We’ve all been there once. You’re with friends, it’s all fun and games, you start to pour a beer and someone screams “Nooo! Not like that!” – but it’s too late. Disaster strikes and the glass is half-full of foam. It’s too late to save the beer, it’s just a lot of foam now. Well luckily for you, we’re here to help you pour the best possible beer.
Step 1: The tilt
Every good pour has to start with the glass tilted at 45 degrees. Hold it like this and fill the beer halfway or a bit more.
Step 2: The straightening
After the glass is about 60% full, straighten it and allow some foam to form. Generally, it’s considered that the ideal beer should have about two fingers of foam on the top of the glass – not more. Of course, this can greatly depend on the type of beer.
I wish there was more to say about the pouring itself, but that’s basically how it goes. Now, let’s move onto the more interesting part – why the tilting of the glass is so important and what’s it got to do with foam.
Step 3: The science
Anyone can pour a beer, it’s really no big deal – but not anyone knows the science behind it. It goes like this.
Much like sodas, beer has a lot of carbon dioxide (CO2) in it, it’s what makes it fizzy. When you open a can or a bottle of beer, some of it escapes creating the very familiar sound, but most is still trapped inside the beer. Being a light gas, CO2 wants to escape the beer but it can’t and it needs a little help. The molecules need some space to create bubbles through which they can escape the beer – these spots are called nucleation sites.
Nucleation sites assist the physical separation of solid, liquid, and gas. They are necessary because individual molecules attempting to separate themselves from the beer don’t have enough weight to overcome the viscosity. Several of them need to get together in order to accomplish this. Anything can be a nucleation site – a fiber, dust, a bump – but most commonly in beer, nucleation sites are pockets of air.
When you’re pouring a beer directly, without tilting the glass, you’re helping the CO2 molecules find a nucleation site on the air pockets at the bottom of the glass. You’re basically forcing the air in yourself, by pouring the beer. When you tilt the glass, much more CO2 gets trapped in the beer and less of it escapes in the form of foam.