Technical Brief In situ Measurements of Dissolved Oxygen during Low-Level Oxygenation in Red Wines

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1 Technicl Brief In situ Mesurements of Dissolved Oxygen during Low-Level Oxygention in Red Wines V. Felipe Lurie, 1 Robert Lw, 2 Willy S. Joslin, 2 nd Andrew L. Wterhouse 3 * Abstrct: Dissolved oxygen ws mesured during low-level oxygention tretments. As previously reported in the literture, continul oxygen dditions ugmented the dissolved oxygen levels of wines. Results here showed concentrtions up to 2.4 mg oxygen/l. Conversely, nonoxygented wines hd concentrtions s low s 4 µg oxygen/l in the center of the tnks. The nlysis of dissolved oxygen in winery setting requires n pproprite smpling procedure nd sensitive mesuring device. Key words: wine, oxygen, oxygention, microoxygention Microoxygention is populr commercil process in which smll mounts of oxygen re introduced in the wine mtrix with the im of improving its sensory profile (Prish et l. 2000, Rieger 2000). Although mny trde rticles hve been written on microoxygention, only few well-controlled experiments hve been published in mjor peer-reviewed scientific journls covering the effects of this prctice on wine chemistry (Atnsov et l. 2002, Lludy et l. 2006, Cno-López et l. 2006, Pérez-Mgriño et l. 2007). Clerly, more reserch is required to understnd nd better control the outcome of microoxygention. To become rective, oxygen in its nturl triplet stte, birdicl with two unpired electrons, needs to be ctivted to its singlet rdicl forms (Singleton 1987), most likely with the involvement of trnsition metls ctlysts (Dnilewicz 2003). For ctivtion to occur, oxygen must be dissolved in the wine in process in which concentrtion grdients, prtil pressure of gses, nd wine temperture re fundmentl. Compred with room temperture, oxygen solubility increses pproximtely 10% t tempertures of ~5 C. At tmospheric pressure nd room temperture, oxygen sturtion, with ir, is reched t ~6 ml/l. Under continued gittion, tht sturtion level cn be reched in pproximtely 30 sec (Ribéreu- 1 Fcultd de Ciencis Agrris, Universidd de Tlc, Tlc, Chile; 2 Wente Vineyrds, Livermore, CA 94550; nd 3 Deprtment of Viticulture nd Enology, University of Cliforni, Dvis, CA *Corresponding uthor (fx: ; emil: lwterhouse@ucdvis. edu) Acknowledgments: The uthors thnk the Americn Vineyrd Foundtion, Cliforni Competitive Grnt, nd Wente Vineyrds. V.F.L. lso thnks the Fulbright, Lspu, Wine Specttor, Rhone Rngers, nd Jstro Shields Scholrships, nd the ssistnce of Annegret Rust. Oenodev microoxygention system ws provided by Vinovtion, Sebstopol, CA. Mnuscript submitted June 2006; revised September 2006, November 2007 Copyright 2008 by the Americn Society for Enology nd Viticulture. All rights reserved. 215 Gyon 1933). After oxygen depletion, severl new uptkes cn occur, resulting in totl consumption of ~60 to over 600 mg/l O 2 for white nd red wines, respectively (Singleton 1987). If wine were insted exposed to high doses of pure oxygen, then sturtion levels of ~30 ml/l would be expected (Singleton 2000). Nonetheless, with the typicl oxygen flow rtes used in microoxygention, the dissolved oxygen (DO) concentrtion of wine is not expected to pproch such levels (Wterhouse nd Lurie 2006). Dissolved oxygen redings between ~10 nd 120 µg/l hve been reported for wines undergoing microoxygention (Cstellri et l. 2004). The sensors most typiclly used for DO determintions re electrolytic cell bsed methods (Rmmoorthy et l. 2003, Cheynier et l. 2002). These sensors give ccess to prtil pressures nd cn be clibrted in percentge sturtion (Moutounet nd Mzuric 2001, Cheynier et l. 2002). In these systems, the sensor consists of severl electrodes submerged in n electrolyte solution nd seprted from the exterior by n oxygen-permeble membrne. When n electricl potentil is pplied between the two electrodes, the oxygen is reduced, thus generting n electricl response tht is proportionl to the oxygen content (Rmmoorthy et l. 2003). The purpose of this reserch ws to describe the levels of dissolved oxygen in industril wine tnks during microoxygention tretments. This leds to recommendtions for dissolved oxygen mesurement techniques nd discussion of the effectiveness of such mesurements in typicl winery setting. Mterils nd Methods Wines. Two different experiments, conducted over two consecutive vintges, (experiment I) nd (experiment II), were performed t Wente Winery, Livermore, Cliforni. In experiment I, Cbernet Suvignon grpes from Livermore (23.5 Brix), were destemmed, crushed, fermented, pressed, nd trnsferred

2 216 Lurie et l. into single 132,489-L tnk where mlolctic fermenttion (MLF) took plce. No sulfur dioxide ws dded t this stge. After MLF completion, the wine ws settled for four dys, nd the clen superntnt (no turbidity mesurements were performed) rcked to four tnks of 11,553 L ech to proceed with oxygention tretments. At this point wine composition ws ethnol concentrtion, 14.1%; ph, 3.9; titrtble cidity, 6.6 g trtric cid/l; totl polyphenolics, 2393 mg gllic cid equivlents/l; residul sugrs, 1.6 g/l; free SO 2, 8 mg/l; nd totl SO 2, 12 mg/l. In experiment II, to reduce the possibility of unwnted microbil growth, similr type of wine ws vinified s in experiment I nd ws treted using high-temperture short-time (~70 C for 15 sec followed by cooling to 15 C). Wine composition ws ethnol concentrtion, 14.8%; ph, 3.75; titrtble cidity, 5.7 g trtric cid/l; totl polyphenolics, 2734 mg gllic cid equivlents/l; residul sugrs, 1.9 g/l; free SO 2, 10 mg/l; nd totl SO 2, 12 mg/l. In both experiments, the wines were rcked using nitrogen blnketing in the source tnk nd dry ice in the reception tnks to mintin the concentrtions of DO s low s possible. Concentrtions of DO in ll tnks before the strt of oxygention tretments were between 15 nd 25 µg/l. Oxygen delivery system. Oxygen gs, 99% purity (Airgs, Woodlnd, CA) ws delivered into the wine tnks using Nylotube tubing (6.35 mm dim) (NewAge Industries, Southmpton, PA) from 7778-L (275 cubic feet) oxygen cylinder (Figure 1). During experiment I, the oxygen flow pplied ws regulted with custom-built flow controller nd checked periodiclly with clibrted stndrd gs bubble meter. The oxygen bubbles were creted using 1-micron porous stinless-steel cylindric sprger (6.35 mm dim x 12.7 mm length) locted ~30 cm from the bottom of the tnk. During experiment II, oxygen flow ws regulted by commercil microoxygention systems (Stvin, Suslito, CA; Oenodev, Villeneuve-lés- Mguelones, Frnce), while oxygen bubbles were generted using 1-micron porous stinless-steel cylinder (6.35 x 12.7 mm) in two of the tnks nd commercil oxygen diffuser (Oenodev) in the third tnk. The control tnk ws not oxygented. Oxygention regimes. For experiment I, Cbernet Suvignon, with nd without ok stves bundled to tnk inner wlls, ws subject to four tretments: (1) no oxygen no ok: no oxygen ddition nd no ok stves presence; (2) oxygen no ok: oxygen ddition t fixed rte of 5 ml oxygen/l of wine per month for 6 months nd no ok stves; (3) no oxygen ok: no oxygen ddition, nd ok stves (80.3 cm 2 French ok stves, medium plus tost [Stvin] per L of wine, bundled to the tnk inside wlls with stinless-steel wire); nd (4) oxygen ok: oxygen ddition (s in tretment 2) nd ok stves (s in tretment 3). For experiment II, no ok stves were included, nd ech wine tretment (lbeled oxygen 1, 2, 3, nd no oxygen) ws treted with different oxygen rtes (see Tble 1). These doses were suggested by provider of the microoxygention technique in Cliforni, fter periodic winetsting. In this cse, oxygention tretment strted before MLF, cesed during this process, nd continued fter MLF completion, which ws induced by direct inocultion of lctic cid bcteri. Dissolved oxygen in tnks. To llow for wine smpling nd DO determintions while keeping the tnks closed t ll times, smple circultion circuit constructed in 316 stinless-steel tubing (6.35 mm dim) (Webco Industries, Knss City, MO) with gs purge on top of the tnks ws used (Figure 1). The oxygen no ok tretment ws set up with four smpling points t different loctions in the tnk: (1) top front bove the sprger, (2) top rer, (3) bottom rer, nd (4) center. All other tnks were smpled from the center. Dissolved oxygen concentrtions were mesured in situ using n Orbisphere 2713 series oxygen nlyzer, model indicting instrument, nd model 2110 sen- Figure 1 Schemtic digrm of experimentl setup: wine tnk, oxygen delivery, nd dissolved oxygen mesurement system. Tble 1 Oxygention regime, pre- nd postmlolctic fermenttion (MLF), during experiment II. Oxygention rtes ml/l/month Dys Oxy 1 Oxy 2 Oxy 3 No oxy Pre-MLF Post-MLF

3 In situ Mesurements of Dissolved Oxygen 217 Tble 2 Reproducibility of dissolved oxygen mesurements for four wines sturted with different clibrted gs smples from 0 to 4% oxygen. Dissolved oxygen (mg/l) O 2 -gs (%) R 2 R 3 Men SD % SD x R 3, replictions performed t different dtes; SD, stndrd devition. All mesurements were tken t room temperture nd tmospheric pressure. sor (Orbisphere, Genev, Switzerlnd). The nlyzing principle of the sensor is bsed on tht of n electrolytic cell. Mesurements were red on weekly or monthly bsis, depending on the stge of the tretment. Before every reding, the DO meter ws clibrted using irsturted wter s stndrd ccording to mnufcturer instructions. The sensors were periodiclly purged with nitrogen to check the zero clibrtion. The sensors were reconditioned nd the membrnes replced if the zero clibrtion ws bove 2 µg/l. To test the reproducibility of the mesurements t different DO concentrtions (µg to mg/l), four clibrted gs smples from 0 to 4% oxygen (Air Liquide, Houston, TX) were sprged into 5-L continer with Cbernet Suvignon wine until sturtion ws reched. Ech tretment ws smpled t three different dtes, using circultion circuit s previously described, obtining percent stndrd devition vlues <3% (Tble 2). Repetbility mesures were performed t three different dtes during experiment I, giving vlues below 4% (Tble 3). Other nlyses. Wine temperture ws mesured using the Orbisphere equipment, nd microbil popultions were monitored using counting chmbers, Petroff Husser for bcteri nd Levy Husser for yest ccording to mnufcturer protocols (Husser Scientific, Horshm, PA). While temperture hs mrked effect on oxygen dissolution (Singleton 2000), microbes might consume prt of the oxygen dded nd eventully spoil the wine being treted (Drysdle nd Fleet 1988, Forniron-Bonnefond et l. 2003). Wine composition nlyses (ethnol content by ebuillometry, ph, titrtble cidity, totl polyphenolics by Folin-Cioclteu, nd free nd totl sulfur dioxide by ertion-oxidtion) were crried out ccording to stndrd procedures (Ough nd Amerine 1988). Results nd Discussion Dissolved oxygen in tnks. Experiment I. After the first month of oxygention, the oxygented tretments, with or without ok stves, hd incresing DO concentrtions rnging from ~50 to 270 µg/l, while the tretments without oxygen ddition showed lower nd firly consistent concentrtions t ~25 to 30 µg/l. These concentrtions re close to the medin reported (24 mg/l) for 175 red wines in stinless-steel tnks (Cstellri et l. 2004) nd those reported elsewhere (Cheynier t l. 2002). After 6 month of oxygention, the oxygen-treted wines hd ~10-fold more DO thn the untreted tnks (Figure 2). In ddition, the presence of ok stves did not seem to hve significnt effect on DO, either t the beginning of the experiment or lter. A similr effect ws reported when oxygen ws dded t doses of 5 ml O 2 /L wine per month (Cstellri et l. 2004). Regulr monitoring of wine temperture throughout the experiment showed minor diurnl vrition (<2 C), nd virtully no temperture disprity between tnks (<0.3 C), with sesonl devition from 13.5 to 17.5 C. The fluctution in DO observed for the oxygented tretment between My nd July ws consistent with n increse of 2 to 2.5 C in temperture observed in My, while no unusul microbil growth ws detected t this or ny stge throughout the experiment (dt not presented). Although such temperture rises might result in reduction of the oxygen solubility, we were unble to explin the observed DO drop. Oxygen concentrtion mesurements in the vented gs from these tnks suggested tht more thn 80% of the oxygen dded ws being consumed. The oxygen injection rtes were ~1 ml/min, with vent gs rtes vrying between 3 nd 8 ml/min over the 6 months of experimentl period. Additionl mesurements to evlute the DO t the four smpling points in the oxygen no ok tretment (Figure 1) showed very little vrition (<4%), indicting n even DO distribution in this tnk over 6 months of tretment. Tble 3 Repetbility of dissolved oxygen mesurements, performed t three different dtes during experiment I: oxygen no ok tretment. Dissolved oxygen (mg/l) R 2 R 3 R 4 Men SD % SD Feb Feb Feb R 4, replictions 1 to 4; SD, stndrd devition. Figure 2 Dissolved oxygen mesurements, experiment I.

4 218 Lurie et l. Typicl wine composition vlues were observed t the end of experiment I (Tble 4). The vrition in phenolic concentrtion could be explined by the extrction of phenolic species from the ok stves. Experiment II. Similr to experiment I, the DO concentrtion in the oxygented tnks showed consistently higher vlues thn the control, especilly before MLF (Figure 3A), when higher oxygen flow rtes were pplied (Tble 1). Dissolved oxygen in the control tnk ws between ~4 nd 14 µg/l, while DO in oxygented tnks ws between ~220 nd 2400 µg/l. After mlolctic fermenttion, when the oxygen doses were reduced to between 4 nd 0.5 ml oxygen/l wine per month, the differences between the oxygen-treted tnks nd the control become less noticeble (Figure 3B). DO vlues for the control were between 7 nd 23 μg/l, while vlues for the oxygen-treted tnks were between ~8 nd 60 μg/l. Once gin, temperture mesurements were consistent cross tnks, nd diurnl vritions were less thn 2.5 C. The sesonl devition in wine temperture registered ws between 13.0 nd 18.5 C. Wine composition dt t the end of experiment II re presented in Tble 4. Considering the limittions to the experimentl design of these industril-scle experiments, these dt cn only be used s n indiction of the possible effects of oxygen exposure on wine chemistry. The pprent lower levels of totl phenolics observed in the oxygen-treted wines could hve been the result of precipittion due to higher phenolic polymeriztion. The bove confirms previous observtions indicting tht discrimintion between oxygen levels when using low rtes of oxygen tretment demnds the use of very sensitive equipment nd pproprite smpling procedures tht exclude oxygen before nd during mesurements. It is prmount tht winemkers py specil ttention to prctices in which low tempertures re used, s higher dissolved oxygen rtes will be expected (Cstellri et l. 2004, Wterhouse nd Lurie 2006). Tble 4 Bsic enologicl prmeters fter oxygen tretment. Experiment I EtOH (% v/v) ph TA (g/l) TP (mg/l) SO 2 (F/T) (mg/l) No oxygen no ok /61 Oxygen no ok /64 No oxygen ok /61 Oxygen ok /64 Experiment II Oxygen /68 Oxygen /73 Oxygen /71 No oxygen /70 EtOH, ethnol; TA, titrtble cidity s trtric cid; TP, totl phenolics s gllic cid; F/T, free nd totl sulfur dioxide. Figure 3 Dissolved oxygen mesurements, experiment I: premlolctic (A) nd postmlolctic (B) fermenttion. Conclusions Dissolved oxygen incresed with low-level oxygention tretments, suggesting tht the rte of oxygen consumption is slower thn tht of oxygen dissolution. The low levels of oxygen demnd specilized oxygen meters for ccurte nd precise mesurements. In this cse, these increses were noticeble with doses s low s 1 ml/l of wine per month, regrdless of which oxygen delivery system ws used. Literture Cited Atnsov, V., H. Fulcrnd, V. Cheynier, nd M. Moutonet Effect of oxygention on polyphenol chnges occurring in the course of wine-mking. Anl. Chim. Act 458: Cno-López, M., F. Prdo-Minguez, J.M. López-Roc, nd E. Gómez-Plz Effect of microoxygention on nthocynin nd derived pigment content nd chromtic chrcteristics of red wines. Am. J. Enol. Vitic. 57: Cstellri, M., B. Simonto, G.B. Tornielli, P. Spinelli, nd R. Ferrrini Effects of different enologicl tretments on dissolved oxygen in wines. Itl. J. Food Sci. 16: Cheynier, V., V. Atnsov, H. Fulcrnd, J.P. Mzuric, nd M. Moutonet Oxygen in wine nd its role in phenolic rections during geing. In Use of Gses in Winemking. M. Allen et l. (Eds.), pp ASVO Seminr Proceedings. Winetitles, Ashford, Austrli. Dnilewicz, J.C Review of rection mechnisms of oxygen nd proposed intermedite reduction products in wine: Centrl role of iron nd copper. Am. J. Enol. Vitic. 54:73-85.

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