Brewing
Generally, 2.25 grams of tea per 180 ml of water, or about a teaspoon of black tea per 6 oz. cup, should be used. Unlike green teas, which turn bitter when brewed at higher temperatures, black tea should be steeped in freshly boiled water. The more delicate black teas, such as Darjeeling, should be steeped for 3 to 4 minutes. The same holds for broken leaf teas, which have more surface area and need less brewing time than whole leaves. Whole leaf black teas, and black teas that will be served with milk or lemon, should be steeped 4 to 5 minutes. Longer steeping times make the tea bitter (at this point, in the UK it is referred to as being "stewed"). When the tea has brewed long enough to suit the tastes of the drinker, it should be strained while serving.
The ISO Standard 3103 defines how to brew tea for tasting.
Read more about this topic: Black Tea