Using "the hell out of" as an adverb in this sentence is just a colorful way of saying: How to make coffee that will impress your guests "very much." You can scare the hell out of somebody, beat the hell out of somebody, get the hell out of town,etc. There are a lot of colorful idioms using "the hell out of" as an adverbial phrase. You can even make up your own! For example: He answered the hell out of that question!