You probably didn't recently rewatch the whole show like I did!
It's one of the affectations she picked up while living in the Vulcan colony on earth. Part of her arc is she's not a particularly "good" Vulcan and the tea is one of the little tells.
Some stuff they brew through an insanely convoluted ritual. If asked, they will tell you how super logical it is to practice such rituals on every occasion possible and that it is completely rational without so much as a flinch. Stonefaced delusional bastards