Harold McGee, sur Curious Cook, explique pourquoi l'eau doit être servie bouillante sur du thé noir, mais seulement à 65° sur du thé vert :

In the course of their analysis, the chemists also discovered a new reason for the traditional practice of brewing black tea in a preheated teaot with water just off the boil. High-temperature brewing does the best job of extracting aroma compounds from the tea leaves, but it also generates even larger quantities of certain aromatics than were in the leaves to begin with! It may do so by breaking off small, aromatic portions from much larger molecules. By contrast, we brew green teas in water far below the boil (around 150 degrees F, 65 degrees C) to preserve their more delicate, simple aroma and color.