Friday, 15 January 2010

Flavour Compound of the Week – Ethanol


Ethanol or ethyl alcohol is what chemists call alcohol. Ethanol is formed when yeast ferments sugars. As you can see at an atomic scale, ethanol looks like a chubby balloon dog pissing against the wall.
Ethanol is perfect for illustrating the three key factors in flavour compound detection. Our ability to smell a smell in beer is mainly dependent on three things: the substance’s concentration, its volatility and its flavour threshold. Despite being plentiful in beer (around 40,000 parts per million in a 4% ABV beer) ethanol is not easily detected until the beer gets above 5%. Methyl mercaptan (rotten cabbage flavour) on the other hand is easily detected at 0.00002 parts per million. The reason for this is that methyl mercaptan is much more volatile and has a far lower flavour threshold. The flavour threshold is the concentration of the smelly compound in the beer at which the average nose can detect it. It is likely that we will have evolved to be able to detect certain smells rather than others because they are poisonous and should be avoided. Hence alcohol can't be quite as bad for you as the Daily Mail suggests. Volatility refers to the ease at which an aroma compound escapes the beer and flies up your nose. Highly volatile substances fly off very easily, less volatile substances need to be shaken or swirled out of the drink.
Anyway, the best way to describe the aroma of ethanol is to say that it smells like vodka. On the palate alcohol has a warming effect. You can literally feel the strength of the drink in the mouth and the nose.

4 comments:

ZakAvery said...

Stuart, could you say a bit about why you use open fermenters, and how this relates to the profile of volatile aroma compunds in your beer?

Whorst said...

Stu, you need to do a piece on yeast, and it's effect on beer. Some people don't believe yeast plays a critical role in flavor.

Stuart Howe said...

Gents, I shall indeed cover both subjects in the near future. I think that drinkers should understand that there is more to beer flavour than a set of raw materials and a few flashy processes like oak aging or extended lagering. The flavour of beer is like a sculpture with each process variation like another tap of the brewers chisel. Beautiful poetry on a Sunday evening.

mewmewmew said...

The flavour threshold is the concentration of the smelly compound in the beer at which the average nose can detect it. It is likely that we will have evolved to be able to detect certain smells rather than others because they are poisonous and should be avoided.


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