Water dissolves coffee’s solubles in a predictable sequence: bright organic acids first, then sugars, and finally the bitter melanoidins, tannins, and plant fibers. A cup’s taste character is largely a function of how far along this sequence the brew stopped. Stop early and acids dominate without sugars to round them out: underextracted coffee reads sour and salty. Push too far and the late-arriving compounds take over: overextracted coffee reads bitter, dry, and astringent. The desirable middle (roughly 18-22% of the grounds dissolved) captures the acids and sugars in balance with only a hint of bitterness (Barista Hustle).
This ordering is what lets a single number, extraction yield, stand in for taste on the Coffee Brewing Control Chart, and it is the mechanism the 4-6 Brewing Method exploits when its early pours steer the cup’s balance.