I found you folks by searching for a name to put on the green tea I had a sip of (and then threw out the rest of my cup of) that had a very strong seaweed flavor to me. I want to know what to avoid -- I've run in to that flavor in green tea a few times, and don't like it at all. It's not what I expect from any tea, or what I'm looking for when I get a green tea. So is that flavor a sign of old tea, or something else? And I see now I'll have to read up on your teas.
This is what I wrote in response.
Thanks for your question.
First, I have to say that I've never had a green tea that tasted like seaweed, so I can only speculate as to where that taste would come from.
Our green tea has a grassy or "earthy" flavor. This is a sign not only of quality tea plants, but also of a tea that was processed right after harvest and so underwent minimal oxidation and fermentation. These break down the catechins and other polyphenols that occur naturally in tea leaves.
In other words, a grassy taste means that the tea has plenty of good stuff in it.
I have found, on the other hand, that some green teas don't have that grassy flavor, possibly because they've undergone some oxidation or fermentation due to some aspect of how the tea is processed after harvest. (But they still don't taste like seaweed to me.) For instance, I've had a green tea whose leaves were green but which produced a brown infusion that tasted nothing like green tea to me.
Most of the green teas I've had that I would call just plain lousy (but, even then, not "seaweedy") are mass-marketed bagged teas. In that case, the causes are (1) the low-quality tea (know in the business as "dust") that's in the bag and (2) how long the tea's been sitting in a warehouse or who-knows-where.
If you remember the brand of tea you had, please let me know, and I'll try to do some research. Maybe I've been fortunate to have never run across such a tea, or maybe it's something I've grown accustomed to and don't even notice anymore. That's why I was so surprised, in reading that article, to hear green tea in general described as tasting like seaweed.