Practical investigations
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I’m investigating the chemical composition of wines for my project and I have discovered a problem. I have come across one website which briefly mentions that the tannin content of wines can be calculated titrating the wine with potassium permanganate. There was no further explanation and I am curious about this topic. Could you explain in slightly more detail please? Thanks.
Igloo writes ...
Tannins are complex phenols, and since phenols can be oxidised to compounds known as quinones, it is reasonable to assume that their concentration can be estimated using some sort of redox titration. About 100 years ago an analyst known as Lowenthal patented a method using potassium permanganate, and this has been used successfully ever since to measure tannin concentrations in the laboratory. Given that there must be other “oxidisible” material in wines apart from the tannins, I would imagine that more specific and accurate techniques exist today.
I have come across a cider tannin analysis website which describes the practical technique in detail, and you may wish to have a look at it.
If you use Google (www.google.co.uk) with phrases such as “analysis tannin permanganate” (without the inverted commas), you may well come up with other useful web references.
It should be possible to adapt this method to your needs with your wine samples, provided that you can get hold of the redox indicator “indigo carmine”. Incidentally you would be carrying out experiments which are relatively unusual - I have not yet heard of anyone analysing wines for their tannin content.
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Risk assessment
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updated: 09 April 2008
