To start off, I've heard this expression used to delineate drinking fresh, green oolongs. It is logical to assume the 'original taste' of a tea plant would come through more clearly in a greener, and therefore less processed, tea. In contrast, there are more processed teas (i.e. darker, more oxidized, more rolled, more whithered etc) which I presume were originally so treated to preserve the tea for the long road between farm and market. These techniques were also used to coax out other textures or sensations that the plant is capable of producing. In this first interpretation of the term in question, the latter style of tea is presumably further from the original taste, because it has undergone more processing.
My argument against this interpretation is as follows: why are we not all drinking green tea, or white tea for that matter, or maybe puer, if minimal processing is the sole ingredient that original flavor is contingent upon. Or perhaps fresh tea leaves should be eaten straight off the bush?
I'm being a little cheeky about it, but my point is that I believe this first interpretation does not hold up under scrutiny. Tea is processed to bring out characteristics inherent in the leaf and make use of what the plant is able to offer us as drinkers. I think that in this sense, yuan wei has more to do with drinking tea that was processed with care, and crafted to align with the innate abilities of the plant itself. This is counter to relying on technique to force a tea into some preconceived or coveted taste. This kind of over-processing is apparent when one tastes a roasted oolong which is roasted beyond the capacity of the original material. When a tea tastes like only charcoal and no longer tastes like tea, then the roaster has overly relied on his/her ability to manipulate the flavor. This just ain't yuan wei.
In my humble opinion, an example of a well processed tea which achieve its yuan wei is a good Tie Guanyin. Good, traditional TGY is heavily oxidized, toilsomely rolled, and fired maybe four times over the course of a year. But this type of tea maintains its namesake which a light green TGY will not have. It tastes like iron! That's why it's called 'tie' 鐵- iron - guan yin, because it can give one an iron-like texture at the back of one's tongue. The peculiar sensation that you would get from sucking on a piece of metal. Although the cultivar is the same, this sensation is not available to the drinker when we drink TGY's less processed counterpart. It is innate in this cultivar of tea, but requires special coaxing on the part of the farmer to make it available to us drinkers.
So my conclusion after writing it out plainly in front of me is that 'he yuanwei' must originally have to do with the second interpretation. It may have been co-opted to sell green oolongs as the market has changed, which is fine. That's what tea does; it changes. But I feel good about my second meaning, which is to drink tea which has been treated with respect -- a respect, attentiveness and care for the plant as it is. That is what this phrase means to me.
NOAH
