Ordering a Guinness on draft takes longer than most other beers. Part of the reason is the gas used to carbonate it – nitrogen. William Lee, a professor of Industrial Mathematics at the University of Huddersfield, in a study funded by the Science Foundation Ireland, discovered that the specially designed Guinness pint glass causes the bubbles to sink and increases the wait time for the beer to settle.
Following a transcript of the video.
Narrator: You’ve been pouring Guinness all wrong, but don’t worry, it’s not your fault, it’s Guinness’.
Order a pint of the black stout in a pub, and you’re going to notice something very strange about the beer: Its bubbles are sinking! But wait. Bubbles are supposed to rise all the time! Is Guinness defying the laws of physics? Not exactly.
Every Guinness is supposed to be poured into a specially crafted tulip glass. But that glass is designed to manipulate the bubbles in the beer to turn the pour into a performance, making you wait longer than you need to. But let’s back up a bit and explain something about how the bubbles in a Guinness stout are different than most other beers.
William Lee: So the weird thing about stout beers is the bubbles inside; they’re very small.
Narrator: This is William Lee. He’s a professor of Industrial Mathematics at the University of Huddersfield, in the UK, and his research has found a problem with the traditional Guinness glass pint. Most beers are carbonated using carbon dioxide, but Guinness bubbles are filled with nitrogen. This is what gives the stout that iconic silky texture in your mouth and distinctive creamy head resting above the dark beer. When you look closely at a Guinness while it’s settling, the bubbles are actually falling instead of rising.
Lee: Whereas in the beer that has carbon-dioxide bubbles, the bubbles are bigger. So they are less affected by flow and the bubbles go up no matter what.
Narrator: If bubbles are supposed to float up, what exactly is causing Guinness bubbles to do something crazy and sink? Lee and his team devised a number of equations to explain this peculiar behaviour.
Lee: So, we’ve got a very simple model, which just describes the motion of the bubbles rising under gravity and fluid sinking when it’s more dense. And that was enough to predict sinking bubbles.
Narrator: These equations might not look so simple to the untrained eye. They helped Lee identify a problem with the specially designed Guinness glass.
Lee: Well, the sinking bubbles – that has very much to do with the shape of the glass. So as the bubbles go up, they’re moving away from the sloping walls. And behind they’re leaving just beer, which is denser. So you’ve got dense beer besides the walls, and of course dense beer sinks. And as it sinks it carries the bubbles with it. So that’s why you see the sinking bubbles in Guinness with the small bubbles, which get carried down by the currents.
Narrator: And here is where Guinness has exploited this sinking-bubble phenomenon, making it part of its branded pouring presentation. The pour is marketed by Guinness as a six-step process including a special pint glass, a correct angle of pouring, and even a midway waiting period in which the beer separates before the pint is topped off. It has become a time-honored ritual in pubs around the world. A bulk of that time is the settling. But this time period is as much about marketing as it is the physics. You may be waiting longer than you would for another beer, but that’s by design.
Commercial: It can’t be rushed. As we say, “Good things come to those who wait.”
Narrator: Now you might think that the beer flowing into the glass is causing a current that affects the bubbles. And you’d be right, but it’s small, and not even factored into Lee’s models. The bigger effect comes from the tulip shape of the Guinness glass once you set it down.
Lee: So we think that afterwards, when things are more or less still, a second effect affecting the currents is going on. And that’s essentially the bubbles trying to rise, but depending on the shape of the walls, that’s going to cause bubbles to either separate from the beer or accumulate. And once you have that, you have variations in density. And, of course, variations in density are going to cause flow.
Narrator: So if the Guinness glass isn’t the perfect glass for a pint of Guinness, what is?
Lee: Unfortunately, I think that the ideal glass is going to be shaped like a giant cocktail glass. Sloping walls going straight out. But basically gigantic and looking very strange. So the ideal glass would be kind of martini-shaped.
Narrator: Wait a minute. A martini glass?! I mean, just look at it – just the idea is absurd. Yet it’s almost remarkable how quickly it settles. But this still leaves you with a choice of waiting or using something ridiculous. Will Lee’s work help solve this?
Lee: So I’m hoping that somewhere in between the standard pint glass and the giant martini glass there’s something where settling happens a bit quicker then it happens at the moment, but that doesn’t look totally ridiculous, something that beer drinkers might actually use.
Narrator: For now, what you choose depends on a marketing tradition versus getting to drink your beer faster. What’s your choice?
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