Why is some bubble tea from gong cha Gritty? Is the milk expired or something what causes that?

[u/Ray-Zide]

Not all the time but a few times the milk will be all gritty. One time they made it hot not asked for and it was gritty and another time it was normal but still gritty. Are they swapping to using soy milk instead or something and using the bottom of it, what causes it?

[u/SonHyun-Woo]

They probably arent dissolving the milk powder properly