In the production of vinegar, where does the water come from?

I have heard that vinegar production involves these two reactions..

$$\ce{C2H6O {(ethanol)} + NAD+ -> C2H4O {(acetaldehyde)} + NADH + H+}$$


$$\ce{C2H4O {(acetaldehyde)} + NAD+ + H2O -> C2H4O2 {(acetic acid)} + NADH + H+}$$

But I don't see where water comes from as an input into the second reaction. Like if it's added manually or if it's produced by something else.

Note- there was an additional part of the question which i've since removed.. some of that is addressed https://biology.stackexchange.com/questions/56995/do-acetic-acid-bacteria-use-the-electron-transport-chain-when-converting-ethanol

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    $\begingroup$ In biochemistry, you typically have plenty of water around. $\endgroup$ Commented Feb 27, 2017 at 12:46
  • $\begingroup$ Vinegar is made in a fermentation process of grape juice (short version). Now take a wild guess where the water comes from... $\endgroup$
    – user37142
    Commented Feb 27, 2017 at 12:48
  • $\begingroup$ ok thanks, i've edited my question accordingly $\endgroup$
    – barlop
    Commented Feb 27, 2017 at 13:37
  • $\begingroup$ I think this is relevant bbc.co.uk/schools/gcsebitesize/science/triple_edexcel/… ethanol + oxygen → ethanoic acid + water C2H5OH (l) + O2 (g) → CH3COOH (aq) + H2O (l) <--- (CH3COOH being ethanoic acid / acetic acid / C2H4O2 which is key to the production of vinegar) another related- chemistry.stackexchange.com/questions/33135/… $\endgroup$
    – barlop
    Commented Feb 28, 2017 at 3:24
  • $\begingroup$ @Jan i've removed the additional aspect. $\endgroup$
    – barlop
    Commented Mar 12, 2017 at 20:55

1 Answer 1


Life on Earth evolved in aquaeous solutions. Cells are made up mostly of water; most cells are approximately $70~\%$ water. Water is thus ubiquitous in biochemical reactions. Only few enzymes go great lengths to explicitly exclude water from active sites to prevent undesired side reactions.

Concerning the production of vinegar, that usually starts from some kind of liquid mixture — e.g. wine — which has a high water content. The initially resulting alcoholic solution is also very aquaeous. As stated above, there is ample water.

  • $\begingroup$ Thanks. . I understand there are these two reactions too bbc.co.uk/schools/gcsebitesize/science/triple_edexcel/… ethanol + oxygen → ethanoic acid + water and ethanoic acid + ethanol <--> ethyl ethanoate + water Is the water produced by those reactions a lot less than the water in the wine? $\endgroup$
    – barlop
    Commented Mar 3, 2017 at 11:58
  • 1
    $\begingroup$ @barlop Yes. That water is at best equimolar to ethanol/acetate. Alcoholic fermentation rarely produces more than $15~\%\ \mathrm{v/v}$ and alcohol is less dense and has a higher molecular weight than water so less moles of alcohol give more volume than water. $\endgroup$
    – Jan
    Commented Mar 3, 2017 at 20:44
  • $\begingroup$ and by alcoholic fermentation, you mean the reaction(s)/process(es) that takes alcohol as input and produces acetic acid? (as opposed to the one that takes sugar as input and produce alcohol) $\endgroup$
    – barlop
    Commented Mar 3, 2017 at 21:45
  • $\begingroup$ @barlop I meant the process that takes sugar and produces alcohol – the process typically used to create the substrate of vinegar fermentation (the one that produces acetic acid). By the way, alcohol concentrations at which the reactions you mention would become significant with regard to water production are those concentrations that no known organism is capable of surviving in. $\endgroup$
    – Jan
    Commented Mar 3, 2017 at 21:50
  • $\begingroup$ thanks, also.. I have read en.wikipedia.org/wiki/Acetic_acid_bacteria "Some genera, such as Acetobacter, can oxidize ethanol to carbon dioxide and water using Krebs cycle enzymes." I normally associate krebs cycle with respiration and the electron transport chain. Would I be correct in thinking that this oxidative fermentation reaction ethanol+O2->acetic acid + water, is not respiration, it does not use the electron transport chain? $\endgroup$
    – barlop
    Commented Mar 4, 2017 at 3:46

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