When you pour sparkling beer into a mug or glass, a high layer of white foam forms. With cola or cider, the foam disappears quickly, but with beer, the foam lingers for a long time, almost like a lid.

(Nanowerk News) Anyone who has blown a bubble and seen how quickly it pops has first-hand experience on the major challenge in creating stable foams. At its most basic level, foam is a bunch of ...

Also pouring. There are several Central European style of lager pouring for intentionally increasing the foam head – including one called "milk", where your half‑litre glass is basically only foam.