Leave coffee brewing too long and it does not simply become more of itself. It becomes a different drink, one with flavours in it that were not present in the good version at all. That is the fact most brewing advice skips, and it is the reason "too strong" and "over-extracted" are not the same complaint.
Water pulls compounds out of coffee grounds in a rough order, easiest first. Acids and the light aromatic compounds come early, sugars and body-building compounds in the middle, and bitter, drying, woody compounds last. Stopping early gives you a sour, thin cup. Going long gives you a harsh, hollow one. The good coffee is a window in between, and every brewing variable you touch is really moving you along that ladder.
Strength and extraction are two different dials
This is the distinction that unlocks everything else, and the vocabulary exists for it.
Strength is how much dissolved coffee is in the water. Professionals measure it as total dissolved solids. A strong cup has more coffee material in it than a weak one, and that is all strength means.
Extraction is what proportion of the coffee you started with actually made it into the cup. It is a percentage of the dose, not a concentration in the water.
You can have all four combinations, and they taste different. A strong, under-extracted coffee is intense and sour at once. A weak, over-extracted coffee is thin and bitter at once. Easto cites a finding that fits everyday experience precisely: the highest perceived sourness showed up in a brew with high dissolved solids and low extraction, the lowest pH of the set, while the cup that seemed to lack acidity had low solids and high extraction.
So when a coffee tastes wrong, "make it stronger" is not a diagnosis. The question is which of the two dials moved.
What comes out, roughly in order
Treat this as a useful approximation rather than a chemical schedule. The compounds overlap, and the order is a tendency, not a queue.
Early: acids and volatile aromatics. These dissolve readily and they leave the grounds first. They carry most of what people describe as brightness, fruit and florality. Citric acid tends to read as a burst of tartness, malic as a smoother tartness, and acetic and formic acids are thought to contribute a winey character. Stop the brew here and you get the sour, sharp, slightly hollow cup that is the classic under-extraction signature.
Middle: sugars and the compounds that build sweetness and body. This is where a cup gains its middle. Sweetness in coffee is mostly perceived rather than measured as sugar content, and it is what balances the acids that arrived first. Most of what you want lives in this band.
Late: bitter compounds and drying ones. Compounds derived from chlorogenic acids, including caffeic and quinic acids, arrive here, along with the phenolic material that produces astringency. Astringency is worth separating out because it is not a taste at all. It is a tactile sensation, the drying, mouth-puckering feel, and it comes from compounds binding to proteins in your saliva. That is the "woody" quality in an over-brewed cup: partly bitterness, partly the sensation of your mouth drying out.
Never fully: the insolubles. Some material does not dissolve at all. Polysaccharides such as cellulose, hemicellulose, arabinogalactan and pectin are too large to go into solution, so they uncoil and stay suspended. Larger particles you can actually see are fines, or sediment once they settle. These matter more than their size suggests, because insoluble solids including lipids are largely responsible for aftertaste, which is why the flavour that lingers after you swallow is often nutty, cocoa-like or roasted rather than fruity. Soluble compounds get washed away in the swallow. The insoluble ones stay behind and keep talking.
That last point explains something people notice and cannot name: why a paper-filtered coffee and a press coffee from the same beans have different endings, not just different bodies.
What this changes about fixing a bad cup
Once the ladder is in your head, the diagnosis becomes a single question: did the brew stop too early or run too long?
Sour, sharp, thin, disappears quickly. You stopped early. Grind finer, brew longer, use hotter water, or stir. All four move you up the ladder.
Bitter, harsh, drying, hollow in the middle. You ran long. Grind coarser, shorten the brew, ease off the temperature.
Notice that "add more coffee" appears in neither list. Adding coffee changes strength, not extraction. If the cup was harsh, a stronger version of it is a harsher version of it. This is the single most common mis-fix in home brewing and the ladder is what prevents it.
The corollary is the one worth carrying to the shelf: grind size and contact time are two ends of the same lever. A thirty-second espresso needs a fine grind because it has almost no time. A four-minute press needs a coarse one because it has plenty. Method-specific grind charts stop looking arbitrary the moment you see they are all solving the same equation.
What this will not do
The ladder will not tell you the right answer, only the direction. There is no universal target percentage that makes a coffee good, and two coffees at identical extraction can taste completely different, because the compounds available to extract differ by origin, process and roast. Sensory evaluation still needs a person.
It also will not rescue a bad grind. If your grinder produces dust and boulders at the same time, the dust over-extracts and the boulders barely extract, and both are happening in the same cup. No adjustment to time or temperature fixes that, because you are not moving along one ladder, you are on two at once. That is a hardware problem and honesty demands saying so.
And it does not apply cleanly to espresso, where pressure, an enormous amount of surface area and a very short contact time make the picture more complicated than a filter brew.
The one experiment worth doing
Brew the same coffee three times at the same dose and grind, and change only the contact time. Short, normal, long. Taste them together rather than one after the other on separate mornings.
You will taste the sour end and the drying end as distinct failures rather than as vague wrongness, and after that you will never again respond to a bad cup by adding a spoonful. That is worth twenty minutes.