Of all the commercial sources of caffeine, guarana paste has the highest concentration of the pure compound, about 4%. Guarana paste is made from the seed of the Paullinia tree, found primarily in Brazil. More common sources of caffeine contain lower concentrations of the compound: 1.1-2.2% in coffee beans; 3.5% in tea leaves; and 1.5% in kola nuts. Other less common sources of caffeine include maté leaves, obtained from the Ilex plant (less than 0.7% caffeine), and yoco bark, obtained from the Paullinia yoco tree (2.7% caffeine).
Because of the way in which these foods are prepared, the above data do not give an accurate picture of the amount of caffeine that people consume. The average cup coffee, for example, contains approximately 100-150 mg of caffeine; the average cup of tea, 50 mg of caffeine; and the average cup of cocoa, about 5 mg of caffeine. Cola drinks tend to contain 35-55 mg of caffeine, and the average chocolate bar contains about 20 mg of the compound. In 1997, more products were introduced that contained caffeine including bottled water and chewing gum.