It seems every time I make a cup of green tea, if I don't finish it while it's still considerably hot, it starts to get really sour and tastes awful.
Why is this and how can I prevent this? What am I doing wrong?
The most likely culprits are:
Here is an excellent resource for getting these factors right:
Green tea does not require much time. Too long a steeping time will result in more bitterness and a less balanced flavor. We recommend experimenting with a range of 1 - 3 minutes. Japanese green teas generally taste best at 1 - 2 minutes while Chinese green teas seem to prefer 2 - 3 minutes (the smaller leaves of Japanese teas will extract faster than the generally larger leaves of Chinese teas). Steeping time should be balanced with water temperature: the lower the temperature, the longer the tea can be steeped.
As a general guideline, green teas taste best when brewed at temperatures between 140°F - 185°F (60°C-85°C). The grade of the tea and the time of its harvest will also influence the appropriate steeping temperature. Green teas picked earlier in the spring will benefit from lower temperature brewing due to their overall higher levels of amino acids.
The most accurate way is to use a thermometer to measure the temperature of the water in the kettle. One approach is to heat the water in your kettle to the desired temperature and then pour it into your teapot. Another approach is to heat the water to boiling and then let it cool down a bit before pouring into your teapot.
Read the whole thing for further background.
The tea will have brewed to long. If you remove the leaves when the tea is just brewed correctly, or use a tea pot and pour the tea once brewed this won't happen.
A Chinese friend of mine says that you need to rinse green tea leaves with boiled water before steeping.
In my personal tea drinking experience, If the green tea tastes sour, it always caused by dirt or storage. For clean green tea often tastes a little bitter and smells fragrant at first, then tastes a little sweet.
the bad quality tea would cause this, i have drank tea over 7 years, i did not have this problem, even i put ice block into my green tea, it taste bettern then.
You can read more about how to brew green tea here.