My friend Paul writes:
Here’s a question that hopefully won’t tax your superior barista knowledge banks too greatly. A co-worker of mine once mentioned that occasionally brewing coffee smells like tuna fish to him. I thought that was odd until I noticed it too. Now it doesn’t happen all the time, but sometimes when I smell brewing coffee there is a distinct odor of tuna. I’ve done a google search and found other people who have had this experience, but I’ve found no satisfactory explanation.
My guess is that somehow it’s related to the chemical trimethylamine, which is what gives fish a “fishy” odor. The chemical has an extremely low odor threshold, so it can be detected by scent even in very low concentrations. But what could be producing the trimethylamine? Do you have any idea what could be causing this?
I have no idea, actually. I checked my copy of Illy and Viani’s Espresso Coffee, a collection of scientific papers about coffee, and couldn’t find anything on it. A table reviewing odor compounds found in ground coffee doesn’t include trimethylamine. The compound with the closest description is probably methanethiol, which leaves a “putrid, cabbage like” sense impression.
Another possibility is that the coffee with that smell was stored improperly and picked up off flavors from something else. Any other ideas?
[Cross-posted at STC.]
Not to cast any aspersions on the quality of coffee your friend drinks but fish like odours are often the result of the oils turning rancid. Certainly a possibility if the coffee is old or the brewing equipment badly cleaned.
Comment by James Hoffmann — May 16, 2007 @ 6:28 pm
Thanks, Jim.
Comment by Jacob Grier — May 16, 2007 @ 10:40 pm
Although trimethylamine is one compound that gives fish a “fishy” odor, it is by no means the only one. Trimethylamine is also found in all fish (as far as I know) not just tuna, and the aroma of canned tuna is very different from the aroma of, for instance, fresh tuna sashimi, let alone the aroma of a completely different fish such as salmon, or catfish. I suspect that coffee and fish do have a good many aroma compounds in common, though perhaps not usually in very high concentrations. Canned tuna may specifically gain some compounds that fresh fish does not have, and perhaps some of these are present in coffee.
Either way, it’s an interesting concept for a flavor pairing. Maybe I’ll try a fish and coffee meal some time.
Comment by Barzelay — May 17, 2007 @ 12:51 pm
I bought some of the Starbucks Bold Coffee and it has that “fishy” smell…I keep th beans in the freezer and it’s only been 2 weeks! Ther is only ice and fruit in there…so it couldn’t have picked up any wierd flavors from there. And I thought toring the beans in the freezer was the best was to keep them…?
Comment by Hazelyn — January 25, 2008 @ 12:21 pm
Hazelyn,
The smells might have come from the refrigerator, or perhaps you just got a bad bag of coffee. In any case, taking coffee in and out of the freezer can damage the beans. Your best bet for coffee storage is to keep it at room temperature in a sealed container and use it within a couple weeks of roasting. Unless you have some reason to store coffee long term, there’s no need to freeze it.
Comment by Jacob Grier — January 28, 2008 @ 11:30 am
Regarding the coffee smells like fish comments, I too found a bag of coffee smelling a bit like fish (it was dark roast organic). I searched and came across this blog. I also found a coffee company called Trager Brothers Coffee which sells coffee online. One of their products called Dark Roast Sumatra is listed with the comment “PS if it smells like fish when you grind it, then you got the good stuff.” I could not find any other references to fish and coffee that had any logical answers.
Comment by Jen Gamache — October 13, 2008 @ 5:48 am