The chemistry of tea is complex KS5 stuff. Investigate Manganese content by an oxidation to purple Manganate VII and a colorimeter, or else extract the caffeine; maybe detect the tannins or try enzymes on the polyphenols. For younger KS2-3 pupils why not use the "cuppa" as a real context for those cooling curves, or link to the insulating nature of the cup with metal,enamel, china and polystyrene mugs. Likewise, at KS3, try basic solubility or rate investigations with sugar powderlumpsquantities) and tea (hotcold). Finally, try to see how milk affects the taste, are you a pre or post-lactarian? Set up a simple taste panel: two with milk in the cup before the tea, one with milk added after. Can anyone spot the odd one out and understand why?