The science of alcohol
The science of alcohol

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The science of alcohol

2.2.2 Vinegar from wine

If you have ever had the misfortune of ordering a bottle of wine that is ‘corked’, the beverage will taste of vinegar – a clear sign that it is off and not worth drinking.

The reaction here is again between ethanol in solution and oxygen gas, but this time the outcome is different:

equation left hand side cap c sub two times cap h sub five times cap o times cap h times prefix plus of cap o sub two equals right hand side cap c times cap h sub three times cap c times cap o times cap o times cap h plus cap h sub two times cap o
(Eqn 1)

Activity 1 The chemical formula for vinegar

Timing: Allow approximately 5 minutes for this activity

What is the correct chemical formula for vinegar (also known as acetic acid)?

a. 

CH3COOH


b. 

CH2COOH


c. 

CH4COOH


d. 

C2H5COOH


The correct answer is a.

Discussion

If the beverage tastes of vinegar, then the vinegar must be a product of the reaction shown above. You learned in the previous section that H2O is the formula for water. Therefore the formula to represent vinegar must be CH3COOH. This is in fact a substance known as acetic acid. Note that you can simplify this formula to CH3CO2H, both versions of this formula are correct.

This reaction is not one that occurs spontaneously. It requires the presence of a bacterium called Acetobacter which uses this reaction to gain energy for its own biological processes. Acetobacter must be prevented from growing in wines and turning them to vinegar, and so wine must be bottled in very clean conditions, air must be excluded by good corking, and a preservative, sulfur dioxide, is usually added. When a bottle is ‘corked’, the seal has been broken, allowing bacteria and air in.

However, note that the same process is encouraged in some circumstances to produce ‘wine’ or ‘cider’ vinegar. This is a good example of how the ‘ill-effects’ of nature can also be used to some benefit.

A further chemical reaction takes place when ethanol is fermented – a reaction which allows us to produce an alcoholic drink.

SOA_1

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