Question

Why do bubbles rise to the surface of Guinness slower than they rise to the surface of a light beer? (The beers are of very similar viscosity).If you poured the two beers very carefully into the same glass what would you expect to see?

Answer 1

Guinness is a nitrogenated beer which means contains nitrogen gas along with CO2 gas. In fact amount of CO2 is Guinness is much lower than that of in regular beer. If regular beer contains 100% CO2 then amount of CO2 in Guinness would be arpund 30-40% and the remaining 60-70% is N2 gas

Under a given pressure, CO2 gas is much more soluble than N2 and therefore concentration of CO2 would be more in beer.

When Beer is poured gas gets trapped within the gas pockets already present in the beer, and as more and more gas gets trapped , bubble grows in size and finally detaches from the bottom or side of the glass and rises to the top. This is particlarly seen in regular beers. We can see large bubbles of CO2 getting formed and the beer foams quickly.

But when there is higher % of N2 in a beer which already have lower solubility , there is not much time left for the bubble to grow in size, so in case of nitrogenated beers, we see smaller bubbles which often travel slowly to the top. The main reason behind this is lower solubility of gas.

When we pour two beers into the same glass, we would expect the regular beer to foam up quickly and give a huge frothy layer whereas guinness would rise up slowly and smoothly.