Ingredients of an all-natural banana (Blogroll)

I have previously mentioned Melbourne chemistry teacher James Kennedy and his clever educational posters. The poster below (click to zoom), which gently makes the point that “chemicals” are not necessarily harmful, has now gone viral. Similar posters are also available for other foods, and the posters are also available in the form of T-shirts and other merchandise. Take a look!


Kitchen chemistry: esters

Our previous kitchen chemistry post discussed acids, particularly the acetic acid in vinegar (and its reaction with sodium bicarbonate):

Acids like acetic acid, with a structure that looks like X–COOH, are also important because they react with alcohols (with a structure Y–OH) to form compounds called esters. The reaction is X–COOH + Y–OH → X–COO–Y + H2O. For example:

Esterification reaction

Industrially, strong acids are often used to make this reaction happen, but biologically, enzymes do the job. The combination of acetic acid and ethanol is ethyl acetate (used in some nail polish removers), and the image below also shows isoamyl acetate and geranyl acetate. Each ester has the same X–COO–Y structure:

Various esters

Esters have a “fruity” smell, and indeed the odour of fruit is largely a result of a mix of various esters (go on, sniff some fruit, and celebrate the complex odours that you smell!). Synthetic fruit flavours likewise use esters, but typically in a simpler mix that never smells quite like the real thing.


James Kennedy has produced this wonderful infographic of esters and their smells (click on the thumbnail to zoom):