Rock teas, from the Wuyi Mountains in China, are a separate category of oolong. This tea is known for its rich flavor and complex aroma signature between mineral, pyrogenic and floral, which is magnified by a long aftertaste (the flavors that remain after tasting). The most recent publications have focused on the impact of manufacturing (the steps involved in making tea) on the modification of aromas. More specifically, a number of studies have focused on the dynamics of the formation of non-volatile compounds (polyphenols, etc), volatile odorants that we detect during tasting, amino acids and sugars.
The manufacture of rock tea includes fine plucking of the leaves, wilting (dehydration), partial fermentation (alternating rotation and cooling steps), fixing (inactivation of enzymes in the leaf that modify the molecules), rolling, roasting.
Because of its gentle nature, the wilting phase of the leaves would release volatile molecules only to a limited extent but would modify the whole morphology of the leaf. If this is still not well known, this phase could modulate the flow of water and aromatic molecules. The partial fermentation allows a partial oxidation of catechins, explaining the presence of other molecules such as flavonoids. The roasting phase allows to "break" some molecules such as sugars and fatty acids allowing to form new aromatic molecules.
It is mainly the partial fermentation and roasting phases that impact the taste of rock tea. In a study on several fermentation and roasting stages (one to three) on Rou Gui rock tea, there are differences. The more the fermentation is repeated, the more molecules allowing a fruity/vegetal/flowery taste like jasmine/astringent are released. The more the roasting is repeated, the more molecules are released giving a sweet caramel/woody/opulent rose-like flower/nutty taste.
The duration of roasting would have an impact on the molecular aroma profile of Rou Gui tea. Low roasting forms a unique fruity, and grassy/fresh leafy taste with more astringency. Moderate roasting reduces the catechin content which reduces bitterness and astringency. It also brings toasted notes. Further roasting further reduces catechin and L-theanine content, which reduces the fresh, crisp taste but enhances woody, burnt/smoky, cinnamon, and opulent floral smells.
These recent works (2021 and 2022) bring new answers on the evolution of the aromatic profiles of rock teas according to different manufactures and are really interesting to identify and modulate the stages of the odor formation process. Some steps still need to be investigated, notably wilting and the impact of leaf morphology on the release of aromatic molecules.
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