Foamy Beer? Grab a Magnet

Actually magnets is for home brewers – see the last paragraph for other tricks.

Few sights at a bar are more deflating than a bottle of beer overflowing with foam. This overfoaming, called gushing, arises when fungi infect the barley grains in beer’s malt base. The microorganisms latch onto barley with surface proteins called hydrophobins. During the brewing process, these hydrophobins can attract carbon dioxide molecules produced by the mashed barley as it ferments, making the beer far too bubbly. Brewers try to tamp down the gushing by adding hops extract, an antifoaming agent that binds to the proteins first. Now, food scientists in Belgium have hit upon a technological solution: magnets.

Source: No more foamy beer, thanks to magnets

A higher level of hop oil (or pretty much any vegetable oil, really) will reduce foaming. But that is an academic concern, because you can’t alter the hop levels without affecting the flavour. A brewer will perfect the taste/aroma/color/texture/etc. of a beer before they even start thinking about practical concerns such as blow-off. Which is fine because there are already solutions for blow-off that don’t involve reformulating your recipe.

What is the science behind contributing factors to overfoaming?  Carbon dioxide (CO2) solubility decreases with increasing temperature.  As the dissociation constant of water increases, the extra hydrogen ions push out the carbon dioxide molecules.   In addition, gaseous solubility decreasing with increasing temperature causes the energy of the CO2 molecule to exceed the solvation energy.  Translation: the warmer the fridge is, the more foam will come out. Things you can do:

  • Chill the beer more
  • Cool the outside of the glass with cold tap water
  • Pour a slow stream of beer down the side of the glass (not directly to the bottom). This chills the path of the beer and you are less likely to foam. If you pour directly to the bottom, it’ll just push out.

Standard disclaimer: Alcohol is addictive, laden with empty calories, and socially complex. Be careful™.