Friday, February 19, 2010

I love the smell of geosmin in the morning!

I got around to watering the struggling figs in my dark apartment last night and was soon immersed in the scent of geosmin.

The first time I encountered the name of this chemical was in a college microbiology class. We were instructed to choose a prokaryotic microbe, go out and find it in the real world and then give a presentation on our isolated specimen. Kyle and I lucked out with our slime mold-like Myxobacterium - we only had to hunt for rabbit droppings to culture it. One of our classmates finally found his Vibrio in a rotting squid carcass (and then had to use a really complicated culturing medium to get it out!).

The actinomycete pair was giving their presentation when the specimen's Petri plate made it to my row. We were instructed to smell the culture, which was thick with volatile geosmin. It's funny how smells can evoke such sudden, visceral memories. For me, this smell instantly summoned orchid potting bark. It's also the reason some people are disgusted that beets taste like "dirt," and last weekend I detected it in some Thai black sweet sticky rice.

It's amazing how single chemicals can manifest such powerful and complex summaries of our experiences. I remember my old labmate showing off his most recent hexanal sample, which he said smelled like perfume. Its scent immediately struck me with the notion of rotting fruit, which puzzled me as I tried to identify its source.

Bananas!

I would have thought that a single isolated scent chemical from banana would smell as "natural" as banana soda - that our sensory impression of something as complex as a fruit would also be complex - but in this case, a single chemical pretty much summed it up. The same thing happened when he showed my that his octenol sample smelled just like mushrooms (whose volatile emissions, incidentally contain almost exclusively octenol)! Maybe it's true what was reported recently - that humans are incapable of perceiving more than a few chemicals at a time (contrary to the effusions of sommeliers!).

Sometimes there's not really a line between what's "natural" and "synthetic."*



*An alternate example? Howabout the "Grapple," which if rhymed with "apple" gives a better insinuation of it's taste than the long "a" the producer wants you to use. They're just low quality apples soaked in the dominant chemical responsible for the flavor of grapes - and are an abomination that tastes more like "purple" than "grape!"

4 comments:

  1. Matt, Enjoyed this entry. Pretty cool on the essence of scent. I was able to partake in a tasting panel of almonds this past year, and we discussed similar points. I am always amazed on how developed certain senses are - and how we use them in the modern world.

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  2. Very cool! It'd be neat to hear more about that and about how different varieties of almonds are used.

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  3. Maybe you can help me identify the smell of Japanese woodland - strong and musky. I sometimes smell it in the UK and I'm guessing it's fungal. The closest I've found over here was, ironically, in a Japanese style garden, so maybe it's mycorrhizal and came in with the plants. I kinda like it.

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  4. Yeah, it definitely could be. I'm not familiar with it. Redwood forests have a real distinctive smell which I think is mostly due to the conifers themselves and their allied bay laurel.

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