Huigan: the sweetness that returns
Huigan (回甘) is Chinese for returning sweetness: a sweet, cooling feeling that rises at the back of the throat a little after you swallow a good tea, often after a moment of bitterness.
What huigan feels like
Huigan does not arrive with the sip. The tea may first taste bitter or astringent; then, ten or twenty seconds after swallowing, a sweetness appears at the back of the mouth and throat, sometimes with a cool, lingering feeling and more saliva. Tea drinkers in China treat it as one of the clearest signs of a good leaf, and it is most associated with raw pu-erh and some oolongs.
Where it comes from
Huigan is not sugar in the tea. It is the way your mouth responds once bitter and astringent compounds, such as polyphenols, have passed: the contrast makes sweetness more noticeable, and saliva returns. Well-grown leaf, often from older trees, tends to show it more clearly, while poor or over-steeped tea leaves only bitterness behind.
How to notice it
Brew a raw pu-erh stronger than is comfortable, for example thirty seconds at 95°C in a small gongfu vessel. Drink the cup, put it down, and do not drink or eat anything else. Breathe through your nose and count slowly to twenty. If the bitterness turns into a sweetness at the back of your throat, that is huigan.
Huigan in Box I
The last session of Box I is built around this moment. Session seven brews the Sheng Puer gongfu style, strong on purpose, and asks you to wait. The bitterness you met in session four comes back as sweetness.