Yeasts are naturally present on the grapes, there is no need to attract them(Of course, in modern time we are able to separate strains and use the ones that produce the most desired characteristics.) Fermentation is a type of decomposition and so when you say “and eventually ferment” it has already been fermenting. If the grape were already decomposed by other microorganisms, such as bacteria, then there would be no sugars left for the yeasts to ferment.

I would also like to see some links on the methods of preservation that you offered. I do not believe boiling would be a very good method. It would kill any microorganisms already present, but there are still sugars which would then, in this case, attract yeasts or bacteria unless it were sealed in a sanitized, air-tight container. I would also love to learn a method of filtration that could have been in practice at that time that could help me remove yeasts and bacteria from juice.

And of course Jesus could have turned water into grape juice…he can do what he likes. But scripture says it was wine…not grape juice. And everywhere else it refers to it, in the context and use of the time, it is understood to be alcoholic wine – not un-fermented grape juice. There are plenty of reasons it is very implausible that Jesus did not drink alcoholic wine.

My Methodist minister brother in law taught at a Methodist college and would go out of town to buy wine so the locals wouldn’t catch him in the act.

Saint Robert Bellarmine Calling Drunkards To Repentance!

I am confused at what point you are trying to make in your previous post.