The traditional method of making tea in Britain has always been to let the tea brew for at least five minutes. A recent study has now found that tea which is brewed for longer has higher concentrations of flavonoids and shows more antioxidant activity than tea that is only briefly brewed. Scottish researchers brewed three grams (equivalent to one UK tea bag) of each of six different brands of tea in 300 ml of freshly boiled water. The tea was infused for three, five, seven and ten minutes. The flavonoid content and antioxidant capacity of the resulting liquid was then measured. Both were found to increase with infusion time, with a plateau after seven minutes. The seven-minute infusion had 60% more flavonoids than the tea that had been infused for three minutes. The measured increase in antioxidant activity correlated with the flavonoid content and was not affected by the addition of milk. The different brands of tea were equivalent.

A second part of the study examined the physiological effect of drinking tea. Nine healthy male volunteers were randomly assigned to three groups and consumed three different beverages (black tea, black tea with semi-skimmed milk, or water with semi-skimmed milk), on three different occasions, one week apart. Consumption of black tea (400mL - equivalent to two cups) was associated with significant increases in plasma antioxidant capacity (10%) and the level of flavonoids in the volunteers' blood rose by up to 45%. The findings were unchanged by the addition of milk.

Effects of infusion time and addition of milk on content and absorption of polyphenols from black tea. J Agric Food Chem. 2007 Jun 13;55(12):4889-94.