You picked quite an interesting thing! π I wonder what the "funky" thing is. Any fermented stuff loses sugars to the bacteria, but doesn't it also go sour? Like way too sour for a wine? How do you even stop the fermentation at some desired point?
Discussion
You can boil it, add acid, or in some cases add salt. It depends on what is doing the fermenting.
Sounds like mostly a symbiosis of molds and yeasts with some bacteria as well.
You drop the temperature
This is the most non intrusive one⦠there are some other methods, you can add sulfur dioxide, or you can pasteurize it
I figure first it will get less and less sweet, then it will go sour? That would be my guess.