Fermentation of different types of sugar
Micro-organisms eat the sugars then excrete all sorts of compounds. Acetic acid and/or ethanol is commonly excreted by anaerobic organisms.  Anaerobic organisms can derive energy from multiple reaction paths, even within the same micro-organism (consider the case of facultative anaerobes.)  

Since the same organism can use different paths to derive it is quite natural to assume what comes out is naturally affected by what goes in.