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It is my understanding that the fermenting bacteria process the alcohol into acetic acid. But why is it about half the percentage of volume? For example table wine is often 12% ethanol, but vinegar is generally about 5% acetic acid.

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    $\begingroup$ Can you add sources to your claims? As a hunch, enzymes help to swiftly establish equilibria. Enzymes don't push the equalibrium to an end product. Further, the end product may be toxic. Take the fermentation processing during beer brewing - there's a substantial amount of sugar left after the beer is ready. Alcohol is toxic to yeast. $\endgroup$ – AliceD Mar 24 '18 at 20:17
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    $\begingroup$ Not really; i take this claim as a fact of everyday life. Both alcohol and acedic acid contents are indicated on the bottles. German language Wikipedia has a list of aciditys for various types of wine (those alkohol contents are not indicated), but i guess that is no scientific source: de.wikipedia.org/wiki/Essig#G%C3%A4rungsessige $\endgroup$ – HannesH Mar 24 '18 at 20:40
  • $\begingroup$ Yep, makes sense. +1 $\endgroup$ – AliceD Mar 24 '18 at 20:42
  • $\begingroup$ What evidence have you that the wine used for wine vinegar contains 12% alcohol? I would have thought it would more likely be lower alcohol wine made from poorer grapes with a lower must weight (content of natural grape sugar). It is unlikely to bear much relationship to commercial table wines, which are often chaptalized in order to reach the EU minimum alcohol level. $\endgroup$ – David Mar 25 '18 at 18:26
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    $\begingroup$ That the acetic acid always has 5% has the simple reason that it is diluted to this concentration. $\endgroup$ – Chris Mar 25 '18 at 18:58