One thing I haven't seen addressed: with black tea I use one steeping,
or occasionally two. With green tea I use up to seven steepings. I
think what I do may be typical of a lot of others' practice. If so,
it would seem to be that even if black and green tea start out as
essentially the same in caffeine, the later steepings of green tea
would have less. Toci

Which is of course why you must increase the steep time, each time. I
always thought I lost almost all the caffeine in the first steep. But now,
if those studies are right, it seems that you can get fairly consistent
caffeine on subsequent steepings by increasing the time a minute or so each
time.