Unveiling Carbon Dioxide and Ethanol Diffusion in Carbonated Water-Ethanol Mixtures by Molecular Dynamics Simulations.

Mohamed Ahmed Khaireh,Gérard Liger-Belair,Marie Angot,David A Bonhommeau,Clara Cilindre

doi:10.3390/molecules26061711

Abstract

The diffusion of carbon dioxide (CO) and ethanol (EtOH) is a fundamental transport process behind the formation and growth of CO bubbles in sparkling beverages and the release of organoleptic compounds at the liquid free surface. In the present study, CO and EtOH diffusion coefficients are computed from molecular dynamics (MD) simulations and compared with experimental values derived from the Stokes-Einstein (SE) relation on the basis of viscometry experiments and hydrodynamic radii deduced from former nuclear magnetic resonance (NMR) measurements. These diffusion coefficients steadily increase with temperature and decrease as the concentration of ethanol rises. The agreement between theory and experiment is suitable for CO. Theoretical EtOH diffusion coefficients tend to overestimate slightly experimental values, although the agreement can be improved by changing the hydrodynamic radius used to evaluate experimental diffusion coefficients. This apparent disagreement should not rely on limitations of the MD simulations nor on the approximations made to evaluate theoretical diffusion coefficients. Improvement of the molecular models, as well as additional NMR measurements on sparkling beverages at several temperatures and ethanol concentrations, would help solve this issue.

Highlights

IntroductionDissolved carbon dioxide (CO2 ) is obviously the gaseous species responsible for the sparkle in every sparkling beverage
They increase regularly as the alcoholic degree increases and the temperature decreases. These results are in agreement with former measurements carried out on carbonated hydroalcoholic solutions with ethanol concentrations representative of brut-labeled champagnes
Viscosities from the literature obtained for hydroalcoholic solutions and brut-labeled champagnes are indicated [33]

Summary

Introduction

Dissolved carbon dioxide (CO2 ) is obviously the gaseous species responsible for the sparkle in every sparkling beverage. For example, dissolved CO2 results from a second in-bottle fermentation process promoted by adding yeasts and sugar in a still base wine stored in thick-walled glass bottles hermetically sealed with a crown cap or a cork stopper [4]. In bottled or canned beers, dissolved CO2 is the result of a natural fermentation process [5,6]. In carbonated soft drinks (and in some cheaper sparkling wines and sparkling waters) carbonation is rather undertaken by forcing exogenous gas-phase CO2 to dissolve into still soft drinks, and by conditioning them in cans or in bottles most often sealed with crown or screw caps [1]

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