A question on Steepster that I think it's worth sharing here

I just saw the following question on Steepster's discussion board. I shared my anwser to the question and I think it's worth while to share it here on the blog too.

From Steepster:

 

" Sakura said about 11 hours ago

Is this normal - long jing?

I recently purchased a long jing tea and I noticed that if I leave the cup overnight with tea in it, there’s an oily film that forms on top?
I was just wondering if this was normal?
I stumbled upon this:
http://worldoftea.org/bp-tea-or-why-is-there-an-oil-slick-in-my-tea/
but I’m still a bit unsure. I guess it’s from the oils they use when they pan fire the tea though. "

Link to Steepster: http://steepster.com/discuss/1977-is-this-normal-long-jing

And my answer:

This is normal if you see the oily film appear overnight. It is not normal if you see any oily stuff floating on your tea you just steeped/brewed.

The oily substance on your overnighted tea is oxidized tannin compound. Tea naturally contains tannin. It is what gives tea its astringency taste. Tannin from tea is perfectly safe to consume. But when tea sits for a period of time (sometimes as little as an hour), the tannin in the tea liquor reacts with oxygen from the air to form the oily stuff you see. These oxidized tannin compound is bad for you. They interrupt with nutrient absorption and irritates your stomach.

This is a perfect example of why we gongfucha drinkers always advocate other tea drinkers to enjoy their tea while it’s still hot. Some people drink tea for its health benefits. Some drink tea for pleasure. But nobody wants the tea they drink to cause harm to their health. Right?

For the same reason mentioned above, I also recommend AGAINST keeping steeped tealeaves overnight to be steeped again the next day . It’s bad for you. Gongfucha drinkers don’t let their tealeaves cool too much inbetween steeps, and we usually don’t re-steep wet tealeaves that’s already cold. These are all traditions taught to us from our elders. In the past tea wasn’t analyzed with science like we do now so the elders couldn’t tell us why. They just learn from experience and drilled these traditions into our head. Now with modern science we know these thousand-year-old wisdoms are no joke.

By the way, Iced tea should be cooled quickly in sealed container to minimize oxidation of the tea liquor. And for those who drinks bottled tea……umm……you figure.

Now, if your see oily substance floating on hot tea that’s just steeped, that could be anything. What Worldoftea.org says on their website about tea oil used in pan firing is true. But the amount of oil used is very very little, so little that if you were to wipe the pan with a paper towel after the oil is applied you would not see a trace of oil on the paper towel. I have never seen oil floating on any just-steeped pan-fired tea, or any tea before. Safe to drink or not aside, it is not normal.

We always recommend rinsing your tea before you actually steep it, no matter what type of tea and how good/fresh/expensive it is. Even with tealeaves from our well-known partner tea farm that were picked and processed in our presence so we know they are clean and high quality, we still rinse them. It’s another gongfucha tradition. (Maybe i’ll write a blog post to explain this when I have time).