2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Chemists theoretically and experimentally analyzed the formation of bubbles of carbon dioxide in beer at parameters typical of commercial brands of the drink. It turned out that in a glass filled with 250 milliliters of lager with 5% alcohol, cooled to six degrees Celsius, about hundreds of thousands of CO2 bubbles are formed at a liquid level of about 10 centimeters. The article was published in the ASC Omega magazine.
Today, lager (bottom-fermented beer) is the most affordable and widely consumed type of beer. As a rule, bottled and canned drinks of this type are under the pressure of gaseous CO2, which means (due to the exchange of molecules between the liquid and gaseous phases) they also contain a certain amount of this substance dissolved in the liquid itself.
The presence of CO2 affects the rate of formation and growth of gas bubbles in the liquid, and with this, the taste and aroma of beer. In recent years, scientists have already investigated similar effects for other drinks - for example, they estimated the number of bubbles in a glass of champagne, found out how they help to reveal the aroma of the latter, and determined the minimum concentration of CO2 at which you can still distinguish its flavor in sparkling wine. However, the details of the behavior of carbon dioxide in beer remained unexplored until recently.
Gérard Liger-Belair and Clara Cilindre of the University of Champagne-Ardenne theoretically linked the number of bubbles in commercial bottled beer to beverage parameters, and then estimated this value using experimental measurements.
The authors took advantage of the fact that in a closed bottle of commercial beer, carbon dioxide is concentrated in a relatively small volume (about five milliliters compared to 250 milliliters of the beer itself) and can be described by the equation of state of an ideal gas, and the equilibrium concentration of dissolved CO2 in a drink is directly proportional to its partial pressure over liquid according to Henry's Law. It turned out that at a temperature of 0-20 degrees Celsius, the equilibrium partial pressure in a closed bottle is about 2-3 bar, while when the cap is removed, it (together with the equilibrium concentration) drops almost ten thousand times - to typical atmospheric values (about 0.4 millibars).
A sharp change in the equilibrium concentration leads to the fact that dissolved CO2 tends to leave the drink - it diffuses through the interface with air, and bubbles form in the volume of the liquid. In this case, the real concentration tends to equilibrium with a delay - the formation of bubbles is suppressed by the energy barrier. To overcome this barrier, gas cavities must exist in the liquid phase (for example, near the walls of a vessel) with a radius of curvature greater than the critical value, which increases with a decrease in the concentration of CO2 in the liquid. Because of this, over time, it becomes more difficult for bubbles to form, and the process weakens until the formation of bubbles finally ceases to be thermodynamically possible.
An image of microscopic irregularities on the glass surface that aid in the formation of bubbles. Scale bar length - 100 micrometers
Connecting the concentration at which the formation of bubbles ends, with the surface tension at the interface between liquid and gas, ambient pressure and Henry's constant, the scientists expressed the total number of bubbles formed (for the entire time the dissolved CO2 content fell) through the characteristics of the drink (viscosity, density, volume, the level of the surface of the liquid in the glass and the initial concentration of the solution), as well as the temperature and pressure at which the experiment is carried out.
For the measurements, the researchers used a commercial lager in 250 milliliter bottles with five percent alcohol and a CO2 concentration of about 5.5 grams per liter. Before the experiments, the drink was stored for at least two days in a refrigerator at a temperature of 6 degrees Celsius.
In the course of the experiments, the authors carefully (avoiding excessive turbulence and excessive foaming, which were not taken into account in the theoretical model) poured the contents of the bottles into four identical half-liter glasses, previously washed with distilled water and dried at a temperature of 60 degrees Celsius. Scientists took measurements four times (for different bottles of beer) and averaged the results, and the density and viscosity were determined only after degassing the drink.
It turned out that with a liquid level of 8.9 centimeters and a critical radius of curvature of gas cavities of 1-10 micrometers, from two hundred thousand to one million CO2 bubbles are formed in a lager glass.
Comparison of theoretical estimates of the total number of carbon dioxide bubbles in beer (blue curve) and champagne (red curve) under similar conditions depending on the critical radius of curvature of gas cavities.
It is noted that approximately the same number of bubbles occurs in a glass with 100 milliliters of champagne at a similar temperature and liquid level (10 degrees Celsius and 7.4 centimeters). In beer, however, a sharper dependence on the critical radius of curvature of gas cavities is observed - with a radius of 1 micrometer, approximately half as many bubbles are formed in it than in champagne, and at 10 micrometers, already twice as many.
Recently, beer has become the subject of research in other areas of science. So, in May last year, archaeologists proposed to identify traces of beer production by the microstructure of cereal grains, in 2018 scientists predicted an increase in the price of a drink due to global warming, and in 2016 they found that the subjective perception of beer taste can be improved with the help of music.