There’s nothing quite like waking up to a fresh brewed mug wafting with the aroma of… raw potato. Now, few of us would run the other direction when faced with a diced Russet, but in your coffee cup? You might euphemistically call such a scent ‘unique’ the first time you encounter it but for the most part, it’s gross.
This “potato taste,” caused by a toxin-creating bacteria eating a hole in the cellular walls of the coffee cherry, is not only a bizarre addition to the flavor profiles found in coffees from the Great Lakes region of Africa (Rwanda, Burundi, Tanzania) but it might just be the downfall of Rwanda’s entire specialty coffee industry. One bad bean can ruin an entire batch, even one otherwise considered the cream of the crop. I flung open the door of the cupping laboratory the other morning to find three cuppers hovered over nine glass cups, frowning. Leticia hands me a stainless spoon, wide brimmed with a steep handle, made specially for coffee cupping. “Taste that,” she points with her chin to the cup on the right. I take a slurp from the spoon. It’s tepid, acidic, and vegetal. I nearly gag.
It’s been a consistent routine with my friends over in Kigali’s coffee cupping laboratory that they have me taste the defects. I suppose they consider it instructive, although when the first sip of a coffee you have at 8am lingers with asparagus and potato, well, you might start craving a vanilla-mocha frappuccino. This particular round of samples was destined for Intelligentsia Coffee, based in Chicago and Los Angeles, but Intelligentsia would not be shipped one of their three coffees until further sorting and cupping determined the lot to be potato-free.
While there are pesticides that combat the potato taste-causing bacteria at the root of the problem on the plant itself, distributing pesticides to Rwanda’s thousands of coffee farmers is not the method chosen by the country thus far to prevent potato contamination. Rather, plentiful and cheap labor means over 300 women, and the occasional man, are employed full-time in Kigali’s coffee warehouses sorting out the defective beans from piles on the ground. The country’s fully-washed high-grade coffees, those that have undergone the most sophisticated type of processing from cherry to bean (about 3,000 tons of Rwanda’s total annual production of 40,000 tons), have already been picked over up to three times at the washing station for cherry that is under-ripe, over-ripe, or split open by bacteria. So understandably there is some frustration on the part of the cuppers when they roast samples that emanate aromas of raw potato, or when the often-subtle but unmistakable potato flavor coats their tongues. It’s a problem keeping the specialty coffee industry here on its toes, and creating sorting jobs for those who might otherwise have few employment options.
Misplaced vegetables aside, the cuppers have introduced me to a plethora of aromas and flavors in our mornings’ sampled coffees that have been challenging to detect and also brilliant when identified. During one round this week, a selection of samples from the Kayumbu washing station, found in Gitarama province just west of Kigali, was separated not only by the day of harvest but also by sorted grade: a single day’s harvest separated into grade A and grade B. Over 100 farmers might have contributed to any given day’s harvest making it impossible to identify the location of the coffee beyond the washing station, presuming that the cherry was grown within a ten-kilometer radius or so. Cherry ripening occurs later at higher altitudes; the higher the contrast between daytime and nighttime temperature (as occurs at higher altitudes), the more concentrated the sugars of the coffee plant become and thus produce, at least in theory, more flavor development. Harvesting cherry later in the season also presumes the sugars have had more time to develop, but as with all stages of coffee processing, a few under-ripe or diseased beans could throw off an otherwise fully-ripened, late-harvest batch.
I’ve learned the protocol for cupping well enough to know that when slurping from the spoon, you must do it loudly. Still though, I’m repeatedly corrected on my poor technique of breaking the crust of the grounds, which allows the aromas to escape. Properly, it involves a circular motion of the spoon reminiscent of the elegantly deliberate way a Japanese tea master cleans his utensils. My way, it involves pushing some of the grounds aside furtively with the back of a spoon and leaning in close enough for the steam to burn my nose. Before the crust of the grounds is broken, the cups look murky enough to be holding a foamy Guinness, or maybe brownie batter. The foam is spooned off after four minutes, un-precisely, and the brew cools down to warm before the cuppers slurp their spoonfuls. Flavors change somewhat dramatically as coffee cools and the hotter it is the more imperfections can be masked. This is a reasonable excuse for the bottomless coffee cup served at diners, which are always in need of hot refreshment.
But in the cupping lab, all of coffee’s possible imperfections must be unveiled. In today’s line of two dozen samples (with three cups of each sample brewed to taste for consistency), I cup a Kayumbu harvested on May 30th that tastes harsh and tangy on my tongue, lingering like lemon pith. Another Kayumbu from June 9th is chalky and watery, full of tannin and lacking in body… but this I only perceive when I slurp a spoonful of a Kayumbu from May 22nd that is by comparison full-bodied and tastes wholly like, well, coffee.
I wonder, though, after a personal revelation that the variation in coffee samples are perceptible only through extensive side-by-side tasting, if taste is ever absolute. A recent article in Gourmet magazine reported on this topic, explaining how flavor chemists are disproving years of scientific theory that understood the four basic ‘tastes,’ sweet, bitter, salty, and sour, perceived reliably on each individual’s tongue in the same place. This is the flavor equivalent of every human seeing the ocean as the same shade of blue, but the most recent theory in flavor chemistry? It’s that everyone tastes differently. Your shade of blue is not my shade of blue. In the specialty coffee industry, where three cuppers’ scoring a coffee sample above 88, let’s say, translates into a dollar more per pound than that coffee would get if it scored an 82 (or at least this gets the attention of buyers who are willing to pay more per pound), this new understanding of flavor means money. My observation of the cuppers thus far is that they all score samples reliably close to one another. While Leticia might give a sample her highest score of the day at 87, Claire might give the same coffee an 88. In other words, they’re all perceiving samples within the same ranges.
Even more interesting, this Gourmet article touched on the fact that taste might fall along cultural lines, with certain cultural groups tasting things differently from others. Now anyone who has traveled beyond Western Europe would nod in agreement, but how do you teach someone to taste the “heavy body, citric, honey and phosphorus in the mouth,” as Uzziel did while cupping a coffee from the Lake Kivu region of Kibuye? He scored this particular sample an 88, by the way, solid but short of exceptionnel.