Cookie, another OZ friend asked me the exact question
I've never thought about it until now. Hahaha.
Info on wiki: Grass jelly is made by boiling the aged and slightly oxidized stalks and leaves of Mesona chinensis (member of the mint family) with potassium carbonate for several hours with a little starch and then cooling the liquid to a jelly-like consistency.This jelly can be cut into cubes or other forms, and then mixed with syrup to produce a drink or dessert thought to have cooling (yin) properties, which makes it typically consumed during hot weather. The jelly itself has a slight bitter taste, a light iodine lavender flavor, and is a translucent black.