how does alcohol turn to vinegar

im a cider maker and ive read several threads about how if you dont sanitize properly or if you dont keep oxygen out of your cider it will turn to vinegar.

1) how exactly does alcohol, such as cider or wine, turn into vinegar

2) what factors cause wine or cider to turn into vinegar, (ex: oxygen contamination, bacterial contamination)

im a chemistry major so an explanation at the molecular level would be nice

Bacteria turn ethanol into acetic acid.

C2H5OH (Ethanol)+ O2 → CH3COOH (Acetic Acid) + H2O


Acetobacter + oxygen = bad for beer

Certain bacteria (like acetobacter) ferment ethanol into acetic acid.

C2H5OH + O2 → CH3COOH + H2O

So good sanitation and keeping things anaerobic prevents beer and wine from becoming vinegar.

cshamilton said:

Certain bacteria (like acetobacter) ferment ethanol into acetic acid.

C2H5OH + O2 → CH3COOH + H2O

So good sanitation and keeping things anaerobic prevents beer and wine from becoming vinegar.

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And aceterobacter only can make vinegar when both alcohol and oxygen are present (as shown in the formula). That's why it's important to sanitize, as well as top up carboys to prevent oxygen in the headspace.

wow, thanks for the fast feed back.

i was worried because i have a batch of cider brewing in a bucket with around 2-3 inches of head space and its fermenting so slowly (less than 1 point a week) that ive been worried about O2 contamination turning my cider into vinegar. but since im good with sanitation im not to worried now.

kamkamdac said:

wow, thanks for the fast feed back.

i was worried because i have a batch of cider brewing in a bucket with around 2-3 inches of head space and its fermenting so slowly (less than 1 point a week) that ive been worried about O2 contamination turning my cider into vinegar. but since im good with sanitation im not to worried now.

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Well, oxygen is a danger once you get to about 1.020 or less, especially if it's going that slowly. What's the current SG?

yooper said:

well, oxygen is a danger once you get to about 1.020 or less, especially if it's going that slowly. What's the current sg?

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1.015, i want it to drop 3 more points before bottling.

kamkamdac said:

1.015, i want it to drop 3 more points before bottling.

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It might drop more than 3 more points if it's not done, depending on yeast strain and the OG. And then you could have bottle bombs if you're not careful.

most of the ciders I have done have finished close to 1.0, and had one actually go below. Be very careful if you bottle at 1.015

Yooper said:

It might drop more than 3 more points if it's not done, depending on yeast strain and the OG. And then you could have bottle bombs if you're not careful.

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planing on pasteurizing to stop fermentation at about 1.010. going to use a pop bottle to judge carbonation to tell when to pasteurize.

i want to stop it from fermenting to dry to cut down on aging time.