Yeast can be a noun, verb or adjective and even a pronoun in some context for example referring to a friend or colleague as "yeaster". First as a noun "yeast" describes any liquid that contains live bacteria or fungi which turn that liquid into an alcoholic beverage, the percentage of "yeast" can be found normally on the back of the bottle, for example a standard yeast is around 4.5 - 6% yeast, as a noun there is also another meaning which is synonymous with "absolutely shit faced" or "shteamin", for example "I'm going to get yeasted tonight at the gaff with the geezers". As a verb, infinitive "to yeast" simply is used to talk about the action of consuming yeast, in the present simple tense: I yeast with my mate at the local. Finally as an adjective we add a "y" to the end of yeast to describe nouns, anything that is described as "yeasty" has a strong aroma or flavour that reminds the subject of pure yeast, for example " I went back to my room after being on holiday for 2 weeks and it was so yeasty"
I got so fucking yeasted last night I was sick put of my left eye socket, god that was some strong yeast, let's do the same again tonight, what do you think yeaster?