Why do the bubbles in a Guinness sink instead of rising?
In partnership with Guinness
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You've probably already noticed, but in a pint of Guinness, the bubbles don't rise, like in other drinks… They sink! And that's due to several factors. First, unlike other beers, Guinness also contains nitrogen in addition to carbon dioxide. That's why the bubbles are so small!
And the fact that nitrogen bubbles are small makes them less affected by buoyancy. As a reminder, buoyancy states that any object immersed in a fluid experiences an upward force equal to the weight of the fluid displaced.
So nitrogen bubbles CAN sink. But… they don't necessarily do so everywhere!
For example, in a Guinness glass, which flares out at the sides, the bubbles rise through the center and then descend along the sides, in the wider area, which therefore has fewer bubbles. From the outside, we only see the ones that are descending!
But if Guinness obeys the laws of physics, its serving also follows very specific rules:
To serve a Guinness, bartenders must adhere to several rules:
The serving temperature must be between 5 and 7°C
The glass must be tilted at a 45° angle
The pour must be done in two stages: first, pour three-quarters full, up to the top of the rim, let it rest to allow the foam to form, then finish by topping up the glass! This process must take exactly 119.5 seconds.
It is this pouring technique that gives it such a creamy texture, in which you can observe the famous Guinness Cascade!