What is the fine-grained topic of the following text: So infusing green tealeaves with cold water brings out their innate sweetness, enhanced even further when you pile your glass or ceramic kyusu (the traditional small Japanese teapot, made of earthenware, stoneware or porcelain) with ice on top of the tea leaves. Only return the topic.
Infusing green tea leaves with cold water in a Kyusu teapot