Kinetics and equilibria of tea infusion, Part 15. Transport of caffeine across a teabag membrane in a modified rotating diffusion cell

The rates of transfer of aqueous caffeine through a membrane of teabag paper were measured by means of a modified rotating diffusion cell. The reciprocals of the transfer rates were found to be directly proportional to the inverse square root of the rotation speed. These results are consistent with the rate-controlling step being diffusion of caffeine through the Nernst diffusion layers on each side of the membrane. At both 25 and 80°C the resistance to transfer through the teabag membrane itself was negligible, showing that the material was well suited to the brewing of tea, coffee or other food materials.