You don’t usually see this in the US. This drink is both sour and sweet and sends a chill down your spin – a mild version of the liquid Wasabi drink, if you can imagine it. Not spicy though! This is made from the concentrate of the pickled plum or ume. In Chinese, it’s 酸梅.
If you are ever in the country and brave enough to try it, go to any Seven Eleven and look for them at the bottom refrigerated shelf, hidden next to the other unusual drinks Taiwan has to offer. Enjoy!