How Many CO2 Bubbles in a Glass of Beer?

Abstract

The number of bubbles likely to form in a glass of beer is the result of the fine interplay between dissolved CO₂, tiny particles or glass imperfections acting as bubble nucleation sites, and ascending bubble dynamics. Experimental and theoretical developments about the thermodynamic equilibrium of dissolved and gas-phase carbon dioxide (CO₂) were made relevant to the bottling and service of a commercial lager beer, with 5% alcohol by volume and a concentration of dissolved CO₂ close to 5.5 g L^-1. The critical radius and the subsequent critical concentration of dissolved CO₂ needed to trigger heterogeneous nucleation of CO₂ bubbles from microcrevices once the beer was dispensed in a glass were derived. The subsequent total number of CO₂ bubbles likely to form in a single glass of beer was theoretically approached as a function of the various key parameters under standard tasting conditions. The present results with the lager beer were compared with previous sets of data measured with a standard commercial Champagne wine (with 12.5% alcohol by volume and a concentration of dissolved CO₂ close to 11 g L^-1).

Figure 1

Scheme of a capped beer bottle exemplifying the thermodynamic equilibrium experienced by dissolved and gas-phase CO₂ between the liquid phase and the gaseous headspace under the crown cap (courtesy of K dapple-designer/Pixabay).

Figure 2

Pressure of gas-phase CO₂ which prevails within the 250 mL sealed lager beer bottles in the range of temperature between 0 and 20 °C. For comparison purposes, the temperature-dependent pressure of gas-phase CO₂ found in a standard 750 mL corked bottle of champagne appears in red. Reproduced from ref (7) with permission from Springer Nature.

Figure 3

Temperature dependence of the critical radius of curvature r* required for bubble nucleation in a glass, immediately after serving, for both the lager beer and champagne, in the range of temperatures between 0 and 20 °C.

Figure 4

Two micrographs showing the network of microcrevices responsible for nonclassical heterogeneous bubble nucleation in laser-etched glasses (bar = 100 μm) (a) and a particle with a micrometric gas cavity trapped inside, acting as a bubble nucleation site in a glass poured with champagne (bar = 20 μm) (b).

Figure 5

Critical concentration of dissolved CO₂c_L^* required for bubble nucleation in a glass as a function of the radius of curvature r of pre-existing gas cavities acting as bubble nucleation sites, for both the lager beer and champagne dispensed at 6 and 10 °C, respectively.

Figure 6

High-speed photographs showing ascending and growing bubbles in a glass of beer (a), as compared with bubbles ascending and growing in a flute poured with champagne (b) (bar = 1 mm).

Figure 7

Theoretical total number of CO₂ bubbles likely to nucleate in a glass poured with 250 mL of beer at 6 °C (with a beer level of 8.9 cm) plotted versus the radius of curvature of gas cavities acting as bubble nucleation sites at the bottom of the glass (see inset). For comparison, the theoretical total number of CO₂ bubbles likely to form in a flute poured with 100 mL of a standard champagne dispensed at 10 °C (with a level of champagne of 7.4 cm) appears in red. Reprinted (Adapted) with permission from ref (28). Copyright 2014 American Chemical Society.