Preparation is really really simple. Place tea leaves in the teapot, and put enough ice-cubes on the leaves to make the teapot full. And, just wait until ice-cubes thaw. You can leave it either in the room or the fridge. I sometime leave it in the refrigerator overnight. Next morning, ice-cubed tea with a lot of Umami is ready.
As you may know Umami is extracted with lower temperature water, while pleasant bitterness comes out by higher temperature water. So, using ice-cubes helps extract full of Umami. For this method, tea containing Umami such as high-quality Sencha and Gyokuro are recommendable.
In addition, caffeine goes down to about one third. Also, I enjoy “Mizu-dashi” method, which is the tea using water.
Check my old post.http://japaneseteastory.blogspot.jp/2011/05/iced-japanese-tea.html