Oolong. Wulong. Considered the most labor intensive tea to produce, oolong tea is arguably the most diverse tea category. A few terms which can dictate how oolong turns out are: fermentation or oxidation, roasting, man/machine ratio, cultivar, shape, and climate.
Climate. Tea farmers only have so much control over their crops, as is true with most agriculture. The variations from soil pH, altitude, rain, sun, and temperature will develop teas into something unique from season to season. There is no production line for growing tea. Plantations exist, but are still subject to climate variations. Climates vary all over the globe and can be factors in teas grown in India, Africa and Nepal, to name a few.
Shape: This refers to either pellet shaped or long and twisted physical form. I've read that the latter is the older and more basic form. However, the tightly-rolled pellet form tends to lock in aroma and preserve delicate leaf-bud systems (1 bud, two leaves on single stem).
Cultivar. I don't know much about this topic, however different cultivars express different characteristics. China and Taiwan produce some of the best oolongs in the world, and the variations of cultivar vary depending on geography. Some cultivars are natural, whereas others have been cross-bred for maximum production, or desirable flavor palettes.
Man/Machine. Men and Women have been tending the tea plant for many millenia. I'm uncertain as to how long, but they've been hard at work long before machines. Ultimately, there is no replacement for human hands and the energy and diligence they possess. Machine harvested tea plants can be outstanding. But in the larger picture, machine harvested oolong tends to be your mediocre tea, and 99.99% bagged tea. The true gems of oolong tend to be hand-harvested. Oolong can taste more consistent with machine harvesting, and that may be desirable for a marketed, mass-produced product. Conversely, hand-harvested teas have the ability to be handled more gingerly and more variably, thus giving each cup the possibility to be more expressive.
Roasting. As with any other plant, tea contains sugars, the end product of photosynthesis. Sugar can be transformed from it's natural crystalline state into more complex compounds. Culinary professionals have dubbed this "caramelizing", i.e. caramelized onions, creme brulee, caramel. When tea is roasted, it is essentially caramelizing the sugars within the leaves. Roasting can play big role in the end product depending on roasting parameters, which include: length of time, repetition, and source of heat. The longer the tea is roasted, the more caramelizing that occurs. Lightly roasted teas will only have hints of "toasty" character, whereas heavily roasted teas will taste very "toasty", and usually appear a darker hue. Tea can be re-roasted, which typically takes place on an annual basis if at all. The source of heat can be charcoal, wood embers, an oven, or even tea stuffed inside of bamboo which is roasted whole.
Fermentation. Also known as oxidation. The first thing I think about is a browning apple. core... Fermentation may be considered the largest factor of how the end product will turn out. Oolong resides between green tea and black tea (red tea [China]). As such, oolong can be a pale yellow or a reddish orange color when brewed. The amount, or percentage of fermentation, creates a vastly different flavor. Basically, when the tea is plucked from the plants, they will naturally start to decay. Enzymes, or cellular catalysts, start to break down cell contents. This is accelerated by bruising the tea leaves after they have dried out a bit in the sun. Once the leaves are bruised, fermentation can be halted immediately or last for about 48 hours. Halting takes place by the application of heat, either by ovens or woks, but is almost always a flash application (like pasteurization, but with different objective). The objective is to denature, or destroy active enzyme activity which will keep the tea from fermenting, or oxidizing further. The term oxidizing refers to the idea that oxygen is needed to facilitate fermentation, also know as an aerobic reaction (requiring oxygen). Some oolongs exist which are anaerobically produced (oxygen-deficient environment), such as GABA oolong which is fermented in a n environment. Enough said.
With all the variables combined, there is an indefinite combination of possibilities. For this reason, many teas are produced under a recipe. This is done so people can enjoy Tie Guan Yin, WuYi Rock Oolong, Dong Ding, Big Red Robe, year after year with only minor variations in quality and taste.
Now that Oolong has been revealed from the plant to the end product, the final excursion lies in brewing techniques. To be continued...