CCS Report from AFCA 2014: The Potato Defect


For anyone who has worked with coffee from the Great Lakes region—Burundi, Rwanda, D.R. Congo—the so-called “potato defect” has been the source of much frustration. The vast majority of cherry producers within this region are smallholders reliant on receiving premium prices. The average Burundian smallholder owns less than one hectare of land and because of many and varied social-economic-political realities, the small plots smallholders do have is not all dedicated to coffee production, which can be the farmer’s biggest cash earner.

I have heard a lot of speculation about potato throughout the years and was hoping to zero in on some concrete answers, during last month’s African Fine Coffees Association conference, as to what the potato defect is, as well as how it is being fought.

What is known is that potato defect is actually a chemical: isopropyl-2-methoxyl-3-pyrazine. Pyrazines are nitrogen-containing compounds that have unique aromas: earthiness, potato, mould.  Bacteria (thought to be Enterobacteriaceae) make up this pyrazineandthese bacteria are thought to be carried by the Antestia bug. Yes, I realize this language is scientific and vague. It’s because research into the potato problem is young and there are no definitive answers. However, what research has been done (the best research has come from a French agricultural research centre called Cirad) supports the above descriptions of the problem.

The Antestia bug is thought to infect coffee cherries with bacteria as it comes into contact or burrows into coffee cherries. Some of the biggest contributing factors to the elusiveness of the problem are that it is difficult to see infected cherries; infection is random (and doesn’t occur in great amounts); and it does not tend to be obvious infection has occurred until after the roasting process. You can all visualize how many roasted beans go into just one cup of coffee – it only takes one infected bean to ruin the entire cup, rendering it undrinkable due to its unmistakable raw potato/green peas smell and taste.

The Significance of the Problem

As I mentioned in earlier posts about the AFCA conference, most participation came from the commercial coffee world. Although CCS works with the best and brightest producers, making stellar coffees, I feel it is important to know about the commercial side of the coffee trade because its influence on coffee production (how and what) is too significant to ignore. Especially in countries where specialty coffee has not been present for long, as is the case in African coffee producing countries. During the Potato Panel discussion at AFCA this year, speakers included a representative from Alliance for Coffee Excellence (which oversees the Cup of Excellence competitions), a commercial coffee buyer, a specialty coffee buyer and a researcher studying the potato defect.

When commercial buyers choose to work with coffee from the Great Lakes region, they tend to consider and then compare a general profile and quality. For example, Rwandan and Burundian coffees have been compared to Honduran “high grown” coffees quality- and cup-wise. There exists a distinct price differential between what a Honduras “high grown” can command versus what a similar quality coffee from Rwanda and Burundi can fetch. The potential for potato is not the only contributing factor in such a price differential, but it certainly plays a role. According to one panelist’s estimates, the price differential for a Great Lakes coffee is 20-25 USC/lb. less than a comparative coffee. Taking other factors into account (e.g. logistics efficiency of working in the Great Lakes region versus regions like Honduras), the “potato discount” is estimated to be 10-15 USC/lb., adding up to an estimated $6.5 million USD loss each year for a country’s production yield.

In high quality markets like CCS’, prices are not discussed in terms of discounts, but rather premiums. Buyers of specialty coffee reward quality with premiums and as Great Lakes coffees cup uniquely, specially, as well as are harvested at a good time of the year (i.e. in between other countries' harvests), premium prices are paid for coffee gems found in the Great Lakes region. But potato makes it challenging and somewhat risky to work with coffees from this region. Roasting companies spend a lot of resources working with baristas and wholesale clients on how to detect the defect. Some roasters choose to limit how such coffee is used within their menus (e.g. not blending them with other coffees).

What keeps us motivated and focused on working with this region are the fantastic characteristics of uninfected (which is the vast majority of) coffee from this region. We have been working with truly special coffees from the region. These coffees, unlike in the commercial world, cannot be substituted with coffees from anywhere else.

Management strategies

Certain strategies have been employed by farmers and washing stations to mitigate the potato problem. Just because there are not yet definitive answers about the causes of potato, this does not mean that action is not being taken.

At the farmer-level, insect management to mitigate the prevalence of the Antestia bug has been undertaken. In addition, while selective picking is generally good practice, it helps combat potato because infected cherries are mouldy/bacteria-infested. If only ripe, clean, red cherries are sent to the washing station, there is less potential that infected cherries will move further up the supply chain.There is still a long ways to go in farmer education about these techniques but the best washing stations have been working with farmers on these.

Most action has been taken at the washing station (wet processing) and dry mill (dry processing/hulling) levels. Starting with the transport of cherries to the washing station, there have been less potato problems in lots that have been transported more quickly from the field to the washing station. During sorting, floating has been important in that lots that have had less instances of the defect have generally had denser beans. At the dry mill, extensive lot sampling (looking at density in particular) has led to traceability of lots causing more potato problems.

Other technology and strategies include mould probes (which are have also been utilized in Central America for the Roya problem), aromatic sensing devices programmed to recognize defective beans and ultraviolet light sorting. However, due to the fact that these tools are meant to isolate individual beans, they are quite time and resource inefficient.

If it reads like general best agricultural and processing practices should be employed in the battle against potato, that’s obviously true. Even without the defect, these practices should be standard. But it would be a mistake to go so far as to disregard the potato problem as a real and significant issue. In fact, I would argue that the existence of this problem forces producing regions to be ever more conscious about the necessity of proper farm management and meticulous processing in coffee production.

The specialty coffee community has started to become engaged in finding solutions for potato defect. In addition to a growing number of roasters supporting through purchasing, Cup of Excellence has started to organize the funding of potato defect research. Read more and support here.

- Melanie