Extraction is several processes sharing a pot
A steeping leaf is doing at least three things at once. Water is soaking into dried, folded plant tissue and rehydrating it. Soluble material is dissolving off the wetted surfaces. And what has dissolved is diffusing out into the surrounding water. Each of those runs at its own speed, and each responds differently to heat, to leaf size and to movement in the pot. Treating steeping as a single process with a single dial — time — is why so much brewing advice fails when applied to an unfamiliar tea. The useful mental model is a sequence rather than a switch: the cup at ninety seconds is not a weaker version of the cup at three minutes, it is an earlier point on a curve where the proportions of what has come out are genuinely different.
What tends to come out early
Small, highly water-soluble molecules move fastest. In practice that means the amino acids that read as savoury sweetness, caffeine, and the lighter aromatic compounds are well represented in the first part of a steep. Larger polyphenols — the compounds most associated with astringency, and with the darkening and thickening of the liquor — continue coming out steadily after the fast fraction has largely finished. This is why a very short steep of a good green tea can taste sweet and thin at once: the sweetness arrived, and the body that would have carried it has not. It is also why extending a steep tends to add grip and colour rather than adding sweetness, and why a tea that was under-leafed cannot be rescued by leaving it longer.
Temperature changes the proportions, not just the pace
It would be convenient if temperature simply ran the same sequence faster, because then a long cool steep would reproduce a short hot one. It does not. The rate at which a compound dissolves and diffuses rises with temperature, but it does not rise by the same factor for every compound, so hot water does not merely arrive at the same destination sooner — it arrives somewhere else. Bitter and astringent fractions gain proportionally more from heat than the sweet and savoury fractions do. That single asymmetry is the mechanism behind nearly every temperature recommendation in tea: brewing a shaded green tea cool is not about being gentle, it is about selecting.
Why the second infusion behaves differently
The first steep spends part of its time wetting the leaf. By the second, the leaf is already open, already hydrated, and its surfaces are already in contact with water — so extraction starts immediately and runs faster from the outset. That is why a second steep at the first steep’s timing usually over-extracts, and why multi-infusion schedules so often go down before they go up. From the third or fourth infusion the leaf has less left to give and the times extend, sometimes steeply. Anyone whose second cup is reliably harsher than the first is watching this happen and can fix it in one move, by shortening rather than repeating.
The consequence for how you adjust
Because time, temperature and ratio act on the same sequence in different ways, changing two at once tells you nothing. If a cup is harsh, the first question is which sensation — a taste, or a drying grip — and the second is whether the water was hotter than the tea wanted. If it is thin, more leaf is almost always the right lever and more time almost always the wrong one. Adjust one variable, brew the same leaf again, and compare. This is slower than following a recipe and it is the only method that transfers to a tea nobody has written a recipe for.
Where this account is a simplification
Popular writing, including a good deal of it that sounds technical, presents crisp claims about exactly which compound leaves at exactly which second. Those numbers are usually generalised from a handful of laboratory studies on a few teas at a few temperatures, and they do not transfer cleanly to a rolled oolong opening over eight infusions or a compressed cake being boiled. What is well established is the direction: heat raises extraction rate for most soluble components, smaller particles extract faster than larger ones, and the fractions responsible for astringency continue coming out after the fast fraction has slowed. TeaHQ states those and declines to state a timetable.