Green and oolong teas, along with white and black teas, all originate from the tea tree, or Camellia sinensis. The tree is an evergreen that grows in tropical and some subtropical regions, including parts of India, China and Sri Lanka. It can reach a height of 50 feet, but is pruned to become a spreading shrub with easily harvested leaves. What makes a tea "oolong" or "green" depends on how the leaves are processed, and not on the species of plant the tea is derived from.
Manufacture of Green Tea
Green and white teas are the "youngest" of the tea types. White tea is made with young leaves and even buds, and green tea is gleaned from somewhat older and larger leaves. In some cases, harvesters allow green tea leaves to shrivel slightly before processing them, according to the Linus Pauling Institute. The leaves are then fired or steamed to stop the process known as oxidation.
Manufacture of Oolong Tea
Harvesters lightly roll or break oolong tea leaves after gathering them, a process known as bruising the tea leaves. They also leave them to age longer than green tea leaves. Like green tea, oolong tea is eventually steamed or fired. The production of oolong tea lies somewhere between the immediate and gentle processing of green and white teas and the complete bruising and oxidization of black teas.
Caffeine Content
Green and oolong teas are similar in their caffeine content, which is between 9 and 50 mg per 8-oz. cup. Both teas have less caffeine than most black teas, which are still lower in caffeine than coffee. On average, tea contains about half as much caffeine as coffee.
Medicinal Properties
Green and oolong teas are rich in different kinds of flavanols, natural compounds found in plant foods that contribute to good health. Green teas are highest in catechins, while oolong tea is the richer source of theaflavins and thearubigins, although it falls short of black tea. In general, tea is considered to be of "modest" protection against conditions such as heart disease or stroke, according to the University of Oregon. Promising studies have been done on the relationship between specific types of tea components and specific cancers, as well as on conditions like osteoporosis. Both green and oolong tea were linked to higher bone density in one study, the university notes.
Dental Health
Both green and oolong teas contribute toward the recommended amount of daily fluoride to prevent cavities, notes the Linus Pauling Institute. Recommendations vary between 1 and 4 mg of fluoride, depending on age and gender. One liter, or four cups, of green tea a day yields between 1.2 and 1.7 mg of fluoride, while the same amount of oolong delivers between 0.6 and 1.0 mg of fluoride.
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