Why Does Beer Foam Last Longer Than Soda Foam?

Beer and soda both form sudsy bubbles when you pour them, so why does soda's foam dissipate while beer's forms a head? Learn about foam physics in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff. From how stuff works, Hey, brain stuff,
Lauren vocal bomb. Here. Pour a soda into a glass
and it will foam, But those tiny bubbles quickly die down. Beer,
on the other hand, will form a foamy head that
sticks around long after it's been poured. Both are carbonated
and poured from a bottle, can, or fountain. So why

(00:22):
does beer form ahead but soda doesn't. There's a lot
going on in that foamy beer head, from the delicate
interaction of gas and protein to alcohol content. Beer is complex,
and we don't just mean the flavor. Like it or
hate it. Beer foam is a preview of what you're
about to imbibe. As each beer bubble releases an aroma,

(00:43):
the scent begins to influence your perception of the beverage
and wet your anticipation as you prepare to drink it. Plus,
a dense head of foam can make a beer feel
more creamy and flavorful. Beer is, in fact the only
alcoholic beverage that will form and maintain ahead of foam.
The formation of this foam, also known as nucleation, involves
a complex reaction of proteins. This includes large protein molecules

(01:06):
and their smaller cousins polypeptides. One protein specific to barley malt,
which is used in the brewing of beer, is where
the closer look. It's called lipid transfer protein one, or
LTP one, and it has a serious aversion to water.
To escape the wet stuff, it will use a bubble
of carbon dioxide as a life preserver. Thankfully, for LTP one,

(01:28):
there are a lot of life preservers because CO two
is produced in abundance during the fermentation of beer and
may also be introduced during bottling. As LTP one clings
to the carbon dioxide and rises to the surface, it
will form a protective coating around the bubble that makes
it more difficult to pop. This helps beer maintain its
head far longer than a soda or hard cider, but

(01:49):
it's not the only factor at work. Additional hydrophobic polypeptides
bond with compounds that enter the beer courtesy of the
hops that beer usually contains. The ops iso alpha acids,
further lend stability to the phone. Even with the potential
for all these bubbles to stick around, a foamy head
isn't a sure thing. A beer has a sweet spot.

(02:11):
An alcohol content of about five percent too high or
too low, and the foam will dissipate more quickly. Keep
in mind that beer foam would be nothing without a
glass in which to reach its full potential. The next
time you drink a frothy glass of ale, take a
closer look at that vessel. Are there nearly imperceptible scratches
on the inside of the glass? Is there a brand
logo etched into the glass's interior, perhaps at the bottom.

(02:34):
This interruption of the flat surface creates a nucleation site,
a series of cracks and scratches designed to encourage bubbles
to continue to form and rise. These special adaptations, paired
with beer's penchant for foam, mean its head will outlast
sodas no matter how it's poured. Today's episode was written

(02:57):
by Lauriel Dove and produced by Tyler Clang. For more
this and lots of other bubbly topics, visit our home planet,
how Stuff Works dot com.