For one thing, Methodists just get grape juice, but Catholics get the Body, Blood, Soul and Divinity of Christ. Something no Methodist would even claim.
I'm not defending the UMC because it has been circling the drain for most of my lifetime, even though I came from 5 generations of (real) Methodist Episcopalians, many of whom are spinning in their graves at what UMC has become. (I've since found a church that practices the apostolic faith.) Nor can I claim to have read Wesley's precise instructions about communion. But what I was taught in childhood is that Methodism uses grape juice because of its founding strength in the temperance movement in England and the US, and that there is nothing specific in the Bible requiring fermentation. I've also heard that they believe the taking of the wafer and "wine" is symbolic, that the elements nourish one's body, and a communicant is part of the Body of Christ, ergo, by taking it one is then part of the Body and Blood.
The church of which I am now a communicant believes that because Christ said "Do this in remembrance of Me," and "this IS my body; this IS my blood," that they actually are His Body and Blood at the moment you take them—because He said so. Like the RCC, the LCMS disapproves of any taking of the eucharist unworthily, and has procedures in place concerning that.