Have you ever drank a cup of coffee from East Africa (Burundi, Rwanda, Zambia, etc.) and tasted a distinct potato taste? We at DRC have seen this potato defect for years but have been truly impressed by what the growing specialty coffee production has done for the Rwandan economy and have been equally impressed by the taste of the coffees from there. In order to enjoy this wonderful coffee and support what's going on in Rwanda, this year we've bought another coffee being willing to take the occasional potato defect head on. But, it's caused us to want to take a dig and find out a little more about this defect and give our readers an overview about what's happening. After some digging we've found that the dreadful potato defect is hypothesized to be from microorganisms infecting the coffee bean that could have been transmitted due to damage from insects called Antestia bugs. It is thought that these bugs transmit a chemical from the methoxypyrizine family (2-methoxy 3-isopropylpyrazine) when they feed on the unripe fruit and create a defective bean. There isn't definitive proof that these bugs are the sole culprit. When they burrow into the bean they leave small holes in the fruit where other chemicals could enter but again, that's just a hypothesis. Regardless, the damage that the Antestia bugs create are hard to detect when farming and processing and the final, hideous aroma whether it's from the bugs or not can't be detected often until the coffee is ground. We've talked to some of our friends at Toby's Estate in Brooklyn, NY and they occasionally experience the same thing with this exact Rwandan. It only happens ever now and then, but when it does, it's easy to detect and discard before serving.
A lot of time and research is currently being spent to determine the exact cause for this defect and how it can be prevented in the future. But for now, when you grind an East African coffee, pay attention to the dry aromas before you serve it. If you smell some potato just dump the grounds, purge your grinder and re-brew. It's an unfortunate defect but it's an interesting reminder that we serve an ever changing, highly intricate, agricultural product.
Brew on people.