Caffeine content varies by beverage type and preparation Tea varieties. Black, green, and white teas are prepared from leaves of the same plant, Tea preparation. The preparation method greatly impacts the caffeine content of tea. Coffee varieties. An average 8-ounce (237-ml) cup of coffee Caffeine Content of Selected Foods, Drinks, and Drugs. 1. Serving sizes are based on commonly eaten portions, pharmaceutical instructions, or the amount of the leading-selling container size. Source: Center for Science in the Public Interest..