Kinetics and stability of the mixing flow patterns found in champagne glasses as determined by laser...

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Kinetics and stability of the mixing flow patterns found inchampagne glasses as determined by laser tomographytechniques: likely impact on champagne tasting

Gerard Liger-Belaira,∗, Fabien Beaumontb, Marie-Anne Vialatte c, Sandrine Jegoua,Philippe Jeandeta, Guillaume Polidorib

a Laboratoire d’Oenologie et Chimie Appliquee, UPRES EA 2069, UFR Sciences Exactes et Naturelles, Universite de ReimsChampagne-Ardenne, BP 1039, 51687 Reims, Cedex 02, Franceb Laboratoire de Thermomecanique, UTAP EA 2069, UFR Sciences Exactes et Naturelles, Universite de Reims Champagne-Ardenne, BP1039, 51687 Reims, Cedex 02, Francec Centre de Recherche Appliquee et de Transfert d’Expertise (CREATE), rue du Quartier de Cavalerie, 62500 Saint Omer, France

a r t i c l e i n f o

Article history:

Received 28 August 2007

Received in revised form

23 October 2007

Accepted 25 October 2007

Published on line 12 November 2007

Keywords:

Champagne

Sparkling wines

a b s t r a c t

Laser tomography techniques were used in order to make visible the flow patterns induced

by ascending bubbles in flutes poured with champagne. The stability of flow patterns was

investigated in flutes showing natural (without any specific surface treatment) as well as

artificial effervescence (i.e., engraved at their bottom), all along the first 15 min after pouring.

Engravement conditions were found to strongly influence the kinetics and the stability with

time of the mixing flow phenomena found in champagne glasses.

© 2007 Elsevier B.V. All rights reserved.

Carbonated beverages

Bubble nucleation

Effervescence

Laser tomography

to better illustrate, detect, understand and finally control

Champagne tasting

1. Introduction

From a strictly chemical point of view, champagne andsparkling wines are multicomponent hydroalcoholic systemssupersaturated with CO2-dissolved gas molecules (formedtogether with ethanol during the fermentation process). As
soon as a bottle of champagne or sparkling wine is uncorked,the progressive release of CO2-dissolved gas molecules isresponsible for bubble formation, the so-called effervescence
∗ Corresponding author. Tel.: +33 3 26 91 86 14; fax: +33 3 26 91 86 14.E-mail address: [email protected] (G. Liger-Belair).

0003-2670/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.aca.2007.10.054

process. Actually, champagne and sparkling wine tastingmainly differs from still non-effervescent wine tasting dueto the presence of bubbles continuously rising throughthe liquid medium. This is the reason why considerableefforts have been conducted the last few years in order

each and every parameter involved in the bubbling process(for a review, see for example reference [1] and referencestherein).

mailto:[email protected]

dx.doi.org/10.1016/j.aca.2007.10.054

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related to bubbles arising from scratches intentionally doneby the glassmaker to promote effervescence or eventuallyreplace a deficit of natural effervescence. Nevertheless, effer-vescence produced from scratches intentionally done by the

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In weakly supersaturated liquids such as carbonated bever-ges in general and champagne in particular, bubble formationnd growing require preexisting gas cavities with radii of cur-ature large enough to overcome the nucleation energy barriernd grow freely [2,3]. Jones et al. made a classification of theroad range of nucleation likely to be encountered in liquidsupersaturated with dissolved gas [2]. Bubble formation fromreexisting gas cavities larger than the critical size is referreds non-classical heterogeneous bubble nucleation (type IVubble nucleation, following their nomenclature). Generallypeaking, effervescence in a glass of champagne or sparklingine may have two distinct origins. It can be “natural” or “arti-cial”.

On one hand, natural effervescence is related to the bub-ling process from a glass which has not experienced anypecific surface treatment. Closer inspection of such glasses
oured with champagne and sparkling wines revealed thatost of the bubble nucleation sites were found to be located
n preexisting gas cavities trapped inside hollow and roughly

ig. 1 – Cellulose fiber acting as a bubble nucleation site onhe wall of a flute poured with champagne (bar = 1 mm).

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cylindrical cellulose-fiber-made structures on the order of 100-�m long with a cavity mouth of several micrometers [4,5] (seeFig. 1). Fibers probably adhere on the flute wall due to electro-static forces (especially if the glass or the flute is vigorouslywiped by a towel). Natural effervescence may also arise frompreexisting gas cavities trapped inside the microscopic defectsof tartrate crystals precipitated on the glass wall (especiallyif the glass is rinsed with tap water). Therefore, there is asubstantial variation concerning the “natural” effervescencebetween flutes depending on how the flute was cleaned andhow and where it was left before serving.

On the other hand, artificial effervescence in a glass is

Fig. 2 – At the bottom of this flute, on its axis of symmetry,the glassmaker has engraved a small ring (done withadjoining laser beam impacts). Effervescence is promotedfrom these “artificial” microscratches into the form of acharacteristic and easy recognizable vertical bubblescolumn (bar = 1 mm).

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�

Fig. 4 – Detail of the gas/liquid interface at the free surfaceof a flute poured with champagne. Because the velocityfield close to the gas/liquid interface directly controls thediffusion process of a given compound (through the Fick’s

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glassmaker (by sandblast or laser engraving) does not resem-ble that arising from tiny cellulose fibers. A rendering of suchmicroscratches releasing bubbles at the bottom of a cham-pagne flute is displayed in Fig. 2. It is worth noting that therepetitive bubbling process arising from artificial bubble nucle-ation is much more vigorous and chaotic than the bubblingprocess from tiny cellulose fibers. Glasses engraved at theirbottom are thus indeed easily recognizable, with a character-istic bubble column rising on their axis of symmetry.

During champagne or sparkling wine tasting, consumerscertainly pay attention to the continuous flow of ascendingbubbles (often even before smelling and tasting the wine).Ascending bubbles are indeed visually appealing, but their roleis suspected to go far beyond the sole aesthetical point of view.Actually, at the bubble scale, the lower part of a rising bubble isa low-pressure area which literally attracts the fluid moleculesaround (see Fig. 3). A rising bubble is thus able to drain somefluid along its path toward the free surface. The huge num-ber of bubbles released from the numerous nucleation sitesfound in a typical champagne glass (of order of several hun-dreds of bubbles released per second during the first minutesof champagne tasting) is therefore able to set the whole liq-uid bulk in motion. Very recently, by using laser tomographytechniques, it was demonstrated that ascending bubbles actas so many swirling motion generators in champagne glasses[6]. By vigorously and continuously mixing the liquid mediumall along tasting, ascending bubbles are indeed suspected toplay a major role in flavor and gas release. Actually, the flavorand gas release from the wine interface is a diffusion processwhich is therefore ruled by the so-called Fick’s law expressed
as follows:
Ji = ci�V − Di

�∇ci (1)

Fig. 3 – A rising bubble is able to drain some fluid along itspath through the champagne bulk.

law), this parameter, neglected up to now, has to beaccurately determined.

where �Ji, �V, ci, �∇ci, and Di are the flux of a given compound ithrough the gas/liquid interface, the velocity of the liquid flow,the bulk concentration of the given compound, the concentra-tion gradients of the given compound close to the interface,and the diffusion coefficient of the given compound in thechampagne bulk, respectively (see Fig. 4). It is clear from Eq.(1) that both gas discharge and flavor release are highly fluidvelocities-dependent through the parameter �V. Therefore, tobetter approach the kinetics of flavor and gas release fromglasses poured with champagne and sparkling wines, thevelocity field close to the wine interface needs to be betterknown all along the tasting process. The main experimentalchallenge is consequently to make visible the champagne flowpatterns, which are obviously invisible to the naked eye.

In the present paper, classical flow visualization techniqueswere used once again in order to make the fluid motion visible.
The stability of the mixing flow patterns in flutes poured withchampagne (showing natural and artificial effervescence) wasinvestigated during the first 15 min of a typical champagnetasting.
Fig. 5 – Photograph of the optical workbench used tocapture the champagne flow patterns; the laser sheetboundaries are made visible by solid blue lines.

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. Materials and methods

laser tomography technique was used in order to visual-
ze, as accurately as possible, the flow patterns induced byhe continuous flow of ascending bubbles in flutes pouredith champagne. The principle of the experiment is to gen-
rate a 2-mm-thick laser sheet, built from a multi-line argon

ig. 6 – Typical time-sequence showing the flow patterns foundffervescence.

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laser source (INNOVA 70 C-2 W) centered on the 514 nm wave-length. The 2-mm-thick laser sheet crosses the plane ofsymmetry of a champagne flute. But before pouring cham-pagne into the flute, champagne was seeded with tiny and
roughly spherical particles (called Rilsan® particles). Rilsanparticles are polymeric materials which exhibit a high degreeof reflectivity with regard to the laser wavelength and aretherefore able to diffuse the laser light as they cross the 2-
in the plane of symmetry of the flute showing natural

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mm-thick laser sheet. Rilsan particles are neutrally buoyant(75 �m < diameter < 150 �m; � = 1.06 g cm−3). Moreover, Rilsanparticles were found to be completely neutral with regard
to bubble formation (this was definitely a crucial conditionfor the feasibility of the present work). Classical long expo-sure time photography of the laser sheet, with a digital photocamera (Minolta, Dimage 7i), was used in order to follow the
Fig. 7 – Time-sequence showing details of the development of edvarious eddies and vortices which cohabit in the flute showing nrandom distribution of bubble nucleation sites in the flute.

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motion of Rilsan particles, thus freezing the flow patternsinside the fluid section crossed by the laser sheet. Trajectoriesof convection currents in champagne glasses were therefore
made visible by numerous streaks of light left by the Ril-san particles along their path through the laser sheet. Theoptimal volume fraction condition of Rilsan particles in thechampagne bulk was found to be of order of 1.3 × 10−4. A
dies near the champagne free surface. The interplay of theatural effervescence is highly complex and results from the

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hotograph of the optical workbench used to capture thehampagne flow patterns is displayed in Fig. 5. In Fig. 5,he laser sheet boundaries are made visible by solid blue
ines.
A standard commercial champagne wine holding about0 g L−1 of CO2-dissolved molecules was used for this set ofxperiments. Champagne was poured into a standard com-

ig. 8 – Typical time-sequence showing the flow patterns found i

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mercial flute (provided by our partner, the glassmaker ARCInternational). We have tested flutes being engraved or not attheir bottom, thus providing a natural as well as an artificial
effervescence in this flute model. The kinetics of flow pat-terns in both flute models were investigated all along the first15 min which follow the pouring process. Experiments wereperformed at room temperature (20 ± 2 ◦C).
n the plane of symmetry of the flute engraved at its bottom.

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is almost at rest. Therefore, both glass shape and engravementconditions influence the overall characteristics of mixing flowphenomena found in champagne glasses.

Fig. 9 – Flow patterns found in the plane of symmetry of acoupe engraved at its bottom. It can be seen that, as for theflute engraved at its bottom, the rising bubble columnforces the flow patterns into the form of twocounter-rotative vortices close to the glass axis.Nevertheless, in this case, the external periphery of the


3. Results and discussion

3.1. Kinetics of the flow patterns in the flute showingnatural effervescence

In Fig. 6, four successive frames of a typical time-sequenceshowing the flow patterns found in the flute showing natu-ral effervescence are displayed. All along the 15 min whichfollow the pouring process, champagne is found to be mechan-ically mixed by various convection currents, made visible bythe movement of the neutrally buoyant Rilsan particles whichfreeze the fluid motion during the 2 s exposure time of our digi-tal photo camera. It is worth noting that the various convectioncells and eddies found in the flute may change randomly insize and location with time. For example, the time-sequencedisplayed in Fig. 7 presents photographic details of the flowpatterns found in the same champagne flute. Two minutesafter pouring, one can observe the development of two vor-tices close to the free surface, namely a large-scale eddy, calledE, and a secondary counter-clockwise one, called e1. Then,one can observe the displacement and the progressive van-ishment of eddy e1 towards the central axis of symmetry ofthe flute. From the fluid mechanics point of view, this radialmotion causes an adverse pressure gradient area and thedevelopment of a multi-cell system composed of eddies e2,e3 and E at t = 4 min. One notes then a stabilization of this phe-nomenon up to t = 10 min where the main vortex E tends tomove downwards along the wall due the swing of the divid-ing streamline L leading to the saddle point Sp. Of initially 2Dshape, eddy e3 changes towards a 3D spiral shape, inducingthe beginning of a generalized complexification of the flowpatterns.

Therefore, in flutes showing natural effervescence, time-sequences presented in Figs. 6 and 7 illustrate that theconvection currents induced by the flow of ascending bubblesare not at all stable with time. Actually, in a flute showing nat-ural effervescence, bubbles arise from nucleation sites locatedrandomly on the flute’s wall. Furthermore, bubbles may alsoarise from nucleation sites directly found in the liquid bulk(mostly composed of cellulose fibers detached from the wall).These particles immersed in the champagne bulk produceeasily recognizable bubble trains which seem to dance insidethe glass during champagne tasting along their erratic paththrough the liquid medium [7]. The “bubbling environment” istherefore highly random in a flute showing natural efferves-cence. This is the reason why the mixing flow mechanisms,directly induced by the random distribution of bubble nucle-ation sites, are highly complex and not at all stable with timein a flute showing natural effervescence.

3.2. Kinetics of the flow patterns in the flute engravedat its bottom

In Fig. 8, four successive frames of a typical time-sequenceshowing the flow patterns found in the flute engraved at its
bottom are displayed. It is clear that strong differences appearin the flow behavior according to whether the glass has sus-tained or not a specific surface treatment. Actually, due tothe high degree of reflectivity of bubbles with regard to the
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laser wavelength, one clearly observes the formation of therising gas column along the vertical axis of symmetry of theflute (from the treated bottom surface up to the free surface ofchampagne). One can also clearly notice from Fig. 8 that therising bubble column generates two large and well-establishedvortices which are very stable, and last all along the 15 minof a tasting. Actually, because the flute exhibits cylindricalsymmetry around its central axis, the real three-dimensionalstructure of the flow patterns in the engraved flute is that ofa deformed torus. Therefore and contrary to the case of theflute showing natural effervescence, the convection currentsfound within the engraved flute are very stable with time. Themain reason is that the ascending liquid flow generated bythe rising central bubbles column largely exceeds the othercontributions to the liquid flow generated by the likely pres-ence of single bubble trains randomly distributed within theglass. The main convection currents are undoubtedly forcedby this intense and artificial effervescence. Moreover, it isworth noting that, in the case of the engraved champagneflute, the whole domain of the champagne bulk is homoge-neously mixed, with very high values of the average fluidvelocities, all along the 15 min which follow the pouring pro-cess.

Recently, in the case of an engraved champagne coupe (aglass with a shallower bowl and a wider aperture than that ofthe flute), only about half of the liquid medium was found tobe mixed by the flow of ascending bubbles arising from thebottom of the coupe [6] (see Fig. 9). The external periphery ofthe coupe is characterized by a “dead-zone” where champagne

glass is characterized by a dead-zone where thechampagne is almost at rest. It means that, for such awide-brimmed glass, only about half of the liquid bulkparticipates to the champagne mixing process.

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. Conclusions and prospects

aser tomography techniques proved to be a useful tool inrder to make visible the flow patterns in glasses pouredith champagne. It was found that both glass shape and

ngravement conditions influence the kinetics and the sta-ility with time of the mixing flow phenomena found inhampagne glasses. Moreover, because the velocity field ofhe fluid medium strongly depends on both glass shape andngravement conditions, the kinetics of flavor and gas releaserom champagne and sparkling wines (ruled by Fick’s law) isherefore also expected to depend on both glass shape andngravement conditions. In a near future, we plan to accu-ately investigate the velocity field in various other modelsf champagne glasses showing natural as well as artificialffervescence. We will use the so-called PIV (particle imageelocimetry) technique to access the velocity field in cham-agne glasses. The PIV technique is a planar laser light sheetechnique in which the light sheet is pulsed twice, and imagesf fine particles lying in the light sheet are recorded on aideo camera or a photograph. The displacement of the parti-le images is measured in the plane of the image and used toetermine the displacement of the particles in the flow [8]. Welso plan to test various glass shapes (the inventive spirit oflassmakers is fertile in this field) as well as various engrave-ent conditions. Actually, the modern techniques of glass

ngravement, done to promote effervescence, enable variousodels of engravement (in terms of shape and location in

he glass), thus logically modifying the overall convection cur-ents conditions induced by artificial effervescence. Moreover,

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since we strongly suggest close links between the kinetics ofconvection currents and the kinetics of flavor release, quanti-tative measurements of the kinetics of discharge of CO2 and ofvolatile organic compounds from various champagne glassesunder various glass shape and engravement conditions arealso to be conducted, together with sensory analysis experi-ments.

Acknowledgments

Thanks are due to the Europol’Agro Institute and the Associa-tion Recherche Oenologie Champagne Universite, for financialsupport, and ARC International, for supplying us with variousglasses and for supporting our research.

e f e r e n c e s

1] G. Liger-Belair, J. Agric. Food Chem. 53 (2005) 2788.2] S. Jones, G. Evans, K. Galvin, Adv. Colloid Interf. Sci. 80 (1999)

27.3] S. Lubetkin, Langmuir 19 (2003) 2575.4] G. Liger-Belair, M. Vignes-Adler, C. Voisin, B. Robillard, P.

Jeandet, Langmuir 18 (2002) 1294.5] G. Liger-Belair, R. Marchal, P. Jeandet, Am. J. Enol. Viticult. 51

(2002) 151.6] G. Liger-Belair, J.-B. Religieux, S. Fohanno, M.-A. Vialatte, P.

Jeandet, G. Polidori, J. Agric. Food Chem. 55 (2007) 882.7] G. Liger-Belair, F. Beaumont, P. Jeandet, G. Polidori, Langmuir

23 (2007) 10976.8] M. Raffel, C. Willert, J. Kompenhans, Particle Image

Velocimetry, A Practical Guide, Springer, Berlin, 1998.

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