Bitterness is one of the natural characteristics of green tea, particularly fine Japanese teas. It is directly related to the levels of caffeine and catechins found in the leaves. Bitter flavors are actually highly prized amongst Japanese tea experts. Some varieties of green tea are less bitter than others, which can be seen in the flavor chart for each tea. For example, shiraore is low in caffeine compared to other green teas, and is therefore less bitter. Excessive bitterness in tea can also result from either brewing your tea for too long, or brewing the tea with water that is too hot. While it can be tempting to brew the tea as long and hot as you can to extract as much as possible from the leaves, this can result in something that is undrinkable. For the best results, carefully follow the instructions on the back label of your tea. If it is still too bitter for your taste, feel free to try a lower water temperature or shorter brewing time.