The effect of processing parameters, namely extraction time, carbon dioxide flow rate, temperature, pressure and particle size were investigated and conditions giving higher caffeine yield were recorded. Firstly, in order to determine the effects of total CO2 and extraction time on the yield, extraction experiments were carried out for extraction time varying between 1 and 10h. Other parameters such as extraction temperature of 55◦C, carbon dioxide flow temperature giving the maximum caffeine extraction at these conditions was found by changing the temperature between 55 and 75◦C. Fig. 4 shows the effect of extraction temperature on the caffeine yield. The caffeine yield increased with increasing temperature up to 60◦C and then decreased for further increase in extraction temperature. The increase of temperature up to 60◦C
waseffectivetodissolvecaffeinemoleculesandtoincreasecaffeine yield. It is thought that the decrease in the yield at higher temperatures arises from the drying of tea stalks and the lowering of thedensity of CO2as we go from 60 to 75◦C.