This week’s question was asked by a relative at a wedding reception.
QUESTION: Why are there bubbles in my beer?
ANSWER: You can encounter a lot of science by watching a glass of beer, just so long as you’re not crying in your beer! Tiny bubbles of carbon dioxide form on microscopic particles in the beer. The bubbles accumulate more carbon dioxide gas as they rise and become bigger. They also acquire more buoyancy and hence rise faster. A bubble-string climbing from the bottom never appears uniform. Bubbles are smaller and closely spaced at the bottom of the glass while those near the top are bigger and farther apart.
Adding a little salt to the drink provides many bubble-forming sites, called nucleation sites. The foam, or head, of the drink is simply an accumulation of the bubbles that have risen. Brewers fatten their foam by adding protein thickeners to produce sturdy bubbles that are small and have thick walls and won’t break as easily.
One particular protein naturally found in barley is Lipid Transfer Protein 1 (LTP1), and it plays a large role in a beer’s foam. There are numerous other variables that impact the formation of the foam head on beer: the types of hops, the temperature or climate that produced the barley, the cleanliness of the beer glass, the alcohol content and the amount of nitrogen.
Some beer glasses are etched on the bottom to create additional nucleation sites. Bubbles cling to the etching and accumulate until they’re buoyant enough to break free and rise to the top of the beer, replenishing the head.
Oddly enough, what is on a beer drinker’s lips has an effect. Waxes in lipstick or chapstick can block protein interactions and poke holes in a bubble’s protective protein skin, killing beer foam. Fats from foods that are on a beer guzzler’s lips can kill bubbles.
Years ago, Leinenkugel’s Brewery in Chippewa Falls sold a six-pack of bock beer that came with a pencil. A poured glass of bock had such a thick foam head on the beer that a pencil would stand up in it. Their commercial claimed that their bock beer “is so hearty and headstrong you can stick a pencil in it! So take a moment to savor that deep caramel color, the distinctive, creamy taste. Availability: January – March.”
A few years ago, we were on a bus tour of the Benelux (Belgium, Netherlands, Luxembourg) countries. One stop was a Trappist brewery located within the walls of the Abbey of Notre-Dame, in the southeast region of Belgium. A document written by the abbot in 1628 directly refers to the making and consumption of beer and wine by the monks. These days the brewery produces Orval beer. The brewery provides funds to continue the restoration of the Notre-Dame Abbey.
The guide told our tour group that Orval beer “is the best beer in the world. It is so good that we feed it to our horses, and what comes out is Heineken.” We all had a good laugh on that one. Heineken, sold in a green bottle or can with a bright red star, is a big seller in the Benelux countries.
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Larry Scheckel is a retired Tomah High School physics teacher.