Ask the expert – what is a pint?

In the UK, the volume of a pint is defined as 568ml (20 Imperial fluid ounces) of liquid. This measurement includes the frothy layer of foam on top of the beer, commonly known as a beer’s head. The head consists of gas bubbles – mainly carbon dioxide (CO2) – surrounded by hydrophobic proteins deriving from barley and wheat, alongside polypeptides bonded with hop alpha-acids. Given enough time, the foam will dissipate, reverting to a liquid, hence why the head is included as part of a pint’s quantification....