Water for green tea, according to most accounts, should be around 80 °C to 85 °C (176 °F to 185 °F); the higher the quality of the leaves, the lower the temperature. Hotter water will burn green-tea leaves, producing a bitter taste. Preferably, the container in which the tea is steeped, the mug, or teapot should also be warmed beforehand so that the tea does not immediately cool down. Recently, green tea (as well as some black teas) have been shown to significantly increase interferon levels in tea consumers, which lends credence to the theory that some teas help boost the immune system.