I first learned tea in Taiwan, from one of the chief proponents of the smelling cup (along with tasting cup) for drinking Pu-Erh tea. The tea tasting cup set was developed for drinking High Mountain Oolong tea primarily. It was a way of booth aerating the tea, cooling it slightly for drinking and providing a narrow point of focus for evaluating tea fragrance and such.
Among professionals, it is believed that we should be able to identify the tea mountain simply by smelling the tea. Some more practiced tea buyers will be able to identify individual farms or even specific roasters based on the simple waves of the beaker in front of their nose. This may not account for what is known as great skill (Kung fu) in tea culture, but it is a good start.
In keeping with the views of my teacher, Pu-Erh, and especially aged Pu-Erh tea, is extremely fragrant. We must concentrate and in a sense slow down in order to be able to perceive the intricacies of their aroma. The ability to perceive these micro details in turn set up a certain architecture in the mind, which then allows us to evaluate the origin, quality, age, and purity of a tea without any additional information being provided.
The secret — I find — in being able to fully perceive the quality of a tea through scent, is to take enough time with smelling. Different teas reveal themselves at different temperatures and so we catch the rhythm of the aroma at different points. The moment of recognition often happens slightly after the point where most people give up or switch to sipping. It is, all the same, one of the surest ways of tuning the mind into the vibration of a given tea — the Cha Yun (茶韻).
If you don’t have smelling cups or prefer one of the tea styles which spurns them, then the lid of the gai wan, the empty tea pitcher or the tea pot itself will provide a clear read of the tea. Exploring this technique will greatly expand (more than double) our ability to know a given tea. The degree to which we expand our subtle awareness in the tea brewing process, the finer and more nuanced our tea will be.