Understanding the tasting of champagne and other sparkling wines from a scientific perspective.

From uncorking the bottle to the bursting of bubbles in the glass, the science behind the tasting of champagne and other sparkling wine is both traditional and at the forefront of modern developments. The strong interaction between the various parameters at play in a bottle and in a glass of sparkling wine has been the subject of study for around two decades. Indeed, sparkling wine tasting is often seen as the pinnacle of glamor and frivolity for most people, but it should also be considered as a fantastic playground for chemists and physicists to explore the subtle science behind this centuries-old drink, whose prestige today goes well beyond the borders of Champagne and France. This article offers an overview of the physicochemical processes that mark a tasting of champagne or sparkling wine in the broad sense, from the cork popping out of the bottleneck to the formation and bursting of bubbles in your glass, including the choice of the glass and how to serve and drink the wine correctly.

Losses of Yeast-Fermented Carbon Dioxide during Prolonged Champagne Aging: Yes, the Bottle Size Does Matter!

When it comes to champagne tasting, dissolved CO2 is a key compound responsible for the very much sought-after effervescence in glasses. Nevertheless, the slow decrease of dissolved CO2 during prolonged aging of the most prestigious cuvees raises the issue of how long champagne can age before it becomes unable to form CO2 bubbles during tasting. Measurements of dissolved CO2 concentrations were done on a collection of 13 successive champagne vintages stored in standard 75 cL bottles and 150 cL magnums showing prolonged aging ranging from 25 to 47 years. The vintages elaborated in magnums were found to retain their dissolved CO2 much more efficiently during prolonged aging than the same vintages elaborated in standard bottles. A multivariable exponential decay-type model was proposed for the theoretical time-dependent concentration of dissolved CO2 and the subsequent CO2 pressure in the sealed bottles during champagne aging. The CO2 mass transfer coefficient through the crown caps used to seal champagne bottles prior to the 2000s was thus approached in situ with a global average value of K ≈ 7 × 10-13 m3 s-1. Moreover, the shelf-life of a champagne bottle was examined in view of its ability to still produce CO2 bubbles in a tasting glass. A formula was proposed to estimate the shelf-life of a bottle having experienced prolonged aging, which combines the various relevant parameters at play, including the geometric parameters of the bottle. Increasing the bottle size is found to tremendously increase its capacity to preserve dissolved CO2 and therefore the bubbling capacity of champagne during tasting. For the very first time, a long time-series dataset combined with a multivariable model indicates that the bottle size plays a crucial role on the progressive decay of dissolved CO2 experienced by champagne during aging.

Densities, Viscosities, Thermal Expansivities, and Isothermal Compressibilities of Carbonated Hydroalcoholic Solutions for Applications in Sparkling Beverages.

Densities, viscosities, isothermal compressibilities, and thermal expansivities of carbonated hydroalcoholic solutions relevant for sparkling beverages are evaluated by molecular dynamics simulations as a function of temperature and alcoholic degree. They are compared with available experimental data, among which new measurements of densities and viscosities are performed in that respect. The OPC water model seems to yield the most accurate results, and the choice of CO2 model has little influence on the results. Theoretical densities obtained with the OPC model typically deviate by ∼2 kg m-3 from experimental data. At low alcoholic degrees (<9% EtOH vol), experimental viscosities lie in between theoretical values derived from the Stokes-Einstein formula and the calculation of transverse current autocorrelation functions, but at higher alcoholic degrees (≥9% EtOH vol), the Stokes-Einstein relation leads to viscosities in quantitative agreement with experiments. Isothermal compressibilities estimated with a fluctuation formula roughly extend from 0.40 to 0.49 GPa-1 in close agreement with the experimental range of values. However, thermal expansivities are found to significantly overestimate experimental data, a behavior that is partly attributed to the low temperature of maximum density of the OPC model. Despite this discrepancy, our molecular model seems to be suitable for describing several transport and thermodynamic properties of carbonated hydroalcoholic solutions. It could therefore serve as a starting point to build more realistic models for carbonated beverages, from fizzy drinks to sparkling wines.

An Infrared Laser Sensor for Monitoring Gas-Phase CO2 in the Headspace of Champagne Glasses under Wine Swirling Conditions.

In wine tasting, tasters commonly swirl their glasses before inhaling the headspace above the wine. However, the consequences of wine swirling on the chemical gaseous headspace inhaled by tasters are barely known. In champagne or sparkling wine tasting, starting from the pouring step, gas-phase carbon dioxide (CO2) is the main gaseous species that progressively invades the glass headspace. We report the development of a homemade orbital shaker to replicate wine swirling and the upgrade of a diode laser sensor (DLS) dedicated to monitoring gas-phase CO2 in the headspace of champagne glasses under swirling conditions. We conduct a first overview of gas-phase CO2 monitoring in the headspace of a champagne glass, starting from the pouring step and continuing for the next 5 min, with several 5 s swirling steps to replicate the natural orbital movement of champagne tasters. The first results show a sudden drop in the CO2 concentration in the glass headspace, probably triggered by the liquid wave traveling along the glass wall following the action of swirling the glass.

Does the Temperature of the prise de mousse Affect the Effervescence and the Foam of Sparkling Wines?

The persistence of effervescence and foam collar during a Champagne or sparkling wine tasting constitute one, among others, specific consumer preference for these products. Many different factors related to the product or to the tasting conditions might influence their behavior in the glass. However, the underlying factor behind the fizziness of these wines involves a second in-bottle alcoholic fermentation, also well known as the prise de mousse. The aim of this study was to assess whether a low temperature (13 °C) or a high temperature (20 °C) during the in-bottle fermentation might have an impact on the effervescence and the foaming properties (i.e., collar height and bubble size) of three French sparkling wines (a Crémant de Loire and two Champagne wines), under standard tasting conditions. Our results showed that sparkling wines elaborated at 13 °C and served in standard tasting conditions (i.e., 100 mL, 18 °C) had better ability to keep the dissolved CO2 (between 0.09 and 0.30 g/L) in the liquid phase than those elaborated at 20 °C (with P < 0.05). Most interestingly, we also observed, for the Crémant de Loire and for one Champagne wine, that the lower the temperature of the prise de mousse, the smaller (with P < 0.05) the bubbles in the foam collar throughout the wine tasting.

Recent Progress in the Analytical Chemistry of Champagne and Sparkling Wines.

The strong interplay between the various parameters at play in a bottle and in a glass of champagne or sparkling wine has been the subject of study for about two decades. After a brief overview of the history of champagne and sparkling wines, this article presents the key steps involved in the traditional method leading to the production of premium modern-day sparkling wines, with a specific focus on quantification of the dissolved CO2 found in the sealed bottles and in a glass. Moreover, a review of the literature on the various chemical and instrumental approaches used in the analysis of dissolved and gaseous CO2, effervescence, foam, and volatile organic compounds is reported.

Toward In Silico Prediction of CO2 Diffusion in Champagne Wines.

Carbon dioxide diffusion is the main physical process behind the formation and growth of bubbles in sparkling wines, especially champagne wines. By approximating brut-labeled champagnes as carbonated hydroalcoholic solutions, molecular dynamics (MD) simulations are carried out with six rigid water models and three CO2 models to evaluate CO2 diffusion coefficients. MD simulations are little sensitive to the CO2 model but proper water modeling is essential to reproduce experimental measurements. A satisfactory agreement with nuclear magnetic resonance (NMR) data is only reached at all temperatures for simulations based on the OPC and TIP4P/2005 water models; the similar efficiency of these two models is attributed to their common properties such as low mixture enthalpy, same number of hydrogen bonds, alike water tetrahedrality, and multipole values. Correcting CO2 diffusion coefficients to take into account their system-size dependence does not significantly alter the quality of the results. Estimates of viscosities deduced from the Stokes-Einstein formula are found in excellent agreement with viscometry on brut-labeled champagnes, while theoretical densities tend to underestimate experimental values. OPC and TIP4P/2005 water models appear to be choice water models to investigate CO2 solvation and transport properties in carbonated hydroalcoholic mixtures and should be the best candidates for any MD simulations concerning wines, spirits, or multicomponent mixtures with alike chemical composition.

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

The diffusion of carbon dioxide (CO2) and ethanol (EtOH) is a fundamental transport process behind the formation and growth of CO2 bubbles in sparkling beverages and the release of organoleptic compounds at the liquid free surface. In the present study, CO2 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 CO2. 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.

How Many CO2 Bubbles in a Glass of Beer?

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).

How Does Gas-Phase CO2 Evolve in the Headspace of Champagne Glasses?

The chemical space perceived by a consumer of champagne or other sparkling wines is progressively modified all along tasting. Real-time monitoring of gas-phase CO2 concentration was performed, through a CO2-diode laser sensor, along a two-dimensional array of nine points in the headspace of three types of glasses poured with champagne. Two original glasses with distinct headspace volumes were compared with the standard INAO tasting glass. For each of the three glass types, a kind of temperature-dependent CO2 fingerprint was revealed and discussed as a function of the glass geometry and headspace volume. Moreover, a simple model was developed, which considers the rate of decrease of the concentration of gas-phase CO2 in the headspace of a glass after the pouring process as being mainly ruled by natural air convection in ambient air. The timescale which controls the rate of decrease of gas-phase CO2 was found to highly depend on the ratio of the headspace volume to the open aperture of the glass.

Combined Experimental and CFD Approach of Two-Phase Flow Driven by Low Thermal Gradients in Wine Tanks: Application to Light Lees Resuspension.

In winemaking, clarification and stabilization are the processes by which insoluble matter suspended in the wine (called lees) is removed before bottling. The light lees represent 2-4% of the total wine volume. Under certain circumstances, resuspension of lees may occur. The resuspension of lees has been attributed to temperature variations between the wine stored in tanks and the environment of the cellar. From in situ, laboratory-scale studies involving laser tomography techniques, it was shown that low (positive or negative) thermal gradients between a wine tank containing light lees and its external environment induce mass transfer by natural convection. To extrapolate these findings to full-scale tanks, an Eulerian-Eulerian multiphase CFD model was applied to simulate the two-phase flow behavior as a function of temperature variations on a 24-h cycle. Numerical temperature and time-dependent flow patterns of both wine and lees confirm that low thermal gradients induce sufficient fluid energy to resuspend the lees, thus showing that the laboratory results can be extrapolated to full-scale tanks.

Computational Fluid Dynamics (CFD) as a Tool for Investigating Self-Organized Ascending Bubble-Driven Flow Patterns in Champagne Glasses.

Champagne glasses are subjected to complex ascending bubble-driven flow patterns, which are believed to enhance the release of volatile organic compounds in the headspace above the glasses. Based on the Eulerian-Lagrangian approach, computational fluid dynamics (CFD) was used in order to examine how a column of ascending bubbles nucleated at the bottom of a classical champagne glass can drive self-organized flow patterns in the champagne bulk and at the air/champagne interface. Firstly, results from two-dimensional (2D) axisymmetric simulations were compared with a set of experimental data conducted through particle image velocimetry (PIV). Secondly, a three-dimensional (3D) model was developed by using the conventional volume-of-fluid (VOF) multiphase method to resolve the interface between the mixture's phases (wine-air). In complete accordance with several experimental observations conducted through laser tomography and PIV techniques, CFD revealed a very complex flow composed of surface eddies interacting with a toroidal flow that develops around the ascending bubble column.

Under-expanded supersonic CO2 freezing jets during champagne cork popping.

During champagne cork popping, the CO2/H2O gas mixture initially under pressure in the bottleneck freely expands into ambient air and experiences adiabatic cooling. A comparison between the condensation phenomena accompanying cork popping from bottles stored at 20° and 30°C was made. The initial headspace-to-ambient-pressure ratio much exceeded the critical ratio needed for the gas mixture to reach Mach 1, thus forming under-expanded supersonic CO2 freezing jets expelled from the throat of the bottlenecks. It was emphasized that, after adiabatic cooling and with a saturation ratio for gas-phase CO2 about twice higher for the bottles stored at 30°C, dry ice CO2 clusters grow bigger and reach the critical size needed to achieve the Mie scattering of light. Moreover, during the very first millisecond following cork popping, evanescent normal shock waves (or Mach disks) were unveiled in the jets, until the reservoir-to-ambient-pressure ratio goes below a critical ratio.

Carbon Dioxide in Bottled Carbonated Waters and Subsequent Bubble Nucleation under Standard Tasting Condition.

Experimental and theoretical developments, including gas-liquid thermodynamics and bubble nucleation, were made relevant to the conditioning and service of three various commercial carbonated bottled waters holding different levels of dissolved carbon dioxide comprised between about 3 g L-1 and 7 g L-1. The strong dependence in temperature of the partial pressure of gas-phase CO2 found within the three batches of bottled carbonated waters was determined. Moreover, in a glass of carbonated water, the process by which the diffusion of dissolved CO2 in tiny immersed gas pockets enabled heterogeneous bubble nucleation was formalized, including every pertinent parameter at play. From this assessment, the minimum level of dissolved CO2 below which bubble nucleation becomes thermodynamically impossible was determined and found to strongly decrease by increasing the water temperature and size of the gas pockets acting as bubble nucleation sites. Accordingly, the total number of bubbles likely to form in a single glass of sparkling water was theoretically derived to decipher the role played by various key parameters. Most interestingly, for a given level of dissolved CO2, the theoretical number of bubbles likely to form in a glass was found to increase by increasing the water temperature.

Monitoring gas-phase CO2 in the headspace of champagne glasses through combined diode laser spectrometry and micro-gas chromatography analysis.

During Champagne or sparkling wine tasting, gas-phase CO2 and volatile organic compounds invade the headspace above glasses, thus progressively modifying the chemical space perceived by the consumer. Gas-phase CO2 in excess can even cause a very unpleasant tingling sensation perturbing both ortho- and retronasal olfactory perception. Monitoring as accurately as possible the level of gas-phase CO2 above glasses is therefore a challenge of importance aimed at better understanding the close relationship between the release of CO2 and a collection of various tasting parameters. Here, the concentration of CO2 found in the headspace of champagne glasses served under multivariate conditions was accurately monitored, all along the 10 min following pouring, through a new combined approach by a CO2-Diode Laser Sensor and micro-gas chromatography. Our results show the strong impact of various tasting conditions (volume dispensed, intensity of effervescence, and glass shape) on the release of gas-phase CO2 above the champagne surface.

Unveiling CO2 heterogeneous freezing plumes during champagne cork popping.

Cork popping from clear transparent bottles of champagne stored at different temperatures (namely, 6, 12, and 20 °C) was filmed through high-speed video imaging in the visible light spectrum. During the cork popping process, a plume mainly composed of gaseous CO2 with traces of water vapour freely expands out of the bottleneck through ambient air. Most interestingly, for the bottles stored at 20 °C, the characteristic grey-white cloud of fog classically observed above the bottlenecks of champagne stored at lower temperatures simply disappeared. It is replaced by a more evanescent plume, surprisingly blue, starting from the bottleneck. We suggest that heterogeneous freezing of CO2 occurs on ice water clusters homogeneously nucleated in the bottlenecks, depending on the saturation ratio experienced by gas-phase CO2 after adiabatic expansion (indeed highly bottle temperature dependent). Moreover, and as observed for the bottles stored at 20 °C, we show that the freezing of only a small portion of all the available CO2 is able to pump the energy released through adiabatic expansion, thus completely inhibiting the condensation of water vapour found in air packages adjacent to the gas volume gushing out of the bottleneck.

Evaporation of droplets in a Champagne wine aerosol.

In a single glass of champagne about a million bubbles nucleate on the wall and rise towards the surface. When these bubbles reach the surface and rupture, they project a multitude of tiny droplets in the form of a particular aerosol holding a concentrate of wine aromas. Based on the model experiment of a single bubble bursting in idealized champagnes, the key features of the champagne aerosol are identified. In particular, we show that film drops, critical in sea spray for example, are here nonexistent. We then demonstrate that compared to a still wine, champagne fizz drastically enhances the transfer of liquid into the atmosphere. There, conditions on bubble radius and wine viscosity that optimize aerosol evaporation are provided. These results pave the way towards the fine tuning of flavor release during sparkling wine tasting, a major issue for the sparkling wine industry.

Modeling the Losses of Dissolved CO(2) from Laser-Etched Champagne Glasses.

Under standard champagne tasting conditions, the complex interplay between the level of dissolved CO2 found in champagne, its temperature, the glass shape, and the bubbling rate definitely impacts champagne tasting by modifying the neuro-physicochemical mechanisms responsible for aroma release and flavor perception. On the basis of theoretical principles combining heterogeneous bubble nucleation, ascending bubble dynamics, and mass transfer equations, a global model is proposed, depending on various parameters of both the wine and the glass itself, which quantitatively provides the progressive losses of dissolved CO2 from laser-etched champagne glasses. The question of champagne temperature was closely examined, and its role on the modeled losses of dissolved CO2 was corroborated by a set of experimental data.

Chemical messages in 170-year-old champagne bottles from the Baltic Sea: Revealing tastes from the past.

Archaeochemistry as the application of the most recent analytical techniques to ancient samples now provides an unprecedented understanding of human culture throughout history. In this paper, we report on a multiplatform analytical investigation of 170-y-old champagne bottles found in a shipwreck at the bottom of the Baltic Sea, which provides insight into winemaking practices used at the time. Organic spectroscopy-based nontargeted metabolomics and metallomics give access to the detailed composition of these wines, revealing, for instance, unexpected chemical characteristics in terms of small ion, sugar, and acid contents as well as markers of barrel aging and Maillard reaction products. The distinct aroma composition of these ancient champagne samples, first revealed during tasting sessions, was later confirmed using state-of-the-art aroma analysis techniques. After 170 y of deep sea aging in close-to-perfect conditions, these sleeping champagne bottles awoke to tell us a chapter of the story of winemaking and to reveal their extraordinary archaeometabolome and elemental diversity in the form of chemical signatures related to each individual step of champagne production.

It's time to pop a cork on champagne's proteome!

Champagne is a world-renowned French sparkling wine, which undergoes many steps (fermentation, aging …) for its elaboration. Various compounds might evolve during this winemaking process and thus modify its final quality. Here, we report the first proteome analysis of two standard commercial Champagne wines, using the powerful Combinatorial Peptide Ligand Library (CPLL) technique. Indeed, wine proteins are present in small amounts but they are key compounds, likely to impact on both foam quality and aroma behavior. Forty-three unique gene products were retrieved in a single-varietal champagne and a blended champagne. Several proteins from Vitis vinifera together with seven yeast proteins were undoubtedly identified in these Champagne wines. BIOLOGICAL SIGNIFICANCE: The main advantage of CPLLs was the detection of low abundance proteins despite the absence of purification or pre-concentration step. It is an important fact to take into account, since Champagne wines generally contain a low amount of proteins (5-10mg/L) that implies to usually concentrate wine proteins before 1D or 2D electrophoresis. Most Champagne proteins are grape and yeast glycoproteins which are considered as good foam "promoters". Some of these proteins might also interact with wine aromas, and thus contribute to the overall quality of Champagne wines. This article is part of a Special Issue entitled: Proteomics of non-model organisms.