The new wine is grape juice when it goes into the bottle, and yes eventually it will ferment if the bottles worn out and aren't sealed properly. But if the bottles are new and sealed properly the new wine wont ferment and pressure wont build up in the bottle so both the bottles and the new wine are preserved.
Luke 5:37-38 KJV
And no man putteth new wine into old bottles; else the new wine will burst the bottles, and be spilled, and the bottles shall perish. [38] But new wine must be put into new bottles; and both are preserved.
Bottles are earthen vessels and this treasure is hidden in earthen vessels... the wine skin translation kind of ruins the parable, it makes it harder to see the true meaning of the parable. The old bottles were Jews, the new bottles are the Gentiles.
It looks like your KJV has limited your understanding here; you have this exactly backwards. The "wine skin" (KJV: "bottle") is exactly that: a skin bag. The modern sense of "bottle" is not correct; you are making the mistake of anachronism: reading a modern meaning into a 17th-century word.
Further, you seem to be unaware of what happens to grape juice if it is not chemically or thermally preserved. It will ferment because of the chemicals and biological agents present. A tight seal on a modern bottle will not prevent that; more likely the bottle will burst. Your view would have modern pressure seals available in 1611 (or 30 AD)... a bit optimistic, considering that the amount of gas produced would raise the pressure a thousand-fold in the tiny air space. Good luck keeping that cork in.
The verse makes perfect sense if the grape juice ferments inside a still-flexible new skin. By the way, the new bottles are not Gentiles (necessarily); they are people who receive the Spirit of God by faith in Christ.