Green tea requires special attention to water temperature because its structure is more delicate than that of other teas. Because it is not oxidized, it retains a high concentration of heat-sensitive plant compounds.
Using boiling water tends to extract certain elements too quickly, particularly those responsible for bitterness and astringency. The result is often unbalanced: a harsher initial taste that can mask the tea's more delicate aromas, such as its vegetal, iodine, or umami notes.
Lowering the temperature allows for a more gradual and precise extraction. The tea then expresses itself with greater sweetness and complexity, without being dominated by bitterness.
However, there are some interesting exceptions. For teas like genmaicha or hojicha, where roasted notes and a rich aroma are desired, hotter water is perfectly suitable. The heat allows the aromas to be released quickly and to rise more intensely to the nose. In this case, there's no need to extend the brewing time: a short infusion is sufficient to obtain a balanced result, both fragrant and pleasant on the palate.
Each green tea has its ideal temperature, but generally speaking, avoiding boiling water is a simple way to respect the delicacy of the leaves and reveal their true character.