The optimal Xp/Xo ratio represents a Xk (amount of caffeine inside cell walls) around 4 times higher than Xp (readily accessible caffeine), denoting that caffeine is strongly bond in the vegetal matrix. Furthermore, this is in accordance with the fact that a very short constant extraction rate period was observed in the extraction curves (tCER values were 0.96, 0.16 and 0.30 min, respectively, for EA, EL and ETOH) and thus, mass transport within the solid phase dominated extraction rate almost from the beginning of the process. In this respect, the solubility value (Y*) calculated as the slope of a theoretical linear behavior up to 14 min of extraction should be considered as an estimated value.