My last two bike rides this week were infused with the smell of brewing beer. My bike route begins at a location between Kentucky Ale and West Sixth Brewery. I do not like beer but I do like that distinction smell of malted cereal grains and hops. Seeing as how the local waters are famous for producing Kentucky Bourbon (too many of which there are to list but many of which are not the sweet southern whiskey I used to associate with the local product), I am not surprised the local craft breweries are abundant and (according to beer drinking friends and families) tasty.
The signature odour I associate with beer brewing comes from the malting and mashing in which complex starches in grains (usually barley b/c of its high enzyme content) are ultimately converted to simple starches (e.g., sugars). Over 200 compounds have been identified as contributing the odour of malted barley (including alcohols, aldehydes, and ketones) . The strongest odour signatures from malted barley are methylbutanals (3 and 2). 3-methylbutanal is described as smelling malty (as expected) but also as fruity, like chocolate, sweet, bready, and toasted. 2-methylbutanal has the same descriptors but is also associated with the smell of roasted cocoa. There is a low and high threshold for the malt scent imparted by the methylbutanals (too low or high and they aren’t detected or as prominent).
The Smell of Evolution 