Decoding flavour: acidity, sweetness, body

Most tasting notes describe fruit. Peach, blackcurrant, tangerine. They are useful shorthand, but they are the last layer, not the first. Underneath them your palate is doing something much simpler: measuring three things at once. How bright the coffee is, how sweet it is, and how heavy it feels. Acidity, sweetness, body. Learn to separate those three and every tasting note you read afterwards makes more sense.

Acidity is not sourness

Acidity is the sensation of brightness: the lift at the front of a sip, the thing that makes coffee taste alive rather than flat. In a green coffee it comes mostly from organic acids formed in the fruit and during processing. Citric and malic acid dominate the pleasant end of the spectrum — citric reads as lemon, lime, grapefruit; malic as green apple, pear, sometimes stone fruit. Chlorogenic acids are present in much larger quantities but taste more of astringency and dryness than of fruit. Roasting degrades these acids in a fairly predictable order. Citric and malic acid fall away steadily with time and heat, which is why a light roast tastes sharper and a darker one rounder. Chlorogenic acids break down into quinic and caffeic acid, and quinic acid is a large part of why very dark or very stale coffee tastes hollow and drying rather than bright. Sourness, as opposed to acidity, is usually not the bean's fault at all: it is under-extraction, and we come back to it below.

Sweetness is built, not added

A ripe coffee cherry holds sucrose in the seed, and how much of it survives to your cup decides most of what you like about a coffee. Slow ripening at altitude, and careful picking of ripe fruit only, put more sugar in the seed to begin with. Roasting then spends it. Some sucrose caramelises into the compounds we recognise as caramel, toffee and honey; some is consumed in Maillard reactions with amino acids, producing hundreds of aromatic molecules and, eventually, melanoidins — the large brown polymers that give roasted coffee its colour, much of its perceived body and a good deal of its bittersweet depth. The practical consequence is that sweetness is a narrow window. Roast too fast and the sugars never develop; roast too far and they burn into ash and dry bitterness. Everything we do in the roastery is aimed at that window rather than at a colour.

Body is physical

Body is texture, not taste: how much the liquid coats the tongue. It comes from lipids from the seed, soluble polysaccharides from broken-down cell walls, melanoidins, and suspended fine particles held in a colloid. Filter paper traps most of the oils and fines, which is why a V60 tastes clean and tea-like; a metal filter or a French press lets them through and feels rounder and heavier. Espresso concentrates all of it, plus an emulsion of oil and gas, which is why 30 g of espresso feels like more coffee than 250 g of filter.

Tasting it at home

• Brew two coffees the same way, side by side — ideally a washed African and a natural or honey from Latin America. Comparison teaches faster than description.
• Taste them hot, then again at room temperature. Acidity softens as it cools, sweetness and defects become obvious. Bad coffee tastes worst cold.
• Take one sip and ask only: bright or flat? The next: sweet or dry? The next: light or heavy? One question at a time.
• Slurp, loudly. It sprays the coffee across the palate and pushes aroma up into the nose, where most of what you call flavour actually happens.
• Write three words down. Not clever ones — bright, sweet, thin is a perfectly good note, and next week you will know what you meant.

Sour and bitter are usually brewing faults, not origin characteristics: sour means under-extracted, harsh bitterness means over-extracted. Fix the grind before you blame the coffee.