bitter

A bunch of my 40-odd year old nightshift co slackers were trying to figure out which parts of their tongues were sensitive to the supposed four main tastes: sweet, sour, bitter, salty. They couldn't think up anything for the bitter category that didn't fit better under sour, so I muttered »alum« into a magazine. Headslapping astonishment ensued. One of them told me I had no business even knowing what alum is and that he could often sense I was an Old Soul.