Simple question really - why is it I can reuse green tea leaves 2-3 times with minor degradation in the quality of tea, but I can't do the same thing with black tea?
Is it because the black tea has oxidized?
I've noticed that you can also reuse Chinese red tea leaves as well (fermented green tea) without a problem.
I've never had an issue reusing anything that's real tea (black, oolong, green). Perhaps there is another factor here? If you're black tea is coming out of a tea bag, or a lower "grade" then the green tea leaves you're using that might be a reason that it isn't coming out desirably.
Generally speaking it's an issue of grade rather than the type of tea. The finer the tea, the more likely you are to extract everything in the first run. Take apart a cheap tea bag, and you'll notice that the leaves are powder or almost powder. A full leaf (you can buy any black tea from a reputable shop in a higher grade) will extract more slowly and give you a better flavour and probably yield to better second or third runs.
My grandmother always drank black tea from store-brand or Lipton tea bags, and she always reused them and didn't say anything about the taste.
My current favorite black tea is pu-erh tea from Prince of Peace brand tea bags. I use two tea bags in an extra large tea mug, steep exactly 3 minutes, and use the tea bags three times. I tried using four or more times but sometimes cup #4 is a bit weaker. I honestly don't see much difference between batches.
I have read that the caffeine content goes down in the cups after the first. In fact, in the book "Lose weight with green tea" by Patricia Rouner, it is suggested that steeping a fresh tea bag in hot water for about 50 seconds, then discarding the water removes most caffeine but keeps most of the antioxidants so you can decaf your own tea at home.
I store my used tea bags on a plastic soap dish that has a grid to help the soap dry. This lets the tea bag dry out some between uses.
I might add, however, that if you are drinking tea for the medicinal benefits, you might try using fresh tea bags each time to ensure the maximum antioxidants, and see if that helps your health problem more than drinking tea from reused tea bags.
Long steeping makes for bitter tea. I suspect that you will find that the second batch of tea either has no flavour, or is more bitter.
Note that tea making is very depending not only on steeping time, but on temperature. There is good reason to pre-heat china teapots before making the tea -- especially if you live in a country like England where room temperatures in winter are measured in the 50's (F).
