Farm Wars - Episode 5:The Potato Strikes Back

 

Being an avid appreciator of all things breakfast food, especially those which involve a gravy, it is quite often I who mashes the potato. However with the early test roast of our Gitwe Natural Long Miles auction lot and its subsequent refunding occurring not too long after. It is me, sitting in a cafe on my 5th cup of coffee and my 5th minute of sleep, that has been mashed by the potato. Slightly more succinctly, mashed by a coffee bean masquerading as a potato for what I can only assume is in preparation for Halloween which is soon to be upon us. Even more succinctly, the infamous Potato Taste Defect [PTD].

Now problems like these are sort of unavoidable when dealing with a seasonal agricultural product so we thought, why not use this incident as an educational opportunity. After all, our fists are better utilized shaking a masher into a bowl of boiled potatoes than at the sky. With the necessary preamble out of the let us now get into what exactly happened with our auction lot.

What is PTD?

Potato taste defect is a coffee defect most commonly encountered in the Great Lakes region of Central and East Africa, particularly Rwanda, Burundi, the Democratic Republic of the Congo and Uganda, and less frequently in Tanzania and Kenya.As the name suggests, the telltale sign is the smell of freshly peeled potatoes when the affected coffee is ground. 

PTD has historically been associated with damage caused by the Antestia bug, an insect that feeds on coffee cherries while they are still developing on the tree. The insect's feeding activity can damage the fruit and potentially provide an entry point for microorganisms that contribute to the defect. Research has implicated bacteria, including Pantoea species, in the production of the compounds responsible for the characteristic aroma. This aroma is caused by the compounds 3-isopropyl-2-methoxypyrazine (IPMP) and 2-isobutyl-3-methoxypyrazine (IBMP). IPMP, in particular, is strongly associated with the characteristic potato-like smell. These methoxypyrazines are extraordinarily potent aroma compounds, meaning that even tiny concentrations can have a substantial sensory impact. Research has also found that PTD-affected beans exhibit changes in their broader volatile-compound profiles, so the defect is not necessarily explained by one molecule acting in isolation.

There are competing explanations for how these compounds come to be present. One hypothesis is that bacteria introduced through insect damage produce them. Another is that damage and stress trigger biochemical responses in the coffee plant itself, allowing it to produce methoxypyrazines through its own metabolic pathways. Recent experimental work published in the 2025 edition of the international journal of fruit science has also suggested that mechanical damage to cherries can contribute to PTD independently of Antestia bug infestation though its rates are not as high as those seen in infestations.

We don't yet have a complete picture of how these pathways interact, when exactly the compounds form, or which factors determine whether an individual bean develops the defect. What we do know is that the chemistry starts before the coffee reaches the mill, and that the resulting compounds can persist through subsequent processing.

How does PTD slip through quality control?

PTD is generally sporadic and is generally confined to the individual bean it has developed in and is not contagious. It is generally quite rare occurring in about 1 bean in 3.3 lbs of coffee though that is an average and acute cases may show quite a bit more variance. It is however quite potent and even 1 PTD affected bean in a dose may make it taste quite heavily of raw potato. It's entirely safe to consume but it's quite unpleasant and more importantly, will necessitate a thorough cleaning of  your grinder after grinding a dose as the flavor may show up in your following brews, a hassle we would really rather not put our customers through.

Given the meticulous care put into processing this auction lot and the fact that the defect rate is quite low to begin with. We didn't find any PTD beans in our first few QC brews of the coffee and thus approved it for shipping. In subsequent brews, however, we encountered a very potato-forward brew. After more investigation and brewing, we noticed that a bag of the Gitwe may have even more than 1 defective bean per bag. We could argue that most bags will probably be fine, and statistically, that may well be true. But a quality benchmark is only meaningful if we apply it when doing so is inconvenient.

What can be done to prevent PTD?

As with most agricultural problems, prevention starts on the farm. The Antestia bug is one of the primary factors associated with PTD, and managing its presence is an important part of reducing the risk. Removing residual cherries left over from previous harvests is a good general practice, helping limit pest populations while also reducing pressure from coffee berry borers. Chrysanthemum-derived concentrates can also be useful as botanical pest deterrents when applied appropriately. These are relatively straightforward interventions, but their effectiveness depends on the resources available to farmers and the conditions they are working with.

Unfortunately, PTD is not quite as simple as identifying a pest and getting rid of it. We still have a limited understanding of the biochemical pathways responsible for the defect, and emerging research suggests that mechanical damage to cherries may also play a role. This means that even with diligent pest management, careful harvesting and good agricultural practices, there is no guarantee that a crop will be entirely free of PTD.

Better sorting and quality control can help, like in Rwanda where UV lights are used to help assist with sorting out such defects. But these are not complete answers either. PTD can be concentrated in individual beans, and an affected bean does not necessarily look different enough from a healthy one to be identified through visual inspection alone. This makes the defect particularly difficult to manage further down the supply chain, where the available interventions become increasingly limited.

Ultimately, reducing PTD requires a combination of improved farm management, better detection methods, continued research and, importantly, the financial means to implement these measures. Better infrastructure, more effective pest management, improved harvesting and handling facilities, and investment in research all cost money. These are not things that can simply be demanded of producers without considering whether they have the resources to put them into practice.

If we want fewer defects, better consistency and more opportunities for exceptional coffees from these origins to reach the market, we need to help create the conditions in which producers can continue improving their work. That means purchasing good coffee at prices that recognise the work involved, providing a degree of security in the market, and supporting systems that make further investment possible. Prevention is a shared interest, and it should be treated as such.

How does processing interact with PTD?

Processing is an interesting part of the PTD puzzle, largely because it is an area where we have some promising theories but very few definitive answers.

The chemical precursors associated with potato taste defect develop while the cherries are still on the tree. The exact mechanisms remain incompletely understood, but insect damage, mechanical injury and the microorganisms associated with them appear to be important factors. By the time the cherries reach a processing facility, at least some of the chemistry responsible for the defect may already be established.

This makes PTD particularly difficult to resolve through conventional processing. Washing, fermentation and drying can dramatically alter the flavour profile of coffee, but that does not mean they will reliably remove every undesirable compound. The key odorant, IPMP (3-isopropyl-2-methoxypyrazine), is extraordinarily potent, and the pathways through which methoxypyrazines are degraded are not well established. There are theories that inoculating coffee with selected microorganisms during fermentation could help outcompete undesirable bacteria, potentially hindering the defect from developing. Yeasts can metabolise various compounds and significantly alter the flavour profile of coffee, but there is currently insufficient evidence that they can reliably break down the specific compounds responsible for PTD.

Establishing whether this is possible would require deliberate experiments, measuring the relevant compounds before and after fermentation and checking that any intervention does not introduce other unwanted flavours. It would also be necessary to distinguish between preventing the defect from developing and removing compounds that are already present. These are two very different problems.

It might be particularly fruitful to conduct research rooted [i am not sorry] in investigating the processing of cherries or beans known to be affected by PTD, rather than relying exclusively on sensory observations of finished lots. For now, careful handling, appropriate farm management and effective quality control remain the most practical tools available.

How does CETO interact with PTD?

Given our no-questions-asked refund policy, you can probably gather that we hold ourselves to a particular quality benchmark. We are not interested in asking customers to make excuses for a coffee that does not meet it, and the Gitwe situation warrants an automatic refund. While most bags will probably be fine, we would rather not take that chance on your behalf. As for what you can do with this bag, unless you’re particularly keen on indulging in the opulent display of excess which is throwing it in the trash. You could use it to lighten the *joys* of seasoning those new burrs you just got since you’ll need to clean them afterwards anyways. Composting the coffee is also a perfectly reasonable option and one we’d generally recommend. What we would not recommend however is serving these at the family dinner as a time efficient substitute for mashed potatoes. Though there may still be a culinary application for it out there in the world of maddened mixology in case you wanted to distill a certain rustic or should i say, russet charm to your questionable concoctions.  

We will be more diligent about looking out for these sorts of issues in the future but we will however not really grow apprehensive about purchasing coffees from these origins. They are among the world's most dynamic coffees with very interesting profiles and are personally some of my favorite origins. We believe the producers behind them deserve access to markets that value their quality and the care they put into producing them. We ourselves look forward to directly supporting these producers by bidding in upcoming auctions like the upcoming Best Of Rwanda 2026 auction so that producers from these origins may obtain the financial resources to help mitigate problems like these.

We of course have no intention of pushing any risks relating to that decision [though there is realistically very little risk] onto our customers. We will be more diligent about looking out for any problems like this since it's a risk you encounter when dealing with agricultural products and we are more than happy to grapple with it.

How does this affect farmers?

There is another side to this conversation that we think deserves attention. A defect like PTD does not exist in isolation from the people producing the coffee, and the way the industry responds to it can have consequences that extend well beyond an individual bag.

Coffee production is an agricultural undertaking, not a factory process in which every variable can be controlled. Farmers make decisions months, sometimes years, before a coffee reaches a roaster's cupping table. They invest labour, land, equipment and money into a crop without knowing exactly what the weather, pests or other biological variables will bring. Even with careful farming and processing, there will inevitably be occasions when something goes wrong.

When that happens, it is worth asking who is best positioned to absorb the resulting risk. Farmers already contend with considerable uncertainty in production, and they often have far less financial flexibility than the buyers further along the supply chain. Expecting them to absorb every loss, including those arising from defects that may be impossible to prevent entirely, can make an already difficult business considerably more precarious. A business that we already see more farmers leave year over year, switching to more secure and profitable pursuits, be it in cultivating different crops or leaving farming altogether.

Why will be buying even more from these origins

We have no intention of becoming apprehensive about purchasing coffees from these Origins. In fact we plan to do quite the opposite.These origins produce some of the most dynamic coffees in the world. They offer an extraordinary range of flavour profiles, from remarkably clean, delicate and tea-like cups to intensely expressive, fruit-forward coffees that would make most juice yearning brewers blush, all for prices we tend to take for granted. The producers working in these regions have developed an enormous amount of skill, and the coffees they produce deserve to be judged on their quality rather than reduced to the occasional agricultural defect associated with their origins.

These are also some of our personal favourite origins. We want to keep buying from them, discovering new producers and bringing these coffees to customers who might otherwise never have the opportunity to experience them. A problem like PTD is MORE reason to continue supporting origins like these.

We intend to continue supporting producers directly through bidding in auctions organised for/by farms including the upcoming Best of Rwanda 2026 auction. Auctions can create opportunities for exceptional lots to receive greater recognition and command prices that reflect their quality. They also connect producers with buyers who are willing to seek out distinctive coffees and invest in the work behind them more directly, cutting out a lot of middlemen and establishing a more direct cashflow source to the farmers.

That investment matters beyond the immediate value of an individual lot. A market willing to pay for differentiated, carefully produced coffee gives producers more financial room to invest in better sorting facilities, improved processing infrastructure, effective pest management, more careful harvesting and further experimentation. These improvements can help reduce the likelihood of defects, improve consistency and support continued progress in quality. They cannot guarantee that PTD will disappear, but they can strengthen the resources available to manage problems like it.

Of course, purchasing a coffee at auction does not, by itself, solve the structural challenges facing producers. Nor can we pretend that buying exceptional lots is a substitute for better agricultural research or broader investment in producing regions. But direct purchasing and participation in these markets are tangible ways for us to support producers whose work we believe deserves recognition, while helping sustain the economic incentives that make continued investment possible.

That said, thank you for supporting us through little hiccups like these. We wouldn't be here without you, and we are grateful that you trust us to handle them properly. We will keep learning, refining our quality control and bringing you interesting coffees from producers and origins we believe in. Most importantly, we will continue to stand behind the quality we promise without losing sight of the people who make it possible. That will be all for now!