Smoking is scenting by another source
The mechanism is the one the whole scenting family runs on. Dry or drying leaf is porous, low in moisture and enormous in internal surface area, and aromatic compounds in the surrounding air are absorbed into it. Placed beside opening jasmine blossoms the leaf takes up jasmine; placed in smoke it takes up the compounds smoke carries — principally the phenolic material produced when wood is burned or smouldered, which is what the nose reads as smoky, tarry, resinous or medicinal. Nothing has been added in the sense of a substance remaining in the packet, which is the same distinction the scented-against-flavoured page draws and which the ingredient list settles. That framing is useful because it tells a buyer what the variables are. Anything that changes what is in the smoke, how much of it reaches the leaf, how long the contact lasts and what the leaf was before it started will change the product, and those four axes account for essentially all the variation between one smoked tea and another. They are also all decisions a maker takes, which is why smoked tea rewards knowing who made it more than most categories.
The wood, and why pine is the reference
The traditional smoked tea of Tongmu in the Wuyi area is dried over smouldering pine, and pine gives the resinous, sappy, faintly sweet character that the style is known for. Different woods carry different phenolic profiles and produce recognisably different results, and producers outside the original tradition use what is locally available, which is one of the larger sources of variation between products sold under the same name. The condition of the wood matters as much as the species: resinous, freshly cut or damp material smoulders differently from seasoned wood and produces a heavier, more acrid smoke, while a clean slow smoulder gives a lighter and sweeter one. The temperature of the fire changes the balance too, since a hotter burn produces a different mixture of compounds from a cooler smoulder. None of this is usually stated on a packet. What a buyer can do is notice the character in the cup — whether the smoke reads as sweet and resinous or as sharp and ashy — and recognise it as information about the fire rather than about the leaf.
When the smoke is applied
The point in manufacture matters at least as much as the fuel. Smoke applied during withering acts on damp leaf with its cells still intact and its own processes running, and the aromatic material becomes part of the tea as it is made. Smoke applied during the final drying acts on nearly finished leaf and sits more on the surface. Some producers do both. The practical difference shows up across infusions: a tea smoked early carries its character through several steeps in step with the tea, while one smoked at the end front-loads and thins out, in the same way a surface-applied flavouring does. That is a check any drinker can run at home in ten minutes with a second and third infusion, and it distinguishes two products that the packaging generally describes identically. It is also why a heavily smoked tea can be either the most integrated thing in the cupboard or the most one-dimensional, and why judging the category on a single example is a poor idea — the range within it is wider than the range between many separate categories.
The base leaf, and the unsmoked original
The base matters and is rarely discussed, because the smoke is assumed to cover everything. It does not: a well-made base gives a smoked tea sweetness, body and a finish underneath the smoke, and a coarse one gives a cup that is smoke and very little else. The clearest demonstration of this is that the same production area makes an unsmoked version. Zheng Shan Xiao Zhong is the black tea of Tongmu and exists in both forms, and the unsmoked one is a delicate, sweet, longan-and-honey-inflected tea that most drinkers who know the smoked style have never tasted. Buying the two together is the single most informative purchase in this category, because it separates what the smoke is doing from what the tea is. It also reframes the smoked version: the smoke is a treatment applied to a specific fine black tea rather than a style in its own right, and the teas that borrow the style without borrowing the base are doing something different. A tea sold as smoked with no origin, no year and no mention of the base is a product rather than a description.
Where the name has travelled, and what else is in the market
A great deal of tea sold as Lapsang Souchong is made outside Tongmu, from other material, with heavier smoking, and some of it is smoke-flavoured rather than smoked. The last of these is a different production entirely — a flavouring preparation applied to finished leaf — and it is generally identifiable from the ingredient list and from the price. This is the standard shape of a famous-name substitution and the standard response applies: the substituted tea is often perfectly enjoyable, the loss is the difference between the price paid and the price the actual product commands, and buying the category rather than the name is the reliable move. Smoke appears in other places too. Russian Caravan is a blend style that frequently includes a smoked component and is a blend rather than a smoked tea. Some Chinese and Taiwanese producers use light smoking as one element among several. Certain Korean and Japanese roasted styles read as smoky without any smoke, because heavy roasting produces its own related compounds — which is a genuine confusion worth being able to tell apart in the cup.
Buying, storing and drinking one
Three practical notes. Smoked tea is among the most stable things in the cupboard, since the smoke character both dominates and persists, which makes it a good candidate for buying in quantity and a poor neighbour for anything else — it is the strongest aromatic source most households own, and a tin that has held it is a smoked-tea tin permanently. Brew it lighter than instinct suggests, because the smoke fraction comes out early and strongly and a first infusion can be almost entirely smoke with the tea underneath invisible; the second and third are where the base becomes legible, which is also where a good example separates from a poor one. And read a dislike of it precisely. Smoke is an assertive characteristic that a great many drinkers come to value after several encounters and that others never will, and it is exactly the sort of filterable fact the catalogue recommends recording: knowing that smoke is what you do not want saves years of money and is a different finding from deciding you dislike black tea.