What you want to ask is why osmanthus oolong is red after cooking. The reason is mainly related to the oxidation reaction of tea. Oolong tea is a semi-fermented tea, which has been treated by shaking, deactivating enzymes, rolling, fermenting and baking. In this process, the enzymes of tea come into contact with oxygen in the air, which triggers the oxidation reaction of tea. Osmanthus fragrans, as one of the components of oolong tea, will release a rich fragrance of Osmanthus fragrans when cooking tea and react with the chemical components of tea. Osmanthus fragrans contains a lot of anthocyanins, which interact with tea polyphenols and other components in tea to produce new compounds, making tea soup appear red.