https://www.valleybrooktea.com/post/why ... taste-sourIf leaves are under-fermented, the final product would taste very “green” and grassy. If leaves are over-fermented, it’s very likely that the final tea soup tastes sour.
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Drying requires heat, and heat needs to be created. If the heating up process takes too long, it’s possible that tea leaves get fermented again and develop the sour taste.
Therefore, in Tongmu tea-making, a unique step called “Red Pan” is used to prevent leaves from over-fermentation. “Red Pan”, or 过红锅 (pronunciation: Guò Hóng Guō, meaning: passing the red pot), uses heat to kill off enzyme activity to stop leaves from fermenting. (Yes, it’s very similar to “kill-green/杀青” in green tea and oolong tea.)
On the other hand, the sunny dry hong from yunnan is expected to have sour notes that go away and transform with some age, as described colorfully here
viewtopic.php?p=41179#p41179I'm asking because when I was at our Fengqing tea farmer years ago and he was making his Yesheng Hong ( wild black ) , the fresh tea leaves were in big plastic crate covered by thick , but breathable , canvas. When he opened it , the disgusting sour ( almost like somebody had puked ) odor came out. ( the similar notes of sourness you can experience in fresh made Shai Hong - sun dried blacks , as they are not high heat processed after so these notes are imprinted in taste , yet they will diminish by some time and turn to sweet jam like taste )
And it seems that the sour sunny dry may be more suitable for aging than those that get the high temperature treatment, which adds some choco notes, as hinted by this post:
https://www.pageoftea.com/smart-tea-drinkerSome of them have applied final high temp. roasting for short time , called “ti xiang” or “gao xiang” , that makes cocoa – chocolate hint in flavor spec. of the tea. There is also “shai hong” ( Sun dried ) processing of black tea, which is different from the previous two and it’s suitable for further ageing for certain time.
What are your thoughts on the sour notes in black tea?
Personally, I don't mind them as long as they are well balanced, and are more fruity than straight up sour.