Why do bubbles in Guinness sink?

Why do bubbles in Guinness sink?

The simplistic answer is nitrogen bubbles plus a glass that is wider at the top than the bottom. Which is most glasses. Including any popular variety of pint glass. CO2 bubbles will not do the trick. Guinness, unlike a normal beer, has nitrogen in addition to CO2. I do not know if other stouts also contain nitrogen.

The study the flow of nitrogen bubbles and liquid in a Guinness Gravity Pint Glass. A Guinness Gravity Pint Glass has slightly curved sides. This is the kind of pint glass, with the Guinness logo, that Guinness sells (or if you are lucky, gives away)
[quote][url=https://www.guinnesswebstore.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/g/u/guinness1_1.jpg]Picture of Guinness Gravity Pint Glass[/url]
[/quote]
The bubbles in Guinness also move downward in a simple pint glass
[quote][url=http://ts4.mm.bing.net/th?id=JN.PaTyFtcq5lyydahf9zmfbg]Picture of Simple Pint Glass[/url]
[/quote] as you have observed. Unless you were always too consumed with drinking Guinness to notice the bubbles.

The study also modelled what the authors call an Anti-Pint Glass. The Anti-Pint Glass is the Guinness Gravity Pint Glass turned upside down. Except that the horizontal part is on the now-wide bottom. And the now-narrow top is open -- so you can pour beer into it. The study also modelled what the authors call an Anti-Pint Glass. The Anti-Pint Glass is the Guinness Gravity Pint Glass turned upside down. Except that the vertical part is on the now-wide bottom and the the now-narrow top is open -- so you can pour beer into it. The authors did not manufacture an Anti-Pint Glass. They just modelled it with a software program.

In an Anti-Pint Glass the bubbles in Guinness go the way you would expect in a liquid -- up. Basically, if the walls of the glass come between the Guinness and the floor (as in a Pint Glass) the bubbles in Guinness travel downward. If the walls of the glass come between the Guinness and the ceiling (as in  an Anti-Pint Glass) the bubbles in Guinness travel upward. You can see both effects at once by pouring Guinness into a glass cylinder and tilting it. Or you can watch the video where the authors have kindly done it for you.
[quote][url=http://arxiv.org/src/1205.5233v1/anc/tilted_cylinder.avi]Tilted Cylinder of Guinness[/url] (Video ~1 MB)[/quote]
If you are ambitious you can read the study
[quote][url=http://arxiv.org/pdf/1205.5233v1]Why do bubbles in Guinness sink?[/url] (PDF ~250 KB)[/quote]
The study is four pages, including charts. There are a few formulas. But most of the text is understandable to the layman. But it is an academic paper, Not a transcript of Mr. Wizard.