Q. Shalom Aleichem Harav
If a protein powder is rice based, does that make the shake mezonos?
Shkoyach

A. Shulchan Aruch (208: 6) rules that a thin cereal mixture of light consistency that one drinks as a liquid, the brocho is shehakol. See Vessen Brocho (p. 532), that this applies even when one eats the mixture with a spoon.
Horav Shlomo Miller’s Shlit’a opinion is that the brocho on the liquid shake is shehakol, being similar to spirits and beer created from grain.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a