My point is, grapes that start to ferment on the vine are rotten, full of bacteria.
That's a conclusion to which you've come
by engaging in eisegesis. You have an
a priori belief that fermentation is
bad, and you're looking for justification for that belief. Three hours ago you didn't know that yeast occurs naturally on grapes. Now you're explaining your interpretation of Isaiah 65:8 on the basis of some Google page that tells you harmful bacteria
may get into grapes on the vine. That's true, but God's word says, "There may yet be a blessing in it."
Instead of trying to redefine the passage based on outside information, let Scripture interpret Scripture (where have I heard
that before?). The verse is a perfect parallel of Abraham's discussion with God in Genesis 18, and there is no way to infer that Isaiah 65:8 is referring to bacterial rottenness rather than yeast-induced fermentation without a pre-existing bias.