Answer Your Foam
Nobody has asked me anything specific lately, so I decided to lecture everybody about beer foam. As a brewer, nothing gets me riled up like when people demand beer liquid right up to the brim of a glass, it’s only a half ounce more beer people and you are missing the best part of the experience. We work hard to get that foam there and it should be appreciated. Think of the creamy head on a newly poured beer as a key, a key that unlocks the aroma door and allows you to smell and taste all complex flavors that inhabit your glass.
Foam 101 (Skip if bored easily)
I’ll apologize in advance for throwing out terms like coalescence and disproportionation but foam gets me all excited and I can’t help myself. Foam is formed by the breakout of CO2 due to mechanical input (i.e. pouring, or some jackass shaking your beer up). This provides the bubbles and the energy. The other half of the emulsion is the liquid. The liquid is what forms the bubble walls and is made up of bridges formed by the interactions of hydrophobic proteins from the malt, metal ions, and iso-alpha acids. These are the same alpha acids that we get from hops that impart the bitter flavor in beer and that is why the foam always tastes more bitter that the beer itself.
There are five separate processes (bubble formation, beading, drainage/evaporation, coalescence, and disproportionation) and many more attributes within the beer that affect its formation and stability. Bubble formation is obvious, although the size and consistency of that size will play a role in how lasting the foam is. This is why nitrogen dispensed beers have such creamy head because the size of the bubbles is small. Beading is the constant replenishment of foam through gas breakout. Drainage and evaporation is the loss of liquid and therefore the thinning of the bubble walls. This leads to coalescence and diproportionation. These are the collapse of a bubble into another and gas diffusion from one bubble to another, respectively. The process, recipe, and even the cleanliness of your glassware can affect all these factors, oh and mustaches are foam negative (I know the ladies like them but think of the beer).
More than a Feeling
Now that you all know that the head is an integral part of the beer experience and how much we care about it, the next time you order a pint you’ll demand at least a fingers worth of head and if you order a bottle, tell your server to pour it straight down the middle and leave the bottle. Enjoy its aroma, feel and taste and know it is meant to be there.