Today, inspired by a discussion in the TeaDay topic, I made some green tea with peppermint and cardamom. Among other things, I clearly screwed up the balance between the mint, green tea, and cardamom--too much peppermint--and it ended up just tasting of peppermint.
I noticed a certain off-flavor fairly after the tea had sat for 15 or 20 minutes, which is sooner than a medium quality green tea like I used normally changes flavor. It might have been some astringency from the green tea, but I used a quite low steeping temperature that should have prevented that.
So it brought up a question that maybe someone here can answer: does peppermint tea--infused from real peppermint leaf--lose flavor faster after steeping than most other herbs?