As Wikipedia states beer head (also head or collar), is the frothy foam on top of beer which is produced by bubbles of gas, typically carbon dioxide, rising to the surface. Beer head doesn’t affect the constitution of the beverage, but it alters its taste.
There are all kinds of beer enthusiasts all over the world, some of them love bigger foams on their drink but the others consider it as if the usually white collar is just an unnecessary obstacle that helps the tapster to skimp its beer, even though the beer head is not just beautiful but it’s the sign of quality as well. It indicates that if the drink consists proper amount of carbon dioxide and shows that if the wort was made from good ingredients with fair proportions.
The durability of the head relates to the dry matter content of the beer and its protein content too – the richer the beverage, its head is going to be durable and harder.
During tapping the formation of the foam is important in countries such as Belgium (where the glass is half full of foam).
In the UK there are huge differences between regions. In London and South East, the foam is superfluous but on the contrary, in Northern England, some beer head is desirable in the beer mugs.
Actually, there are three different types of tapping techniques (and three kinds of beer/foam ratios) and using them you can drink the exact same beer with various taste and texture. The most common tapping style called na dvakra. Using this method the foam is produced at the end of tapping so the beverage keeps the carbon dioxides and remains fresh and crispy. In case of the hladinka techinque, the foam is the first in the mug and the beer is tapped below that. Thus we get our drink softer and more flavorful. When we tap only the head then we get the mlíkó, a milk-colored, thick, pretty much durable beer head that surprisingly tastes like sweetish malt but the hop flavor also appears in the background.
Last but not at least the hygiene is also significant. Glass surfaces retain oil from the skin and when these oils come in contact with beer there is a significant reduction in the amount of head. For reaching beautiful foam it’s crucial to dry the glass after washing because water in the mug prevents excitement of the gas and makes the beer flat. (Tapping tip: in course of Belgian witbiers you can control the abundant head with the previously mentioned strategy – pour your beer into a wet glass.)