Practical investigations
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I am doing an investigation into the differences between red and white wine. I will be looking into the SO2, alcohol and acidity of wine. I need to write what I expect to see, however I have no knowledge of what the chemical differences are and every time I look on the internet I just get told the differences in taste, appearance etc. Please could you explain the differences between them and if possible books or articles I can use for extra information. thank you.
Igloo writes
The first thing to point out is that the chemistry of wines is extremely complex, and you are unlikely to find many web references relevant to your enquiry. All I can say is that the longer the grape juice is in contact with the grape skins during the grape-pressing process, the redder will be the colour of the wine. This darker colour of red wines derives mostly from phenolic compounds of the tannins in the grape skin.
All this means that I doubt if you will find any significant “trends” linking red or white wines with their SO2, alcohol and acids content. However, there will be a difference in the tannins they contain, so I suggest that you include this analysis in your investigation. Tannins, being phenols, are usually determined via colorimetry or by means of a manganate(VII) titration. I suggest that you search on Google to find more information on these techniques.
If you need more help on tannin determination – having found very little for yourself – get back to us and I’ll point you to some relevant web references. I have answered similar questions before for students; search under 'wine' on our web site.
Risk assessment
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updated: 29 January 2008
