Do bubbles in Guinness go
Frequently Asked Questions
is a list of questions
that we have been asked. If you don't see an answer elsewhere on
the site, it may be here.
- Why is this effect important?
- Is the shape of the glass important?
- Is the gas important?
- Method of pouring?
- What about viscosity?
- How did you get draught Guinness in the laboratory?
- What did you do with all the Guinness after
- What's a widget?
- Do the model simulations and experiments
this effect important?
effects are important
because they tell us about how liquids flow,
for example, in industrial
processes and manufacture. Liquid flows are important in a wide
range of circumstances ranging from medicine to oceanography.
Drinks and food manufacturers also
considerable amount of effort and money to make their products
appealing: easy pouring and a nice head is one of the aspects that
we consumers look for in our beer.
shape of the glass important?
shape of the glass is not that
important. We obtained similar results in curved and straight
glasses. The pattern of flow will be different in the different
shaped glasses, but not to the extent that would remove the effect.
Is the gas important?
it is. See detailed answer to "Does it
happen in any liquid?".
Method of pouring?
way the Guinness is poured is not crucial.
Despite the angle/position of pouring, it is the upward flow of bubbles
in the center of the glass that causes the circulation: see "Why do the bubbles go down?". If you pour it
so that there are hardly any bubbles produced, then you will not see
What about viscosity?
viscous liquids flow more slowly (e.g., syrup). The viscosity of
Guinness will be only slightly
different than that of water, but not much. Certainly not enough
to affect the movement of the bubbles that can be seen.
in the lab?
might wonder how we got a
good supply of Guinness in the lab. The experiments took many
days, and it would have been difficult to set up all the equipment in
the local bar! Fortunately, the Guinness company makes their
draught stout available in cans,
using a special patented pouring
device (the "widget") that creates all those
Although we tried refrigeration before using them, condensation on the
caused difficulties, so we used the cans at room temperature.
happened to the Guinness you used?
we poured it away.
Don't be sad - you might never have seen any of the pictures if we had
actually drunk any of it during filming!
What's a widget?
widget is the patented device (also called a "smoothifier") in the
special draught-flow can or bottle
that contains a small amount of Guinness and nitrogen gas at very high
pressure. If you shake one of the
cans you can hear it rattle. Why not open a can up and have a
look? When the can/bottle is opened, the gas is suddenly released
through one (or more) pin-sized holes. This creates a lot of
Do the simulations and experiments agree?
and conclusions agree very well with the simulations
carried out by Prof. Clive Fletcher and his group. The sinking
bubbles in the experiments seem to be slightly larger than in the
simulations. The experiments also suggest that the bubbles inside (that
go up) seem to be nearer to the walls in the experiments. An
interesting detailed comparison would come from looking just below the
head, where we see almost equal numbers of bubbles going up and down.
(c) 2004 Alexander & Zare