TrackingRedoxPotentialinWine

Dr.GordonA.Walker

Flotek/SolarisBiotechGordonWalkerConsultingLLC

Redoxvs.Reduction

RedoxPotentialofWine

•  Aromaticcompoundsarevolatileasthemolecular(reduced)formratherthantheionic(oxidized)form.

•  HigherpHfavorslowerredoxpotentialàMoreReductiveEnvironment•  LowerpHfavorshigherredoxpotentialàMoreOxidativeEnvironment

Reduction/OxidationReactions

“OILRIG”or“LEOsaysGER”

RedoxPotentialDeterminesBiologicalandChemicalDynamics

BillDudeney,ImperialCollege,UnitedKingdom

DefiningRedoxPotentialinWine

•  OxidationReductionPotential(ORP)isaquantifiablemeasurementofthetendencyofamoleculeoriontogainorloseelectrons.*

•  Redoxpotentialmediatesthefrequencyofalloxidationandreductionreactionsduringthelifeofawinethroughfermentationandaging.

*BruceZoecklein,VTemeritus

e e

HigherORPValue

LowerORPValue

OxidizingandReducingAgentsinWine

•  Oxidizingagent:ReactiveOxygenSpecies(ROS)stealelectronsfromothercompounds,causeoxidation.

•  Reducingagents(antioxidant):Ascorbicacid,SO2,phenolics,gluthathione,metalspecies(FeII,CuI)giveupelectrons,tomediateredoxpotential.

KineticsofRedoxReactionsinWine•  Fastreactions(oxidationofethanol,ascorbicacid)

•  Slowreactions(tannins/polyphenols)

•  Reactiontype/kineticsarehighlymatrixdependent

•  Equilibriumisalwaysinflux

WineFermentation

WineAging

50:50Fe(II)/Fe(III)=770mV

50:50Fe(II)Tartrate/Fe(III)Tartrate=500mV

50:50Cu(I)/Cu(II)=160mV

AdaptedfromDr.RogerBoulton

Eh=mV

Reductive“DangerZone”

pH

mV=ORP+~200

OrganicAcidComplexesDictateWineRedox

WinepH

AdaptedfromDr.RogerBoulton

RedoxMeasurementPrinciples

HamiltonCompany,SteveHammond

RedoxMeasurementPrinciples

HamiltonCompany,SteveHammond

RedoxMeasurementPrinciples

ORP=mV+OffsetValue(+220mV)HamiltonCompany,SteveHammond

YeastMetabolismisTransformative

“WineMicrobiologyforFermentationSuccessandWineQuality”VladimirJiranek

YeastMetabolism=BalancingRedox

“Redoxpotentialcontrolandapplicationsinmicroaerobicandanaerobicfermentations”Liu,etal.,BiotechnologyAdvances,2013

YeastImpactExtracellularRedox

ATPaseactivityofPma1isessentialtomaintainintracellularenvironment:enablingfermentativemetabolism,facilitatingnutrient

uptake,andmitigatingenvironmentalstressors.

ATP ADP

H+H+

ATPase:Pma1

ExtracellularEnvironmentHigher[H+]

IntracellularEnvironmentLower[H+]

pH:6.5-7

pH:2.8-4.5H+H+

H+

H+

AA

H+

ProtonStress:EtOH,OrganicAcids

AA

AASymporter

H+ H+

InternalRedox=-290mV

SaccharomycesLowerRedoxPotential

•  Yeastcreatereductiveenvironmentbydepletingoxygenandreleasingprotons.

•  Reductiveenvironmentnarrowstheecologicalniche,reducingcompetition.

•  Reductiveenvironmentcanleadtohydrogensulfideviayeastmetabolismandspontaneouschemicalformation.

O2à àH+

H2S

RedoxPotentialInFermentation

“Redoxpotentialcontrolandapplicationsinmicroaerobicandanaerobicfermentations”Liu,etal.,BiotechnologyAdvances,2013

MaximumBiomassCorrespondswithMinimumORPàH2SQuorumSensing

HistoricWorkonRedoxPotentialinWhiteWines

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Figure 1.3.1: Relationship between redox potential (Eh curve) and hydrogen sulfide (H2S curve) production during fermentation [1].

Figure 1.3.1 shows trends of different parameters during wine fermentation. The

important curves are the curves labeled H2S and Eh. The H2S curve shows the rate of hydrogen

sulfide formation and the Eh curve is the redox potential of the fermentation. The peak of the H2S

curve is at the point of lowest redox potential and as the redox potential curve increases, the rate

of H2S formation curve decreases. The natural decline in redox potential (roughly 300 mV down

to 100 mV in Rankine’s case) due to the metabolic processes in the wine fermentation seem to

create the proper reduction conditions for the elemental sulfur to reduce to H2S.

HydrogenSulfideProduction&Redox

Rankine,1963

EhcurvecorrespondstoRedoxPotential(ORP)

Hypothesis:Thelowertheredoxpotential,themoreH2Sproduced.

SpontaneousChemicalReductionofElementalSulfurintoH2S

•  Reductionpotentialforthesulfur/hydrogensulfidecoupleatwinepHis-70mV

•  Canhydrogensulfideformationfromthissourcebepreventedbythecontrolofredoxpotentialduringfermentation?

4

wines and also examined the effects of adding air [13]. This work observed that the redox

potential started at a high point, around 300 mV to 400 mV, and plunged down to a minimum

around 100 mV to 200 mV at the time when the fermentation was at its maximum rate. The

redox potential would then naturally rise after this point. Joslyn found that the rate and extent of

the rise was influenced by the aeration.

1.3 Redox Potential and Hydrogen Sulfide Production

One important redox reaction in wine involves elemental sulfur. The reaction between

elemental sulfur and H2S formation is favored at low redox potentials since it is a reduction

reaction:

! + 2!! + 2!! ⟶ !!!,!! = −450 !" !" !" = 3.5 (!"#$%&'( 1.3.1)

The extent and likelihood of this redox reaction is determined by the difference in potential

between the juice potential and the potential of the corresponding redox couple (Eh) at the juice

pH. Rankine found that the prevailing redox conditions of the wine during fermentation were

significant in determining H2S levels and rates of formation [1]. The rate of H2S formation was

greatest at the lowest redox potential levels. This suggests that it is the redox potential levels that

cause H2S to form in a natural fermentation.

“AdvancedMonitoringandControlofRedoxPotentialinWineFermentation”Killeen,AJEV,2018

TrackingRedoxPotential:OpusOneVintage2016&2017

•  OrionVersaStarpHMeter

•  OrionORPprobe

•  TankSetup:BNCWireconnections,pipes,clamps,screen,bung,probe

Cap

Must

OpusOneRedoxPotentialConclusions

•  HigherpHandtemperaturesleadtofasterfermentations,lowerORPvalues,andmoreH2Scharacter.

•  Stimulatingyeastmetabolism(O2/nutrients)drivestheORPlower,correlateswithincreaseinbiomass/cell#.

•  Clonesandotherredvarieties(datanotshown)donotappeartosignificantlyaffectORP,choiceofyeastdoes.

FutureGoalsforTrackingRedoxPotential

•  FurtherexplorehowdifferentpumpoverstrategiesaffectORPoffermentation.

•  ControlORPviapumpover/oxygenadditions.

•  Testmoreenologicalvariables(yeastspecies,nutrition,co-ferments,vineyardtreatments,smoketaint,vesseldesign,etc…)

UsingORPAsProcessParameter

•  Temperatureé(ORPê) •  Temperatureê(ORPé) •  pHé(ORPê)•  pHê(ORPé)•  DissolvedOxygené(ORPé)•  DissolvedOxygenê(ORPê)

àORPtracksindirectlywithyeastmetabolism

PredictionsforRedoxControlofWineFermentations

•  Fasterfermentations

•  Lessincidenceofstuck/sluggishferments

•  Moreyeastbiomass(goodforsurleeaging?)

•  Less“reductive”aromas

•  Controlalcoholcontent?

WhatRoleDoesRedoxPotentialPlayIn?

•  Uninoculated/NativeFerments•  MalolacticFermentation•  EnologicalTreatments(Filtering,MicroOx,etc...)•  SmokeTaint(Removal/RO)•  Spoilage(Brett/Lactics)•  EnzymaticTreatments(pectinase,lysozyme)•  LongevityinBottle

Onlywaytoknowistomeasure!

ThankYouforListening!

Questions?

GordonWalkerConsulting@gmail.comwww.GordonWalkerConsulting.comwww.FlotekCA.comwww.HamiltonCompany.com