The Bible refers to Jesus creating wine and drinking wine. Many Protestants say that "wine" doesn't refer to wine, it means grape juice. This despite the clear tradition of Catholics, Orthodox and Orthodox/Lubavitcher Jews going back forever. It's not even a valid Passover meal or Eucharist with grape juice.
They take the clear word "wine," then translate it into something ambiguous like "fruit of the vine," and then construe the ambiguity to mean grape juice. (No different than taking Jesus is "God," then interpret God to mean "heavenly," and then say he's just an angel.)
Jesus talked about being "born again." He said you need to have a spiritual "new wineskin," because an old wineskin can hold old wine but new wine will cause it to burst; new wine requires a new wineskin. Why? Because the wine is releasing gas as it finishes fermenting, and the old wine has completed the fermentation process. The Bible says a good Christian will not drink too much wine; strange that it would matter how much grape juice you drink.
They did not (fundie beliefs notwithstanding) have access to the Welch pasteurization process that was unveiled at the very end of the 1800s.