What makes a grape ferment?

I know why it ferments, but was wondering if there was a specific chemical that caused this reaction to occur.

Nothing fancy; the yeasts on the skin comes in contact with the grape sugars, which gets converted into ethyl alcohol and carbon dioxide. Sometimes cultured yeast is added by winemakers to help the process along.

Can you write out the chemical reaction by any chance?

Glucose -> Glucose 6-phosphate -> Fructose 6-phosphate -> Fructose 1,6-diphosphate -> Glyceraldehyde 3-phosphate (2 molecules) -> 3-Phosphoglyceroyl phosphate (2) -> 3-Phosphoglycerate (2) -> 2-Phosphoglycerate (2) -> Phosphoenolpyruvate (2) -> Pyruvate (2) -> Acetaldehyde (2) -> Ethanol (2).
Here’s the first part of the pathway through Pyruvate, and here’s the conversion of Pyruvate to acetaldehyde, then Ethanol.

Another way to put it is the way writer Kurt Vonnegut did in his novel Breakfast of Champions. The yeast injests the sugar and excretes alcohol. Vonnegut described a scene in a bar as people “sitting around drinking yeast excrement.”

That’s much more romantic sounding :stuck_out_tongue: