laying on of hands) is an external sign of the internal reality of God washing away our sins. The Eucharist is an external sign of the real presence of Christ which is an internal reality in the Eucharist - retaining those accidental features that make it appear as bread, but it is really His Body and Blood.
@Emmapeeler1 you would be correct - probably more like 50-60 years in reality, as (i'm fairly sure) it's a post-Vatican II change!