Browsing Google Books I found a very interesting quote from the 1846 book The Chinese, by Sir John Francis Davis:
Young Hyson, until it was spoiled by the large demand of the Americans, was a genuine delicate young leaf, called in the original language Yu-tsien, “before the rains,” because gathered in the early spring. As it could not be fairly produced in any large quantities, the call for it on the part of the Americans was answered by cutting up and sifting other green tea through sieves of a certain size; and, as the Company’s inspectors detected the imposture, it formed no portion of their London importations.
I had always assumed by what is currently passed off as “Young Hyson” that my tea-drinking ancestors simply had terrible taste. 🙂 I suppose the next question would be, what kind of Yu Qian (雨前) tea did they dump in Boston Harbor during the Boston Tea Party? 🙂