The perfect pour of any beer from a glass or bottle is all about getting the head just
right for overall taste and visual satisfaction.
Not only does the carbon dioxide in beer head add its own mildly sour taste, but the froth
itself contains a wide variety of delicate flavours that take the form of tiny molecules
that are released and detected in your nose while drinking.
Here are five simple steps to getting it just right -- according to science.
I have an average can of lager and I'm going to be aiming for what many would consider
a perfectly respectable head of one inch, with a slightly domed cap peaking just over
the surface of the glass.
The most important part of science to consider with any pour is all about carbon dioxide
gas and how it can gather together to form bubbles, or froth -- the scientific term for
this is 'nucleation'.
The real trick behind the Perfect Pour is all about controlling the speed at which nucleation
occurs.
In a carbonated beverage like beer, carbon dioxide gas is dissolved in the liquid and
forced to stay there under high pressure from the bottle or can.
When we open the can or bottle that pressure quickly lowers to the normal pressure around
us, and some of the carbon dioxide molecules gathered in big enough groups can force back
the surrounding liquid and escape in the form of a bubble.
This process of 'degasification' is why we observe bubbles forming when we open a bottle
of beer, or any other fizzy drink for that matter!
One thing that helps big enough groups of CO2 molecules to gather together and form
bubbles is having hiding places in which to accumulate away from the liquid pushing in
from all sides.
We call these places 'nucleation sites' and they can be anything from scratches in the
liquid's container, to the surface of tiny particles in the liquid or even other bubbles!
Now we've nailed bubbles, we can go onto the important part -- the scientifically perfect
pour!
Step one is the big choice.
You must select your beverage and a nice clean glass.
If your glass is dirty and scratched this provides lots of nucleation sites for CO2
bubbles to form and can send your froth out of control!
For a very foamy beer, you might want to give your glass a quick rinse with cold water as
this can effectively mask some of those nucleation sites and reduce the number of bubbles forming.
And thus you've controlled the head!
Step two is the tilt.
Hold your glass at a 45 degree angle and gently pour the beer so that there is a small gap
between the interior of the glass and the top of your can or bottle.
The smooth flow of beer ensures that there's less chance of air getting in the liquid and
providing nucleation sites for CO2 bubbles to form.
The 45 degree angle is shallow enough to ensure that the beer flows smoothly down the glass
without making a big 'splash' at the bottom, but steep enough to make sure there is no
'up-splash' when liquid initially hits the glass.
Tilting the glass or can too sharply means that air can enter it as it tries to equalise
the pressure inside.
This can result in lots more nucleation sites and results in a very frothy brew.
Step three, straightening up.
When the beer reaches the lip of the glass, gently halt pouring and start to straighten.
Now a nice headless pour has been achieved we can get ready to intentionally produce
that glorious foam.
Step four, the long pour.
Pour your beer from above into the centre of the glass and watch the creamy head form
until it just bows up over the lip of the glass.
The long pour incorporates air into the beer and allows plenty of nucleation sites for
CO2 bubbles to form.
Those bubbles gather together and bring with them lots of stabilising molecules from inside
the beer to form a perfect and relatively long lasting foam.
Step five, don't lose your head!
Whether you like it or not, your beer head is contributing many delicate flavours to
the overall taste of your beer.
So instead of sipping take measured mouthfuls to ensure you don't slurp away all that carefully
constructed foam and ruin the steady release of aromas as you drink.
All beer heads are unstable which means they will gradually disappear as the bubbles burst.
In order to maintain them and that steady release of beery aromas, many manufacturers
have included laser etched nucleation sites on the bottom of their glasses which ensures
a nice steady release of bubbles throughout your pint experience.
Remember that every beer is different so some may need more or less straight and tilted
pouring to achieve the desired effect.
The important point to remember is that you should enjoy with company and drink as responsibly
as possible.
Cheers!