I've had several coffees from Rwanda, all bourbons or bourbon variants and noticed some of these coffees have a leguminous, garden pea, winter green, almost earthy taste to them which is not to my liking because it doesn't taste 'clean'. (fyi/fwiw I dislike wet hulled Indonesian coffees)

I am aware of potato defect, but this doesn't taste/smell quite like that. It is much more subdued, whereas Potato you can tell right when you grind it and it's intense raw sprouted old potato and yuck.

I've had bourbons grown in central america as well as some cleaner Rwandan coffees and they don't have this taste. Does anybody have an idea of where this comes from? Processing defect?

faustroll wrote: I've had bourbons grown in central america as well as some cleaner Rwandan coffees and they don't have this taste. Does anybody have an idea of where this comes from? Processing defect?

I've been noticing this in my Kigeyo from Rutsiro. Not every cup, and never as loud as Potato. I have no answers.

I'm sipping on some of Marshall's Kigeyo right now. This is my fourth cup or so. As soon as the beans hit the grinder tonight, I knew something was different. Garden pea. Will never forget that aroma from the Nez du Café set. Hopefully it won't be there for cup #5!

Update: wasn't there this morning with the Kigeyo. I'm happy that whatever it was didn't affect the rest of the bag, as far as I can tell.

I've been getting this garden pea note in some Rwanda Lake Kivu I roasted up and been puzzling over if this is the potato defect or not. Sometimes, I can tell right away when I grind that it's going to be strong, and sometimes not. This quote from the Dallis Bros. Coffee Blog makes me think it may be the dreaded potato defect after all.

The chemical is actually closer to snap peas than potato from the "Le Nez Du Cafe" aroma kit many of us calibrate with.

I've really relaxed my pre-roast culling, but I'm thinking that I'm going to spend more time checking the green coffee before roasting for Rwanda and Burundi coffee and maybe start using my UV flashlight again.

My Le Nez Du Cafe notes say that the chemical compound giving rise to garden pea aroma is 3-Methoxy-3-isopropylprazine, and searches reveal that this pyrazine is involved in the potato defect, and also the smell of bell pepper and other vegetate smells, etc, so I think that what I'm picking up is the potato defect, just with a twist on the aroma. Here's some links:

Peter Giuliano on The Rwandan Potato problem on Coffeed

The Borlaug Institute Takes on the Potato Defect

Sweet Maria's on Rwanda

I found a lot of interesting looking articles using Goggle's Scholar search with search terms of the chemical compound, or pyrazine and coffee, but not having the proper subscription, I could only browse the first page of these articles.

I found a company, Pyrazine Specialties, in Georga, that serves the flavor, fragrance, and pharmaceutical industries. Their catalog and Introduction to Pyrazines contains some interesting information about pyrazines and other compounds as well.

Also of interest is the LRI and Odour Database specifically the Odour Database where you can look up chemical compounds associated with common odor descriptions. It's interesting to note that for any given chemical compound, there are usually several different food items related to that compound, likely due to differences in concentration and in combination with other compounds.

Also interesting is this Optimization of roasting conditions for high-quality Arabica coffee article in the International Food Research Journal which concludes that "volatile flavours compounds; 2-methylpyrazine and 2,5-dimethylpyrazine are the marker compounds that contribute to Arabica coffee flavour. Therefore, the optimized condition (time and temperature) for roasting of Arabica coffee beans is at temperature of 167.68°C for 22.50 min." The article is interesting, not for the conclusions, but more for the study of the chemical compounds. It's clear that the researchers know a lot more about the compounds than about roasting coffee.