Pushed, not poured: the tiny holes in an espresso machine
A few days ago I got stuck on what I thought was a simple question. When you pull a shot of espresso, the hot water comes out of a metal plate full of small holes, the shower screen, and lands on the coffee as a gentle, even rain. How does water get through holes that small so neatly? I had a picture in my head for this: a bathroom shower, water sitting up top, gravity doing the work, the holes letting it dribble through. Both halves of that picture were wrong, and the real answer is a lot more interesting. ...