Why does black tea contain more caffeine than green tea?

black tea uses older tea leaves and green tea uses younger leaves where the caffeine has lower concentrations And you should also know that tea leaves are not roasted like coffee beans. The coffee bean is black because it has been roasted, but black tea leaves are black because they have been allowed to ferment over time and then they are dried and shredded. The leaves turn black during the fermentation, much like how olives turn black when they are fermented. It you tried to roast a leaf, you would either set it on fire or get something nasty like toasted tobacco leaves