Every brewing decision selects a fraction
The compounds in a leaf do not all dissolve at the same rate or respond to heat by the same factor, so a brewing decision is a decision about which of them arrive and in what proportion. The amino acid fraction associated with umami and soft sweetness extracts readily even at low temperatures. The polyphenol fraction associated with astringency and bitterness gains proportionally more from heat and keeps arriving over time. Caffeine extracts quickly and early. The volatile aromatics are released early and are driven off by steam if the water is too hot. Larger structural material contributing to body comes out more slowly and rises with dose. Because these five behave differently, no single dial makes a cup simply stronger — every adjustment changes the balance, which is why the same leaf can honestly be described in several incompatible ways. This is also the reason the catalogue records brewing parameters alongside every sensory judgement it makes, and why it regards a tasting note without a ratio, a temperature and a time as an anecdote rather than a description.
Temperature, and what it does to the note
The single strongest lever on which descriptors appear. Cooler water selects the sweet savoury fraction and leaves much of the bitter and astringent one behind, which is why a shaded Japanese tea brewed cool reads as sweet, brothy and thick, and why the same leaf at black tea temperature reads bitter and thin. Cooler water also releases fewer volatiles, so a very cool brew can under-report the aroma the tea was made for — which is the specific reason a technically correct low-temperature gyokuro sometimes disappoints, and why many drinkers run a cool first infusion and a warmer second to sample the tea twice. Hotter water brings out aroma at first and then drives it off in the steam, extracts more of everything including the material that carries body, and moves the balance towards grip. In descriptor terms: cool gives umami, sweet, thick, marine; hot gives aromatic, brisk, astringent, and eventually bitter and flat at once. The same leaf, two vocabularies, and neither description is wrong.
Ratio against time, which are not interchangeable
The commonest brewing misconception is that more leaf and more time do the same thing. They do not. A higher leaf-to-water ratio raises everything roughly in proportion, so it increases body and intensity without shifting the balance much, and it is the most reliable way to make a thin cup fuller. A longer steep shifts the balance, because the fast sweet aromatic fraction has largely finished while the astringent late fraction keeps arriving, so extending the time makes a cup grippier rather than merely stronger. In descriptor terms, a higher ratio moves a note towards full-bodied, rich and intense; a longer steep moves it towards drying, astringent and eventually flat. This is why the high-leaf, short-steep approach of the gongfu styles produces such a different set of notes from a western mug at the same apparent strength, and it is why a tea that has gone grippy cannot be rescued by dilution — adding water produces a weaker version of the same imbalance rather than the cup that a shorter steep would have given.
Infusion number, which changes the tea more than most variables
A multi-infusion session is a sequence of different teas made from one leaf, and treating a description of the first as a description of the tea is a common and expensive error. The first infusion is the most aromatic and the most bitter, since the volatile fraction and the caffeine both arrive early. The second and third are usually sweeter, thicker and less bitter, and are where a good tea shows its structure. Later infusions trade aroma for body, and many teas show their longest finish in the second or third rather than the first. A roasted tea in particular reads as almost entirely roast on the opening steep with the base invisible, and only becomes legible from the second onwards — which is why judging a heavily roasted oolong on one cup is judging the firing. The practical instruction is to write a note per infusion rather than a note per tea, and the diagnostic use is that a tea whose finish shortens abruptly is nearly exhausted, which is a better signal to stop than colour or a count of steeps.
The variables nobody records
Three that move descriptors and rarely appear in a note. Agitation: stirring, squeezing a bag, shaking an infuser or pouring turbulently all increase extraction of the astringent fraction, so the same bag squeezed and unsqueezed produces noticeably different cups. Filtering: a liquor carries fine suspended material as well as dissolved material, so the same tea through a paper filter and through a coarse strainer produces two textures, and a cup poured through a very fine filter reads thinner. Vessel: a narrow cup concentrates the air above the liquid and directs it at the nose while a wide bowl disperses it, unglazed clay holds aroma and is dedicated to a category for that reason, and a lid changes what is retained. Any of these can account for a difference between two people’s notes on the same leaf, and none of them is usually written down. Recording them costs nothing and converts an unreproducible impression into something that can be repeated or argued with.
The practical upshot for reading and writing notes
When reading a description, ask what preparation produced it, and read a listing with no parameters as describing the seller’s house method rather than the tea. When a description does not match your cup, suspect the parameters before the tea, and reproduce their method once before concluding anything — this is the most frequent cause of a mismatch and the easiest to test. When writing, record the parameters as a matter of routine, and where a tea is genuinely versatile, record two sets rather than picking one. And when a tea disappoints, change one variable at a time: temperature first for bitterness, time and grade and agitation for astringency, ratio for thinness. Changing several at once is why so many people cannot work out what fixed their tea. All of this is the same single-variable discipline the comparison pages recommend, applied to a single cup rather than to a flight, and it is the difference between accumulating knowledge and accumulating opinions.