The reason Jesus turned water into wine, according to my biblical dictionary, was that in the olden days wine was fruit juice.
Whoever told you this was just plain wrong. Without pasteurization it is literally impossible to prevent grape juice from fermenting. I am a PhD chemist and I can confirm for you scientifically that this is the case. It is impossible to prevent yeast from entering grape juice without modern technological innovations and yeast always does its work. Without refrigeration, grape juice will ferment within just a couple of days. It was literally impossible to drink unfermented grape juice except for a narrow window of time of a few weeks around the time of grape harvest. So…. Whoever told you this was mistaken. By the way, the wedding at Cana was probably in the Spring, based on the context, whereas the grape harvest was in the late summer or early Fall. So, the wine served at this wedding was alcoholic. Of course, it is possible that Jesus made grape juice rather than wine, but the language used and the statement of the one putting on the wedding feast that it was very good wine seems to imply that the wine Jesus created had alcohol in it. I would not push this claim too far, as there is no proof either way. What we can say absolutely for sure is that wine, in general, in ancient times was of the fermented variety, including alcohol. Unfermented grape juice spoils and becomes undrinkable without the alcohol content within just a very few days by he action of bacteria, especially in the warm climate conditions in the Near East.
Apparently, you are reading things written by people who believe that all alcohol drinking, even in moderation, is sinful. I am strongly against drunkenness, as are all Christians, but the fact is that Jesus and the apostles and the early church drank fermented grape juice, presumably in moderation. Paul recommended this to Timothy, and he did not restrict his advice to the one month or so in which unfermented grape juice would be available. Most likely, he suggested this because of the “medicinal value” of wine, which does not even apply to grape juice. I am sorry, but you may have to change your opinion on this.