By definition, a green tea is a type of tea that has not undergone the withering and oxidation process of oolong or black tea. There are many diverse varieties of green tea. They differ in the growing conditions and methods as well as the plant variety (cultivars) and production method used. Once the tea is harvested it is shaped and fired which stops the oxidation process. In China, the teas are usually pan-fried or roasted, whereas in Japan they are usually steamed. Each method yields a completely different flavor profile, ranging from sweet, creamy and grassy to toasty and nutty. Generally, green tea is more sensitive to time and temperature in brewing. Tea that is steeped too hot or too long will release excessive amounts of tannins leading to a bitter and astringent brew.