So i've ordered 2 different brands of gynostemma (or jiaogulan in chinese) and they each taste very differently. The first one I've ordered tastes extremely bitter, the second one I've ordered tastes light and sweet, even though I can detect somewhat of a similar bitter after taste.  According to the boxes they are both 100% gynostemma leaf, and the tea bags appear to be exactly the same in size. Why does one taste very bitter why the other one doesn't? Is it possible the leaves from the first box were older when i ordered them? 
"However, it is known that the chemical constituents of GP planted in diﬀerent areas are very diﬀerent in composition.17,18 Furthermore, there are two taste variants, sweet and bitter, for GP herbs, which have diﬀerent clinical application in folk medicine in China.18-21" Chemical Differentiation of Two Taste Variants of Gynostemma pentaphyllum by Using UPLC–Q-TOF-MS and HPLC–ELSD Jing-Guang Lu†‡, Lin Zhu‡, Kate Y. W. Lo‡, Alexander K. M. Leung‡, Alan H. M. Ho‡, Hong-Yang Zhang§, Zhong-Zhen Zhao‡, David W. F. Fong‡, and Zhi-Hong Jiang*†‡ J. Agric. Food Chem. 2013, 61, 1, 90–97 https://pubs.acs.org/doi/full/10.1021/jf304154d 