Two routes to the same organ
Aromatic compounds reach the nose two ways. Orthonasally, when you sniff — air is drawn in through the nostrils carrying volatiles from the cup, the dry leaf or the empty vessel. Retronasally, when volatiles released in the warm mouth travel up behind the soft palate into the nasal cavity as you swallow and breathe out. The same compounds by either route, and the brain attributes the retronasal ones to the mouth, which is why they are experienced as taste rather than as smell. This is the mechanical reason that a tea tasted with the nose pinched has almost no flavour beyond bitterness and astringency, and it is the reason a cold makes tea taste of very little — the tongue is working normally and the larger channel is closed. The two routes do not deliver identical impressions even from the same liquid, which is why an experienced taster smells and then tastes rather than treating one as a preview of the other. The mouth warms the liquid, dilutes it with saliva and releases its volatiles gradually, so the retronasal impression is both later and differently proportioned than the orthonasal one. A tea that smells of one thing in the cup and reads as another in the mouth is not a contradiction; it is two samples of an unfolding process.
Why this changes how you should taste
Three practical consequences. First, smelling the dry leaf, the wet leaf and the empty cup is not a preliminary ritual — those are orthonasal samples of the same compound set the mouth will report retronasally, and each shows a different part of it. Second, breathing out gently through the nose after swallowing substantially increases what you perceive, which is why professional tasters slurp: aerating the liquid releases volatiles into the mouth’s air space where they can reach the nose. Third, a description that separates aroma from taste is more accurate and more useful than one that runs them together, because the two respond differently to brewing. Aromatics are largely lost to excessive heat and to time in storage; the tastes are not lost in the same way. A fourth consequence concerns the vessel. A narrow cup concentrates the air above the liquid and directs it towards the nose, a wide bowl disperses it, and a warm empty vessel holds the heavier compounds after the liquid has gone. This is not ceremony: the shape of the cup determines how much of the orthonasal signal reaches you, which is why aroma cups exist as a distinct object and why the same tea genuinely reads differently from a tasting set and from a mug.
What the orthonasal samples each tell you
The dry leaf gives the most volatile fraction, and it is the least representative of the cup — a flavoured tea in particular smells strongest here and weakest in the liquor. Warming a little leaf in a preheated empty vessel before adding water releases much more and is one of the most informative moments in a session. The wet leaf after the first infusion is the single richest source of information about a tea and is almost universally skipped: it shows aromatics that never make it into solution, it reveals processing faults, and it is where the distinction between a good and an ordinary example of a style is often most obvious. The empty cup after the liquor has gone holds the heavier, later-persisting compounds, which is why aroma cups exist as a separate vessel in some gongfu practice. There is a fourth sample that costs nothing and is almost never taken: the lid of a gaiwan or the underside of a teapot lid, lifted immediately after the infusion. Steam condenses there and carries a strong, concentrated aromatic signal, and lid-smelling is a standard part of gongfu practice for exactly that reason. Anyone with a lidded vessel already owns the equipment for it.
Why aroma is the fragile part
The compounds responsible are volatile by definition — that is what makes them smellable — and volatility means they leave. They leave during storage, which is why staleness reads first and most obviously as a loss of the top notes. They leave when water is too hot, driven off in the steam before they reach the drinker. They leave across infusions, which is why the first steep of a fragrant oolong is usually its most aromatic and the later ones trade aroma for body. And they are the part of a tea most easily lost in processing, which is why the aromatic categories are the ones where the maker’s skill is most visible. Almost everything in this catalogue about careful storage and moderate temperatures is, at bottom, about protecting the aromatic fraction. The same fragility explains why aroma is the dimension on which brewing errors are most expensive. A slightly over-extracted cup can be diluted and a slightly under-leafed one can be redone, but volatiles driven off in steam are gone from that session entirely. This is the argument for preheating a vessel and then letting water cool to the intended temperature rather than pouring boiling water onto a delicate leaf, and it is why the temperature recommendations for aromatic teas are as specific as they are.
Why aroma descriptions are so variable between people
Because they depend on the reference set a taster has. A note of sweet potato for a Dian Hong works for someone who eats Chinese sweet potato and works poorly for someone whose reference is a different variety. Notes of longan, of osmanthus, of yam or of cassia bark assume familiarity with those materials. Individual sensitivity varies too, and there are aromatic compounds that some people detect readily and others barely register, which is well documented for several classes of odorant. This is why TeaHQ describes conventional notes as commonly described rather than as facts about the liquid, why the catalogue keeps free-text notes alongside a coarse controlled vocabulary, and why an honest tasting note is a pointer to a resemblance rather than a claim about content. Familiarity also builds in one direction only. A taster who has smelled osmanthus will find osmanthus in a tea that has it; a taster who has not will register something floral and unplaceable. This means aroma vocabulary is acquired by encountering materials rather than by reading descriptions, which is why the most effective way to improve at tasting tea is often to smell things that are not tea — spices, dried fruit, herbs, wood — and give them names.
The limits of this account
This page describes the mechanics of how smell reaches the nose during drinking, because that is what changes how somebody tastes. It does not go further into the physiology, and it makes no claims about anything beyond the perception of the drink. Popular writing on tea frequently crosses from the mechanics of tasting into assertions about what compounds do once swallowed; that is a different subject, governed differently, and it is not this catalogue’s. What is stated here is uncontroversial sensory mechanics: two routes, the same organ, a large majority of what people call flavour arriving by the second route, and a set of practical tasting habits that follow directly from it. One further limitation is worth stating for completeness. Individual differences in what people detect are real and well documented for several classes of odorant, so two attentive tasters can disagree about a tea without either being careless. That is a reason to weight notes that recur across many independent descriptions and to hold single vivid ones lightly, and it is one of the arguments for the two-layer approach this catalogue takes to recording sensory data at all.