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Speaker 1: Welcome to brain stuff. From how stuff works, Hey, brain stuff,

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Speaker 1: Lauren vocal bomb. Here. Pour a soda into a glass

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Speaker 1: and it will foam, But those tiny bubbles quickly die down. Beer,

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Speaker 1: on the other hand, will form a foamy head that

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Speaker 1: sticks around long after it's been poured. Both are carbonated

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Speaker 1: and poured from a bottle, can, or fountain. So why

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Speaker 1: does beer form ahead but soda doesn't. There's a lot

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Speaker 1: going on in that foamy beer head, from the delicate

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Speaker 1: interaction of gas and protein to alcohol content. Beer is complex,

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Speaker 1: and we don't just mean the flavor. Like it or

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Speaker 1: hate it. Beer foam is a preview of what you're

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Speaker 1: about to imbibe. As each beer bubble releases an aroma,

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Speaker 1: the scent begins to influence your perception of the beverage

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Speaker 1: and wet your anticipation as you prepare to drink it. Plus,

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Speaker 1: a dense head of foam can make a beer feel

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Speaker 1: more creamy and flavorful. Beer is, in fact the only

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Speaker 1: alcoholic beverage that will form and maintain ahead of foam.

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Speaker 1: The formation of this foam, also known as nucleation, involves

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Speaker 1: a complex reaction of proteins. This includes large protein molecules

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Speaker 1: and their smaller cousins polypeptides. One protein specific to barley malt,

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Speaker 1: which is used in the brewing of beer, is where

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Speaker 1: the closer look. It's called lipid transfer protein one, or

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Speaker 1: LTP one, and it has a serious aversion to water.

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Speaker 1: To escape the wet stuff, it will use a bubble

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Speaker 1: of carbon dioxide as a life preserver. Thankfully, for LTP one,

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Speaker 1: there are a lot of life preservers because CO two

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Speaker 1: is produced in abundance during the fermentation of beer and

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Speaker 1: may also be introduced during bottling. As LTP one clings

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Speaker 1: to the carbon dioxide and rises to the surface, it

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Speaker 1: will form a protective coating around the bubble that makes

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Speaker 1: it more difficult to pop. This helps beer maintain its

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Speaker 1: head far longer than a soda or hard cider, but

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Speaker 1: it's not the only factor at work. Additional hydrophobic polypeptides

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Speaker 1: bond with compounds that enter the beer courtesy of the

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Speaker 1: hops that beer usually contains. The ops iso alpha acids,

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Speaker 1: further lend stability to the phone. Even with the potential

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Speaker 1: for all these bubbles to stick around, a foamy head

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Speaker 1: isn't a sure thing. A beer has a sweet spot.

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Speaker 1: An alcohol content of about five percent too high or

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Speaker 1: too low, and the foam will dissipate more quickly. Keep

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Speaker 1: in mind that beer foam would be nothing without a

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Speaker 1: glass in which to reach its full potential. The next

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Speaker 1: time you drink a frothy glass of ale, take a

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Speaker 1: closer look at that vessel. Are there nearly imperceptible scratches

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Speaker 1: on the inside of the glass? Is there a brand

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Speaker 1: logo etched into the glass's interior, perhaps at the bottom.

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Speaker 1: This interruption of the flat surface creates a nucleation site,

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Speaker 1: a series of cracks and scratches designed to encourage bubbles

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Speaker 1: to continue to form and rise. These special adaptations, paired

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Speaker 1: with beer's penchant for foam, mean its head will outlast

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Speaker 1: sodas no matter how it's poured. Today's episode was written

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Speaker 1: by Lauriel Dove and produced by Tyler Clang. For more

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Speaker 1: this and lots of other bubbly topics, visit our home planet,

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Speaker 1: how Stuff Works dot com.