Thank you for another great question! Acidity, sweetness, and bitterness are intuitive descriptors compared to terms like ‘clean’ or ‘flimsy’ or ‘syrupy’. Rather than articulating flavour, labels like ‘clean’ are qualitative descriptors for the texture, structure, and mouthfeel of a roast. Quick side note: not entirely sure what it is about the term ‘mouthfeel’ but saying it aloud makes me feel very gross.
In past dispatches, I have discussed how proper development is the foremost goal in my roasting because it ensures sweetness and, accordingly, best highlights an origin’s terroir. The result of proper development is the ability to ‘profile’ coffee by highlighting or eliminating ranges of taste notes (the volatile compounds that give sensory impressions). The crux of a clean coffee is in the articulation of flavours extending from proper development. Let us break down the roller coaster ride that I associate with clean coffee:
Part one is acidity. A coffee should open up with acidity that is not too aggressive or caustic. Think of the vibrant, lush acidity of biting into a ripe fruit or berry. The kind of mouthful that guarantees stains on your shirt and leaves you wishing you were eating over the sink. Counter to this is the tangy, jowl busting sourness of under-ripe fruit, pith, peel, and vinegar. It is usually too intense, too large, and too hazy. Rather than clean, I would call it muddy or soggy.
Part two is sweetness. A great coffee will move from acidity to sweetness seamlessly. With stewed and cooked fruit flavours replacing the bite of crisp acidity. From apple to pie, from berry to cobbler, from melon to jolly rancher, the sweetness should be deep and pair well with the acidity. If you never reach sweetness, the coffee is ‘flat’. For clean coffee look for refined notes of sweetness.
Finally, we have aftertaste. The mark of any good roast is a long, satisfying follow through. It will depend on origin, but I love a coffee that ends its journey with caramel and chocolate notes. A great cup lingers and a clean cup will leave with a smooth grace.
A clean coffee will articulate this journey well with precision in flavours. This does not mean simplicity beats complexity. It means that the complexity is pleasant and balanced. Rollercoaster was probably a bad comparison because I would say a coffee with angular, jagged twists or unpleasant combinations of flavours is not clean. Any cup that has a shadowy mess of opaque undisguisable notes is not clean. Moreover, any cup that is boring or flat is not clean.
tl;dr: clean describes a coffee that effortlessly balances crisp acidity to clear sweetness.