Despite what many erroneously believe, green teas do not necessarily have less, or more, caffeine than black teas. Some will argue that green tea has 1/3 the caffeine of black tea while oolongs are slightly more caffeine-rich with 2/3 the caffeine of black tea, but this is simply not true. Caffeine content is not related to level of fermentation; instead, it is more closely aligned to the type of leaf used.
The bud and first leaf of the tea plant contain the highest concentration of caffeine, between 4 and 5% of the total dry weight, and the second leaf contains about 3% of the total dry weight. Thus, the desired "two leaves and a bud" plucking contains caffeine that is approximately 4% of the dry weight. When these teas are infused for 5 minutes, 40-50 milligrams of caffeine dissolve into the water.
The specific variety of tea bush that is used also plays a major role in the amount of caffeine in tea. Green teas are generally produced from Camellia sinensis sinensis shrubs (China variety), and these leaves have a tendency to be slightly smaller than those produced from the Camellia sinensis assamica shrubs (Assam variety) -- used primarily for black teas. These China varietal teas may have a slightly lower caffeine content.
Per weight, coffee beans have less caffeine than tea leaves, but more coffee grounds are used to brew one cup of coffee. Thus, while tea has more caffeine by weight, it has less caffeine than coffee when infused. When compared with a cup of tea, a cup of coffee can have two to four times as much caffeine.
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