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Issue 91 - In praise of ester

Whisky Magazine Issue 91
October 2010


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In praise of ester

Ian Wisniewski asks how are esters created and what do they contribute to malt whisky

sters are renowned for contributing fruityness, such as apples, pears and bananas. Esters are created when alcohol and acid molecules interact and integrate with each other, which occurs during the fermentation, distillation and maturation processes.

During fermentation yeast metabolises (digests) sugars in the wort (the sugary liquid produced by mashing). A small amount of these sugars are broken down by the yeast into acids, a vital process as yeast requires acids in order to grow and reproduce. These are termed either organic acids, as they're derived from malted barley, or fatty acids, which is a more specific reference to fats in the malted barley from which the acids originate.

Yeast produces different types of acids, beginning with short chain fatty acids, so called because each molecule typically comprises two carbon units linked together.

Yeast subsequently produces medium chain fatty acids (around 6 to 10 linked carbon units) and long chain fatty acids (around 12 to 16 units). However, it's short chain acids that are produced in the greatest quantity.

Meanwhile, most of the sugars are broken down by the yeast into different types of alcohol.

The alcohol produced in the greatest quantity is ethanol, which is a short chain alcohol as each molecule comprises two carbon units linked together.

The consequence of yeast producing alcohol and acid is that molecules of each are present within yeast cells, where complex interactions between these molecules sees them int...

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