82. Potato Taste Defect - the re-SEARCH continues

April 25, 2018

Coming out of the whirlwind of meetings and new information at the Specialty Coffee Association

Dr. Susan Jackels of Seattle University

Expo, April 19 - 22 at the Washington State Convention Center in Seattle, I was grateful I had planned a quiet lunch with a faculty friend, Dr. Susan Jackels. Jackels teaches chemistry at Seattle University. We first crossed paths at the International Coffee Symposium in Kigali, Rwanda back in March 2014. For those that may not know, that was the first public recognition by governments in the region that potato taste in coffee is a real issue. Despite the fact that researchers had identified the unpleasant, raw potato taste in coffee in the 1960s, officials allegedly had been encouraged to avoid giving the taste a specific name, traceable to specific countries.

The Cup of Excellence competitions in 2012 and 2013 are often given credit for bringing the problem so clearly into the light that public forces could unite to find a common solution. Researchers from around the world, including Jackels, were invited to Kigali. Leading up to that conference and since that time, Jackels has been on the chemistry fore-front of fighting the "potato taste problem" in coffee.

"Potato taste defect is the hardest problem I've ever worked on," she told me over Mex-Asian fusion tacos at the Athenian restaurant at Pike Street Market.

This is a weighty statement since Jackels is near the end of her university career. (Fortunately, she plans to continue researching after formal retirement.) She has successfully solved daunting problems, tackling fermentation issues with coffee farmers in Nicaragua in the early 2000s and then supporting an initiative for her university to become one of the first fair-trade universities, back when even the students were skeptical! (They finally achieved FT status in 2014.)

I asked Jackels, "what are some of the key learnings about the potato taste defect that we have today?" Here is a summary of what I, as a lay-person, took away. Please consume these bullet points with caution! There are scientific papers published by Jackels and others on these topics.

• The potato taste and smell is caused by a pyrazine molecule, 3-isopropyl-2-methoxypyrazine, “IPMP” for short, to which humans are highly sensitive. IPMP is also present in rotting food, it’s part of “putrification”, so that’s why humans are sensitive. Our systems have developed to ‘detect and reject’.
• There are probably trace amounts of IPMP in all coffee.
•  IPMP has been found in wine, and it’s bad when it’s at high levels there, also.
• Coffee plants in extreme stress seem to produce more IPMP molecules, trying to ward off the danger. Similar to insect repellent. So stressed coffee plants (e.g. those bitten by Antestia) may have 1000x the normal levels of IPMP and the human nose (and tongue) can detect this.

She shared the direction she sees things going in terms of detection and prevention.
Detection in green coffee: one of her Ph.D. students (Mateus Montenegro) did an experiment with landed green coffee from Rwanda and Burundi. Using gas spectrometry he tested whether IPMP levels were higher in less dense coffee beans (inverse relationship). He found this to be the case for the 1200g (~2.5 lbs) samples he had. Noteworthy is the fact that identification of the potato taste smell was done by a trained  human.

"The human nose is the best tool for detecting PTD," Jackels says. She worked together with coffee companies for awhile to develop an "e-nose" and said it just cannot compete with the sensitivity humans have to the IPMP odor. "Also, hydrospective imaging has been shown to not work as well."

Prevention of PTD: Jackels advises the following as practices that will give the greatest likelihood of reducing PTD incidents in roasted coffee being given to consumers. 100% elimination is still considered unlikely.

1. Soil management with “sweet” (fresh) mulch is key for reducing PTD.

2. Floating cherry, since less dense beans are more likely to be beans damaged by Antestia and therefore containing high levels of IPMP.

3. Hand sort while the beans are wet, it’s easier to see and remove the damaged ones.

4. Eliminate damaged beans at the soak stage, too.

The uncertainty around prevention techniques is what continues to lure Jackels and many other researchers to pursue answers to the problem.

• Joseph Bigirimana is a Ph.D. candidate at Michigan State University working on an entomology thesis that promises to have many helpful insights. 
• Dr. Daniel Rukazambuga at the University of Rwanda has been pursuing support for field research on the topic since before the 2014 conference. His efforts won him the role of leading the effort on 64 coffee study fields during the Feed the Future Africa Great Lakes Coffee (AGLC) support program, 2015 - 2017 (USAID funded). Results from that research will be presented at the upcoming end-of-project workshop, June 26, in Kigali. 
• Two researchers in Burundi, Dr. Bonaventure Minani at the University of Ngozi and Dr. Gustave Nkurunziza at Gitega Polytechnic lead 32 study plots each for the half of the AGLC project taking place in Burundi.
• Read more about the AGLC program: click here.

So clearly, there is still a lot to learn, and a lot happening to "reach" a better understanding of how to prevent potato taste defect.

Views not to be missed when at Pike Street Market: