The word we translate wine is a word better translated “fruit of the vine”. Two thousand years ago if you asked for a glass of wine and did not specify as to a type you could be served; grape juice, reconstituted grape juice, sweet wine (with a little alcohol) and a wine much like what we call wine today.
Reconstituted Grape juice was the most expensive. Carefully removing part of the water from the grape juice turns it into syrup that will not spoil or turn to wine in a cool place like a cellar. This syrup is still produced today and is how most large quantities of grape juice are shipped.
Two thousand years ago a poor person, especially in spring or early summer, could not afford grape syrup and fresh grape juice was not yet available so the only choice would be wine, wine that would make people drunk.
Jesus was at a party of poor people. These people were so poor that they were running out of cheap, alcoholic wine. Jesus asked that the large vessels be filled with water. When the water was poured out it was “the fruit of the vine”. It would fit that it was reconstituted grape juice. The people who had just filled the vessels with water may have assumed the syrup had already been added. The question asked was, “why did you save the best wine for last?” Not, “how did the water turn to wine”.