All tea that originates from the tea plant (camellia sinensis) contains a type of metabolite known as a flavonoid. This is frequently cited as having potent health benefits. Green, black and oolong tea contain a similar amount of flavonoids, although the oxidization or fermentation process, that effectively changes green tea into black tea, can alter the state of these flavonoids. These complex metabolites are known as theaflavins and thearubigins and are less potent than their simple cousins. This means that black tea is less potent and hence less popular for those seeking health benefits.
Whilst green tea seems the most sensible health option the total lack of fermentation makes it harder on the stomach.
For this reason the Taiwanese have created a range of fermentation for there tea, giving them the best of both worlds with there Oolong Tea.
Oolong tea covers a wide range of taste, from very light to nearly coffee strength true to a chocolate flavour which is a rare combination and contains an abundance of simple flavonoids.