Oolong's Astringency Peaks Lower Than Green Tea's, a Study Finds
Researchers at Hunan Agricultural University tracked astringency second by second in six teas and reported oolong's builds slower than green tea's, alternating between "rough" and "dry.
Oolong's astringency builds more slowly and peaks lower than green tea's, and arrives as two alternating sensations, rough and dry, a study of six teas reported June 24.
A team at Hunan Agricultural University set the finding down in Food Chemistry X. The researchers tracked astringency as it rose and faded over each sip, rather than scoring it once, and tied the differences between green, black, and oolong tea to how far each leaf had been oxidized.
Astringency is the drying, puckering feel a tea leaves in the mouth, a tactile sensation rather than a taste. The team measured it four ways: a time-intensity panel, which rates how strong the sensation is from moment to moment; a temporal dominance of sensations panel, in which tasters mark which sensation is dominant at each instant; an electronic tongue, a sensor array that reads the liquor; and LC-MS, an analytical method that separates and identifies the compounds present.
Green tea's astringency reached a higher peak, added up to more over the whole sip, lasted longer, and set in faster than oolong's or black tea's, the study said.
The character differed too. In the dominance panels, green tea was ruled by "harsh" and "coarse grain," black tea by "smooth" and "dry," and oolong alternated between "rough" and "dry," the researchers said.
The chemistry matched the sensation. LC-MS linked stronger astringency to anthocyanins, quercetin derivatives, and catechin oxidation products, the study said. Roughness tracked with polymerized catechins, a grainy quality with flavanols, and dryness with oxidized polyphenols. The type and structure of the polyphenols, not only their quantity, set the feel.
Oolong sits between green and black tea because it is only partly oxidized. Black tea carries that same enzymatic reaction to completion, and earlier tea-chemistry work has traced what follows: catechins polymerize into the larger theaflavin and thearubigin pigments, and the cup reads less sharply astringent as a result. The new study adds a second axis to that record: oxidation changes the kind of astringency as well as its strength.
For a drinker working through a gaiwan, the result names what the tongue already registers: the rough edge of an early infusion, the dry finish behind it. The study compared six finished teas, not brewing variables, and its authors noted that the dynamic patterns of astringency across tea types remain underexplored.
Sources: Food Chemistry X, A study on the dynamic differences and component correlations of astringency in green tea, black tea and oolong tea based on TI/TDS and LC-MS; Journal of Food Science, Phytochemical profile of differently processed tea: A review; Molecules, Enzymatic Oxidation of Tea Catechins and Its Mechanism.