· Scientific articles · 3 minutes
The influence of roasting on rock tea
Rock oolongs from the Wuyi Mountains are very popular among tea enthusiasts, due to their intense, well-rounded aroma, which largely comes from the roasting process, often carried out in multiple stages.
The entire production process of these teas is full of interesting details (as well as myths), but this has already been well described by Konrad Pociask. Here, I would like to say a few words about roasting.
Roasting is an important stage in the production of rock teas, as it can enhance the flavor profile of the tea. In a recent study, published in the Journal of Food Composition and Analysis, researchers examined the compounds formed during the roasting process and their impact on tea flavor. Leaves from 20-year-old plants of three cultivars - Dahongpao, Shuixian, and Rougui - were compared in unroasted, lightly roasted (120 °C), medium roasted (130 °C), and heavily roasted (140 °C) versions, each roasted for 5 hours. It is worth noting that this was roasting with hot air to ensure maximum neutrality, although in actual production charcoal is used for roasting and the process is longer. Nevertheless, some findings of this study are interesting.
The Maillard reaction is a non-enzymatic browning reaction that occurs when amino acids and reducing sugars are heated together. The compounds formed in this process are often very diverse, responsible for, among other things, the aroma and flavor of bread, caramels, and fried meat. Tea leaves are rich in both sugars and amino acids, which is why the products of this reaction formed during roasting are potentially very important in shaping the aroma and flavor of rock teas.
Very often, compounds that give tea its flavor and aroma belong to esters and/or contain relatively high amounts of nitrogen. One such compound is indole, which is mostly formed during the stage of tossing withered leaves as a result of the activation of the beta subunit of tryptophan synthase (CsTSB2). The greatest number of aromatic compounds is formed during medium roasting; high temperatures promote the release of bound sugars, increasing the amount of Maillard reaction products.
One indicator of roasting can also be furfural, which is formed at each roasting level from simple sugars and theanine. Generally, theanine and polyphenols have a significant impact on the amount of aromas produced. Theanine is a substrate for pyrrole synthesis, and polyphenols, particularly EGCG and EGC, can undergo degradation to quinones, which catalyze two important reactions in the Maillard reaction - Strecker degradation and Amadori rearrangement. Based on the analysis of the formed compounds, it is possible to effectively distinguish tea from different cultivars. However, with heavy roasting, some already formed compounds undergo decomposition, more similar Maillard reaction products are created, and as a result, teas made from different cultivars lose their unique characteristics, forming a more uniform tea that is, however, flatter compared to less roasted versions.
The authors hope that the analysis of the concentrations of formed compounds may in the future be used to optimize rock tea roasting in a way that highlights the flavor qualities of the cultivar used.
