What is actually in the leaf
Carbohydrate in a tea leaf exists across a wide range of sizes. At the small end are the free sugars, present in modest quantities and mostly consumed or transformed during processing. In the middle are oligosaccharides and soluble polysaccharides. At the large end are the structural components of the cell wall — cellulose, hemicelluloses and the pectic substances — most of which are insoluble and stay in the leaf. What reaches the cup is the soluble fraction, which is a mixture rather than a single substance and which includes pectic material released as the leaf’s structure is broken down during processing and steeping. The catalogue gives no quantity for any of this, in keeping with the rule that runs through the whole sensory set: published values vary with cultivar, leaf maturity, season, processing and analytical method, and a single number would assert a precision nobody has. What is well established is the direction of the associations described below, and the direction is what is stated.
Why sweetness is not sugar
The free sugar level in tea is low enough that it cannot account for the sweetness a good tea shows, which is the fact that makes this page necessary. The sweetness comes from three other places: the soft sweetness of the free amino acid fraction on the tongue, the contrast effect by which reducing bitterness and astringency makes what remains read sweeter, and a substantial aromatic component arriving retronasally as honey, malt, caramel and dried fruit. What the carbohydrate fraction contributes instead is texture. This distinction is worth holding because it explains why sweetness in tea is so responsive to brewing — it is an emergent property of a balance rather than a quantity of one ingredient — and why a tea can read as sweet and thin at once, or thick and not particularly sweet. The two dimensions are separately caused and the catalogue carries them as separate sensory axes for that reason, with sweetness and body assigned independently by tasting rather than derived from any compositional claim.
What the polysaccharides are associated with
Viscosity and a coating quality — the sensation of a liquid that has body, that clings slightly to the mouth and that leaves an impression after swallowing rather than disappearing. This is a well-supported association in food chemistry generally, since dissolved polysaccharides raise the viscosity of a solution and change how it moves in the mouth, and it is the compositional half of the account of thickness. The perceptual half is more complicated and Sprint 31 sets it out: overall dissolved solids set a floor, proteins and larger peptides contribute, amino acids give a fullness that reads as roundness rather than viscosity, the larger oxidation products of a black tea behave partly as a colloidal fraction, fine suspended material contributes, and a liquor with strong retronasal presence is consistently rated as fuller than a comparable one without. So the polysaccharides are one contributor among several and not the explanation of body, which is exactly the sort of single-compound story this catalogue declines to tell.
What raises the soluble fraction
Three things, and the directions are well established even where the magnitudes are not. Leaf maturity: older and larger leaf and stem carry more of the structural material that these compounds come from, which is why mature-leaf teas such as shou mei and many hei cha give a thicker liquor than a bud-only tea from the same origin, and why the cheapest grade in a range is sometimes the fullest. Processing: extended withering, repeated rolling and bruising, and in dark tea the microbial phase all break down cell wall material and release more of it into solution. And time, since compression and ageing continue that work over years, which is a large part of why an aged sheng is described as thick where an equivalent young one is described as sharp. Together these explain a pattern that otherwise looks like a paradox: the categories with the finest plucking are frequently not the ones with the most body, and a drinker who has decided they prefer the cheapest grade in a range has usually decided they prefer texture.
The dark tea case, and where the microbes come in
Post-fermented tea is the category where this fraction is most obviously altered, because the microbial phase acts directly on the leaf’s structural carbohydrates. Wet piling in ripe pu-erh compresses that work into weeks under managed conditions; natural ageing in raw pu-erh runs it slowly over years alongside continuing oxidation; the deliberate fungal flowering of brick teas is a further variant. In each case a community of organisms is breaking down material that would otherwise have stayed in the leaf, and the thick, smooth, coating texture that dark tea is valued for is one of the outcomes. This is also why compressed dark tea rewards boiling water and long steeps that would ruin a partially oxidised tea, and why compressed cakes are frequently boiled rather than infused: the fraction being extracted comes out slowly and tolerates conditions that would over-extract a green tea long before. The catalogue records post-fermentation as a separate field from oxidation precisely because the two produce different compositions and therefore different textures.
The boundary of this page
Everything above concerns what is in the leaf and how it behaves in the cup: what dissolves, what it is associated with texturally, and what raises or lowers it in the finished tea. Tea polysaccharides appear in a separate literature concerned with quite different questions, and nothing on this page addresses that literature or anything it discusses — a compositional fact about a leaf and a claim about a physiological outcome are different kinds of statement requiring different support, and running them together is why so much writing about tea chemistry is simultaneously confident and unreliable. The claims made here are narrow and directional: soluble carbohydrate contributes to viscosity and to a coating sensation, mature leaf and stem carry more of the material it comes from, extended processing and microbial activity release more of it, and no single figure is given for any tea. Where a reader wants to reason further than that, the catalogue’s position is that the evidence for a texture claim and the evidence for anything else are not the same evidence.