Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants, as well as enhancing the reward memory of pollinators.
Coffee naturally contains caffeine, and the process of brewing coffee extracts caffeine in the beverage. Coffea Arabica contains 1.5% caffeine on average, compared to Coffea Canephora, (Robusta), which contains about 2.7% caffeine.
The coffee brewing method is also important for extracting the caffeine. The amount of caffeine extracted will also vary depending on brewing temperature, grind size and brewing time. All these parameters are well known constants, and are different for the various brewing methods.