Nucleation is the name of the process of forming bubbles. In brewing, this process of nucleation is what eventually results in the materialisation of beer foam, or the Head on a Beer.
The head consists of proteins that are acted on by the hops, the yeast, and the carbonation (usually carbon dioxide) and can have a complexity that adds to the taste of the beer which is the reason so many brewers spend much time and energy trying to create the perfect amount of bubble.
The bitter Iso-alpha acids (IAAs) that derive from hops when cross-linked with the hydrophobic polypeptides of the chosen brewing grain (wheat, barley etc) results in a foam that is denser and more stable, eventually forming a head of foam that better “clings” to the glass. The special foam-forming ingredient in beer, resultant of the beer’s proteins, is called albumin. This albumin forms complex bonds with the bitter hop compound, which in turn makes it easy for bubbles to stick around. These albumins have a high rate of what’s known as “hydrophobicity”, meaning they don’t like water, so in order to help alleviate their predicament of being trapped in water, they grab a hold of a bubble of C02 and then rise to the surface of the beer alongside the C02 bubble. These proteins form coatings on the bubbles and this helps stabilise the integrity of the foam once the bubbles reach the surface of the beer.
But what does all this mean for the taste of the beer? Well, that’s the simple part really. And the not so simple part!
Firstly, we must understand that often when it comes to identifying a specific “taste”, an individual is often actually experiencing a nasal “odour”, and not a taste at all. Our senses of smell and taste are intricately interwoven, and often it’s impossible to tell the difference between the two senses. The premise with a beer head, therefore, is that the foam will bring the beverage odour compounds right to the surface of the beer and thus open up your nose so you are able to experience the full-flavours of the beer.
Whilst there is no “exact” guidance as to what the size a head of beer should be, in our experience we prefer the beer foam to be about a half-inch to an inch. We find that this is the optimum level of foam that sticks around long enough to ensure we get that full-flavour experience.
An excellent informative read LP, thank you! I will certainly show my next beer a little more consideration!🍺🍺🍺