Saying that "tea temperatures are supposed to be x" is like saying that "food should be cooked at x". But regardless, if you go to a good tea shop you are likely to have a pot of freshly boiled water placed in front of you, which some folks in this thread consider an unnacceptable hazard worthy of a lawsuit.
Technically, it depends entirely on the tea. Black teas are universally recognized to require the highest steeping temperatures, to the point that high-altitude brewing is a problem because the boiling point of water is too low. Sweet, amino-heavy teas like a good gyokuro are definitely better done at lower temperatures. But most green teas are quite forgiving, and are commonly brewed at near boiling temperatures. Freshly boiled hot water is also often necessary for herbals, especially short-steeping acidic herbals like hibiscus.
And none of this has anything to do with catechins, which are not significantly more stable at 170 deg F than they are at 200. Theaflavins on the other hand are quite unstable, but they start degrading at temperatures lower than any accepted steeping temperatures, so losing them is unavoidable.
> In essence, the researchers found that in solution, both green tea catechins and black tea theaflavins are unstable and have a tendency for rapid degradation, especially at high temperature or basic pH.
> The thermal stability of catechins is better than that of theaflavins. For example, after a 3 hour open-air storage in a water solution, the amount of catechins and theaflavins was not found to have decreased at 24 °C, whereas catechins had a 25% reduction at 70 °C and a 29% decrease at 100 °C; theaflavins on the other hand had a 56% decrease at 70 °C and amounts were undetectable at 100 °C after 3 hours. The discrepancy in the aqueous stabilities of catechins and theaflavins can be postulated to be due to the large difference in chemical reactivity between the two groups of compounds: relative inertness and less steric hindrance of catechins vs. higher reactivity, especially anti-oxidant activity because of the ring-fusing, increased number of hydroxyl groups and steric hindrance surrounding the benzotropolone core.
Technically, it depends entirely on the tea. Black teas are universally recognized to require the highest steeping temperatures, to the point that high-altitude brewing is a problem because the boiling point of water is too low. Sweet, amino-heavy teas like a good gyokuro are definitely better done at lower temperatures. But most green teas are quite forgiving, and are commonly brewed at near boiling temperatures. Freshly boiled hot water is also often necessary for herbals, especially short-steeping acidic herbals like hibiscus.
And none of this has anything to do with catechins, which are not significantly more stable at 170 deg F than they are at 200. Theaflavins on the other hand are quite unstable, but they start degrading at temperatures lower than any accepted steeping temperatures, so losing them is unavoidable.
From https://pubs.rsc.org/en/content/articlehtml/2013/fo/c2fo3009...:
> In essence, the researchers found that in solution, both green tea catechins and black tea theaflavins are unstable and have a tendency for rapid degradation, especially at high temperature or basic pH.
> The thermal stability of catechins is better than that of theaflavins. For example, after a 3 hour open-air storage in a water solution, the amount of catechins and theaflavins was not found to have decreased at 24 °C, whereas catechins had a 25% reduction at 70 °C and a 29% decrease at 100 °C; theaflavins on the other hand had a 56% decrease at 70 °C and amounts were undetectable at 100 °C after 3 hours. The discrepancy in the aqueous stabilities of catechins and theaflavins can be postulated to be due to the large difference in chemical reactivity between the two groups of compounds: relative inertness and less steric hindrance of catechins vs. higher reactivity, especially anti-oxidant activity because of the ring-fusing, increased number of hydroxyl groups and steric hindrance surrounding the benzotropolone core.