I frequently use this section to rant endlessly about the sweet, juicy, and clean trifecta of great coffee but this week, we are going to talk defects. These are like the ‘garbage pail kids’ of coffee: easy to identity, unmistakable once you encounter them, and downright gross.

Fault One: Potato

Have you ever brewed a pot of Rwandan, Burundian, or Congolese coffee and rather than beautiful fruit flavours, you taste potato? It is the kind of potato flavour that I associate with off-brand potato chips that come in ‘plain’ rather than ‘regular’.  The cause of the stale, waxy flavour is the ‘potato bug’ defect. The notorious pest is a stinkbug of the genus antestiopsis (hemipteran, heteroptera, pentatomidae) often referred to as antestia bugs or variegated coffee bugs. Unbelievably, here is where it gets gross: these bugs have “a number of sacs or tubular outgrowths called crypts or cera” where a bacteria flourishes (Matsuura, et al: 2014).

While the bugs will eat stems and leaves, their favourite lunch is the coffee cherry. As the bugs feast, the enterobacteriaceae bacterium passes along a chemical: isopropyl-2-methoxyl-3-pyrazine (Matsuura, et al: 2014). Once brewed, pyrazine generates a harsh earthy flavour. Cause: yuck. Solution: if your cup tastes like potato stew, there is unfortunately nothing to do but dump it out. Maybe add some meat and carrots. While there are ongoing efforts to eliminate the green fault on the farm level, it remains daunting because the bacterial infection is invisible to the eye.

Fault Two: Cardboard

Cardboard flavours in the cup have two main culprits. The first is old green. After picking and processing, green starts a general decline in quality. Moisture slowly evaporates and flavours ‘flatten’ through a “loss of viability” (Selmar, et al: 2007). At a certain point in this downward spiral, the bean lose capacity to germinate and lipids oxidize, leaving the cup tasting like paper or wood. Next time you have one of those wee styrofoam cups of coffee – perhaps purchased at a gas station, university cafeteria, hospital, or rink – you will encounter this fault. At Cut, I aim for real short storage cycles (hence, our filter program emphasis on highly seasonal offerings and the ongoing farm shifts in the Cut Espresso blend).

The second cause of paper notes is a drop or spike in the bean temperature rate-of-rise (a measurement of changes in temperature over time). You will see this in coffees whose momentum can be difficult to control, for example a dense Kenyan offering, or in the handiwork of a careless or inexperienced roaster. Cause: dead green or roast error. Solution: add whiskey.

Fault Three: Hay, Bread, and Vegetables

Perhaps surprisingly, I would rather drink the potato defect – bacteria and all – than an undeveloped coffee. The most frequent cause of a ‘green’ tasting coffee is the inner bean. During roasting, the temperature differential between exterior and inner bean is key to producing a sweet cup. There is no shortage of roasters who charge (the temperature at which beans are dropped into the roaster) high and roast fast, usually resulting in a large of a variance in the bean and those ‘organic’ flavours of raw coffee: grass, wheat, hay, peas, etc. I like to crack open roasted beans to check for any gradations of colour (if you cannot crack a bean, it is certainly underdeveloped; if there are large degrees in shade, throw some). Cause: underdevelopment. Solution: send it back – it is not done yet.

Fault Four: “Roasty”

Do those quotation marks already reveal a dismissive attitude on my part? I have attended far too many cuppings and heard the term ‘roasty’ brandished like a scarlet letter. Roasty flavours are typically those associated with darker roasts. “Roasty” originates from a number of Malliard reaction derived flavour compounds, like alkylpyrazines that will give coffee a roasted nut flavour; or furfuryl, which instills a haze of burnt meat in the cup (Va Boekel: 2006). The progression of a roast leading to notes of toast, spice, ash, and char makes sense given that the longer sugar caramelizes the less sweet it tastes and Malliard reactions are very similar to the caramelization process.

Ultimately, I do not want any roasty notes in a cup but because the true benchmark for coffee should be sweetness (see past rants for rationale), I would gladly take sweet with a hint of roast than any sour or green. Cause: excessive development time Solution: drink it (if there is sweetness and a long, clean finish).


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