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Science Society learns the chemistry of wine

On 9 October the Science Society welcomed Luke Bartlett to give their first lecture of the school year on the Chemistry of Wine. 

The origins of wine are lost in legend and involve the storage of grapes in cellars that fermented naturally and produced a delicious liquid but some lethal gases.  The liquid produced is very complex with up to 2,000 different chemicals.  

We can start with water, ethanol, other alcohols, esters, aldehydes, ketones, acids etc. Luke Bartlett took us on a tour of the effects and significance of a wide range of them. Over 500 can affect the flavour, hence the exotic descriptions that are used because some of the flavours do appear in unusual substances, like cat urine! The flavour alters over time as the chemistry in the bottle is constantly changing. Tasting involves some bravery in declaring which flavours are present, identifying fruits, flowers and more exotic examples. There is significant subjectivity in the process, judging by the reviews of the wine we tried from a range of experts. Some bad flavours can develop due to bacterial action, such as the taste of mouse urine and various sulfur compounds. Preservatives like sulfur dioxide have been used since the fifteenth century but their levels are strictly controlled.  

Having tried a dry wine we were then led through the development of sweet wines, from cheaply adding sugar to late harvest and ice wine and noble rot, where a mould forms on the grapes and develops the flavours of wines like Sauterne.  We then tasted an orange Muscat to enjoy some marmalade, honey and apricot flavours. Richard Feynman famously said that understanding the function of the parts of a flower in no way detracts from its beauty.  Understanding the chemistry of wine can only add to the enjoyment of its flavours.