Guinness is one of the most interesting beers on the planet. Not only does this stout have a unique taste and ABV, it also possesses one, simple peculiarity—the bubbles. They seemingly sink rather than float.
Believe it or not, there has been a lot of scientific research to determine the cause of the submerging bubbles. Former-professor Dr. William Lee is leading the majority of the research—he once taught Applied Mathematics at the University of Limerick.
When Dr. Lee noticed the strange phenomenon, he was determined to find out why. His first hypothesis was the shape of a beer glass and the chemical properties of nitrogen were the cause.
Firstly, Guinness is one of the few beers with nitrogen synthetically added during the brewing process. Compared to carbon dioxide bubbles, nitrogen’s have less buoyancy, so it’s not very difficult to pull them down.
The illustration of a tennis ball and a basketball in a pool is usually used to bring the point across. The tennis ball represents a nitrogen bubble and the basketball a carbon-dioxide bubble. Which one will be easier to hold down in the water? Obviously the tennis ball. The tennis ball or nitrogen bubble is more dense thus less buoyant.
So what exactly in Guinness is pulling the bubbles down?
Dr. William Lee and collaborators conducted an experiment to find out and published it in a series of papers in 2011 and 2013. In the experiment, he poured Guinness into a normal pint glass, which has a narrow base. He then poured Guinness into a non-traditional pint glass, which had a wide base. In the normal pint glass, the bubbles at the side of the glass sank to the bottom. But in the non-traditional pint glass, the bubbles at the side of the glass rose. Dr. Lee concluded “the shape of a normal pint glass creates areas of low, bubble density along the edges of the glass and areas of high, bubble density in the middle of the glass.”
Dr. Lee and his collaborators documented the entire experiment in a five-page document which you can read here.
In order to figure out why Guinness bubbles sink, it’s crucial to understand how the shape of the glass affects the bubbles. In a normal pint glass, the bubbles pull away from the sides of the glass and create a cluster in the center. This cluster causes the glass’s center to have a very high, bubble density. With some (relative) force, these bubbles then float to the top of the glass—it doesn’t end there though. The bubbles at the top are then pulled back down “around the column in order to fill the low bubble density areas along the sides and bottom.”
But this piece of Dr. Lee’s research wasn’t just done to find out why the bubbles sink—there’s a bigger reason behind it. In the paper, he wrote, “Is the shape of the Guinness pint glass the most efficient possible, or could the settling time [AKA the time you have to wait before you drink the beer after pouring] be significantly reduced by some other, possibly non-axisymmetric, shape of pint glass?”
Ultimately, the research was done to figure out how we can drink Guinness faster.