A few years ago I decided to get certified as a Cicerone, the beer version of a sommelier. During my studies for the title, I learned what constitutes a “Beer Clean” glass. It’s honestly something I’d never thought of before. A clean glass is a clean glass, right? Wrong….

Source: http://lifehacker.com/how-to-quickly-tell-if-your-beer-glass-is-really-clean-1798734099