diff --git a/applications/solvers/combustion/fireFoam/YEEqn.H b/applications/solvers/combustion/fireFoam/YEEqn.H
index 6726a1964f..f16d6e523a 100644
--- a/applications/solvers/combustion/fireFoam/YEEqn.H
+++ b/applications/solvers/combustion/fireFoam/YEEqn.H
@@ -11,11 +11,10 @@ tmp<fv::convectionScheme<scalar>> mvConvection
 {
     radiation->correct();
     combustion->correct();
-    volScalarField Yt(0.0*Y[0]);
 
     forAll(Y, i)
     {
-        if (i != inertIndex && composition.active(i))
+        if (composition.solve(i))
         {
             volScalarField& Yi = Y[i];
 
@@ -38,14 +37,10 @@ tmp<fv::convectionScheme<scalar>> mvConvection
             YiEqn.solve("Yi");
 
             fvOptions.correct(Yi);
-
-            Yi.max(0.0);
-            Yt += Yi;
         }
     }
 
-    Y[inertIndex] = scalar(1) - Yt;
-    Y[inertIndex].max(0.0);
+    composition.normalise();
 
     volScalarField& he = thermo.he();
 
diff --git a/applications/solvers/combustion/fireFoam/createFieldRefs.H b/applications/solvers/combustion/fireFoam/createFieldRefs.H
index a911c586d9..af15effbc2 100644
--- a/applications/solvers/combustion/fireFoam/createFieldRefs.H
+++ b/applications/solvers/combustion/fireFoam/createFieldRefs.H
@@ -1,4 +1,3 @@
 const volScalarField& psi = thermo.psi();
 const volScalarField& T = thermo.T();
 regionModels::surfaceFilmModel& surfaceFilm = tsurfaceFilm();
-const label inertIndex(composition.species()[inertSpecie]);
diff --git a/applications/solvers/combustion/fireFoam/createFields.H b/applications/solvers/combustion/fireFoam/createFields.H
index 12c5a7ef66..a2bf22df2f 100644
--- a/applications/solvers/combustion/fireFoam/createFields.H
+++ b/applications/solvers/combustion/fireFoam/createFields.H
@@ -8,15 +8,6 @@ SLGThermo slgThermo(mesh, thermo);
 basicSpecieMixture& composition = thermo.composition();
 PtrList<volScalarField>& Y = composition.Y();
 
-const word inertSpecie(thermo.properties().lookup("inertSpecie"));
-if (!composition.species().found(inertSpecie))
-{
-    FatalIOErrorIn(args.executable().c_str(), thermo.properties())
-        << "Inert specie " << inertSpecie << " not found in available species "
-        << composition.species()
-        << exit(FatalIOError);
-}
-
 Info<< "Creating field rho\n" << endl;
 volScalarField rho
 (
diff --git a/applications/solvers/combustion/reactingFoam/YEqn.H b/applications/solvers/combustion/reactingFoam/YEqn.H
index 8149acd6a0..d8f9453940 100644
--- a/applications/solvers/combustion/reactingFoam/YEqn.H
+++ b/applications/solvers/combustion/reactingFoam/YEqn.H
@@ -11,11 +11,10 @@ tmp<fv::convectionScheme<scalar>> mvConvection
 
 {
     reaction->correct();
-    volScalarField Yt(0.0*Y[0]);
 
     forAll(Y, i)
     {
-        if (i != inertIndex && composition.active(i))
+        if (composition.solve(i))
         {
             volScalarField& Yi = Y[i];
 
@@ -36,12 +35,8 @@ tmp<fv::convectionScheme<scalar>> mvConvection
             YiEqn.solve("Yi");
 
             fvOptions.correct(Yi);
-
-            Yi.max(0.0);
-            Yt += Yi;
         }
     }
 
-    Y[inertIndex] = scalar(1) - Yt;
-    Y[inertIndex].max(0.0);
+    composition.normalise();
 }
diff --git a/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFieldRefs.H b/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFieldRefs.H
index fdc479bc23..6e1184a1fa 100644
--- a/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFieldRefs.H
+++ b/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFieldRefs.H
@@ -1,3 +1,2 @@
 const volScalarField& psi = thermo.psi();
 const volScalarField& T = thermo.T();
-const label inertIndex(composition.species()[inertSpecie]);
diff --git a/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFields.H b/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFields.H
index a2457c3ea2..1588e48139 100644
--- a/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFields.H
+++ b/applications/solvers/combustion/reactingFoam/buoyantReactingFoam/createFields.H
@@ -8,15 +8,6 @@ thermo.validate(args.executable(), "h", "e");
 basicSpecieMixture& composition = thermo.composition();
 PtrList<volScalarField>& Y = composition.Y();
 
-const word inertSpecie(thermo.properties().lookup("inertSpecie"));
-if (!composition.species().found(inertSpecie))
-{
-    FatalIOErrorIn(args.executable().c_str(), thermo.properties())
-        << "Inert specie " << inertSpecie << " not found in available species "
-        << composition.species()
-        << exit(FatalIOError);
-}
-
 volScalarField rho
 (
     IOobject
diff --git a/applications/solvers/combustion/reactingFoam/createFieldRefs.H b/applications/solvers/combustion/reactingFoam/createFieldRefs.H
index fdc479bc23..6e1184a1fa 100644
--- a/applications/solvers/combustion/reactingFoam/createFieldRefs.H
+++ b/applications/solvers/combustion/reactingFoam/createFieldRefs.H
@@ -1,3 +1,2 @@
 const volScalarField& psi = thermo.psi();
 const volScalarField& T = thermo.T();
-const label inertIndex(composition.species()[inertSpecie]);
diff --git a/applications/solvers/combustion/reactingFoam/createFields.H b/applications/solvers/combustion/reactingFoam/createFields.H
index 28b7b8199a..16e38c2ef2 100644
--- a/applications/solvers/combustion/reactingFoam/createFields.H
+++ b/applications/solvers/combustion/reactingFoam/createFields.H
@@ -8,15 +8,6 @@ thermo.validate(args.executable(), "h", "e");
 basicSpecieMixture& composition = thermo.composition();
 PtrList<volScalarField>& Y = composition.Y();
 
-const word inertSpecie(thermo.properties().lookup("inertSpecie"));
-if (!composition.species().found(inertSpecie))
-{
-    FatalIOErrorIn(args.executable().c_str(), thermo.properties())
-        << "Inert specie " << inertSpecie << " not found in available species "
-        << composition.species()
-        << exit(FatalIOError);
-}
-
 volScalarField rho
 (
     IOobject
diff --git a/applications/solvers/combustion/reactingFoam/setRDeltaT.H b/applications/solvers/combustion/reactingFoam/setRDeltaT.H
index b64616057e..73423173c7 100644
--- a/applications/solvers/combustion/reactingFoam/setRDeltaT.H
+++ b/applications/solvers/combustion/reactingFoam/setRDeltaT.H
@@ -111,7 +111,7 @@ License
 
         forAll(Y, i)
         {
-            if (i != inertIndex && composition.active(i))
+            if (composition.solve(i))
             {
                 volScalarField& Yi = Y[i];
 
diff --git a/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/YEqn.H b/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/YEqn.H
index 612711f4c6..6fd2c3041a 100644
--- a/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/YEqn.H
+++ b/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/YEqn.H
@@ -1,24 +1,9 @@
 {
     reaction.correct();
 
-    tmp<volScalarField> Yt(nullptr);
-
-    if (Y.size())
-    {
-        Yt = tmp<volScalarField>
-        (
-            new volScalarField
-            (
-                IOobject("Yt", runTime.timeName(), mesh),
-                mesh,
-                dimensionedScalar(dimless, 0)
-            )
-        );
-    }
-
     forAll(Y, i)
     {
-        if (i != inertIndex && composition.active(i))
+        if (composition.solve(i))
         {
             volScalarField& Yi = Y[i];
 
@@ -38,15 +23,8 @@
             YiEqn.solve("Yi");
 
             fvOptions.correct(Yi);
-
-            Yi.max(0.0);
-            Yt.ref() += Yi;
         }
     }
 
-    if (Y.size())
-    {
-        Y[inertIndex] = scalar(1) - Yt;
-        Y[inertIndex].max(0.0);
-    }
+    composition.normalise();
 }
diff --git a/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/setRegionFluidFields.H b/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/setRegionFluidFields.H
index a9b10b4c8b..0f7e377b6b 100644
--- a/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/setRegionFluidFields.H
+++ b/applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/setRegionFluidFields.H
@@ -8,21 +8,6 @@
     basicSpecieMixture& composition = thermo.composition();
     PtrList<volScalarField>& Y = composition.Y();
 
-    label inertIndex = -1;
-    if (Y.size())
-    {
-        const word inertSpecie(thermo.properties().lookup("inertSpecie"));
-        if (!composition.species().found(inertSpecie))
-        {
-            FatalIOErrorIn(args.executable().c_str(), thermo.properties())
-                << "Inert specie " << inertSpecie
-                << " not found in available species "
-                << composition.species()
-                << exit(FatalIOError);
-        }
-        inertIndex = composition.species()[inertSpecie];
-    }
-
     volScalarField& rho = rhoFluid[i];
     volVectorField& U = UFluid[i];
     surfaceScalarField& phi = phiFluid[i];
diff --git a/applications/solvers/lagrangian/reactingParticleFoam/YEqn.H b/applications/solvers/lagrangian/reactingParticleFoam/YEqn.H
index 6edb9c2b27..e958c91bdd 100644
--- a/applications/solvers/lagrangian/reactingParticleFoam/YEqn.H
+++ b/applications/solvers/lagrangian/reactingParticleFoam/YEqn.H
@@ -17,24 +17,9 @@ if (Y.size())
 {
     combustion->correct();
 
-    tmp<volScalarField> Yt(nullptr);
-
-    if (Y.size())
-    {
-        Yt = tmp<volScalarField>
-        (
-            new volScalarField
-            (
-                IOobject("Yt", runTime.timeName(), mesh),
-                mesh,
-                dimensionedScalar(dimless, 0)
-            )
-        );
-    }
-
     forAll(Y, i)
     {
-        if (i != inertIndex && composition.active(i))
+        if (composition.solve(i))
         {
             volScalarField& Yi = Y[i];
 
@@ -57,15 +42,8 @@ if (Y.size())
             YEqn.solve("Yi");
 
             fvOptions.correct(Yi);
-
-            Yi.max(0.0);
-            Yt.ref() += Yi;
         }
     }
 
-    if (Y.size())
-    {
-        Y[inertIndex] = scalar(1) - Yt;
-        Y[inertIndex].max(0.0);
-    }
+    composition.normalise();
 }
diff --git a/applications/solvers/lagrangian/reactingParticleFoam/createFieldRefs.H b/applications/solvers/lagrangian/reactingParticleFoam/createFieldRefs.H
index ab53cceb6f..1e7b8954eb 100644
--- a/applications/solvers/lagrangian/reactingParticleFoam/createFieldRefs.H
+++ b/applications/solvers/lagrangian/reactingParticleFoam/createFieldRefs.H
@@ -1,18 +1,3 @@
-label inertIndex = -1;
-if (Y.size())
-{
-    const word inertSpecie(thermo.properties().lookup("inertSpecie"));
-    if (!composition.species().found(inertSpecie))
-    {
-        FatalIOErrorIn(args.executable().c_str(), thermo.properties())
-            << "Inert specie " << inertSpecie
-            << " not found in available species "
-            << composition.species()
-            << exit(FatalIOError);
-    }
-    inertIndex = composition.species()[inertSpecie];
-}
-
 const volScalarField& T = thermo.T();
 const volScalarField& psi = thermo.psi();
 regionModels::surfaceFilmModel& surfaceFilm = tsurfaceFilm();
diff --git a/applications/solvers/lagrangian/simpleReactingParticleFoam/YEqn.H b/applications/solvers/lagrangian/simpleReactingParticleFoam/YEqn.H
index df6fb70471..5ab0d5944d 100644
--- a/applications/solvers/lagrangian/simpleReactingParticleFoam/YEqn.H
+++ b/applications/solvers/lagrangian/simpleReactingParticleFoam/YEqn.H
@@ -11,11 +11,10 @@ tmp<fv::convectionScheme<scalar>> mvConvection
 
 {
     combustion->correct();
-    volScalarField Yt(0.0*Y[0]);
 
     forAll(Y, i)
     {
-        if (i != inertIndex && composition.active(i))
+        if (composition.solve(i))
         {
             volScalarField& Yi = Y[i];
 
@@ -36,12 +35,8 @@ tmp<fv::convectionScheme<scalar>> mvConvection
             YEqn.solve("Yi");
 
             fvOptions.correct(Yi);
-
-            Yi.max(0.0);
-            Yt += Yi;
         }
     }
 
-    Y[inertIndex] = scalar(1) - Yt;
-    Y[inertIndex].max(0.0);
+    composition.normalise();
 }
diff --git a/applications/solvers/lagrangian/simpleReactingParticleFoam/createFieldRefs.H b/applications/solvers/lagrangian/simpleReactingParticleFoam/createFieldRefs.H
index fdc479bc23..6e1184a1fa 100644
--- a/applications/solvers/lagrangian/simpleReactingParticleFoam/createFieldRefs.H
+++ b/applications/solvers/lagrangian/simpleReactingParticleFoam/createFieldRefs.H
@@ -1,3 +1,2 @@
 const volScalarField& psi = thermo.psi();
 const volScalarField& T = thermo.T();
-const label inertIndex(composition.species()[inertSpecie]);
diff --git a/applications/solvers/lagrangian/simpleReactingParticleFoam/createFields.H b/applications/solvers/lagrangian/simpleReactingParticleFoam/createFields.H
index 001e5d83e9..077a355cf1 100644
--- a/applications/solvers/lagrangian/simpleReactingParticleFoam/createFields.H
+++ b/applications/solvers/lagrangian/simpleReactingParticleFoam/createFields.H
@@ -10,15 +10,6 @@ SLGThermo slgThermo(mesh, thermo);
 basicSpecieMixture& composition = thermo.composition();
 PtrList<volScalarField>& Y = composition.Y();
 
-const word inertSpecie(thermo.properties().lookup("inertSpecie"));
-if (!composition.species().found(inertSpecie))
-{
-    FatalIOErrorIn(args.executable().c_str(), thermo.properties())
-        << "Inert specie " << inertSpecie << " not found in available species "
-        << composition.species()
-        << exit(FatalIOError);
-}
-
 volScalarField& p = thermo.p();
 
 volScalarField rho
diff --git a/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.C b/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.C
index 3080d4a895..9303bf666a 100644
--- a/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.C
+++ b/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.C
@@ -52,24 +52,13 @@ Foam::MultiComponentPhaseModel<BasePhaseModel>::MultiComponentPhaseModel
         "residualAlpha",
         dimless,
         fluid.mesh().solverDict("Yi")
-    ),
-    inertIndex_(-1)
+    )
 {
-    const word inertSpecie
-    (
-        this->thermo_->properties().lookupOrDefault("inertSpecie", word::null)
-    );
-
-    if (inertSpecie != word::null)
-    {
-        inertIndex_ = this->thermo_->composition().species()[inertSpecie];
-    }
-
     PtrList<volScalarField>& Y = this->thermo_->composition().Y();
 
     forAll(Y, i)
     {
-        if (i != inertIndex_ && this->thermo_->composition().active(i))
+        if (this->thermo_->composition().solve(i))
         {
             const label j = YActive_.size();
             YActive_.resize(j + 1);
@@ -91,42 +80,7 @@ Foam::MultiComponentPhaseModel<BasePhaseModel>::~MultiComponentPhaseModel()
 template<class BasePhaseModel>
 void Foam::MultiComponentPhaseModel<BasePhaseModel>::correctSpecies()
 {
-    volScalarField Yt
-    (
-        IOobject
-        (
-            IOobject::groupName("Yt", this->name()),
-            this->fluid().mesh().time().timeName(),
-            this->fluid().mesh()
-        ),
-        this->fluid().mesh(),
-        dimensionedScalar(dimless, 0)
-    );
-
-    PtrList<volScalarField>& Yi = YRef();
-
-    forAll(Yi, i)
-    {
-        if (i != inertIndex_)
-        {
-            Yi[i].max(0);
-            Yt += Yi[i];
-        }
-    }
-
-    if (inertIndex_ != -1)
-    {
-        Yi[inertIndex_] = scalar(1) - Yt;
-        Yi[inertIndex_].max(0);
-    }
-    else
-    {
-        forAll(Yi, i)
-        {
-            Yi[i] /= Yt;
-        }
-    }
-
+    this->thermo_->composition().normalise();
     BasePhaseModel::correctSpecies();
 }
 
diff --git a/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.H b/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.H
index 0764d83ed5..ff2f85e72f 100644
--- a/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.H
+++ b/applications/solvers/multiphase/multiphaseEulerFoam/phaseSystems/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.H
@@ -59,9 +59,6 @@ protected:
         //- Residual phase fraction
         dimensionedScalar residualAlpha_;
 
-        //- Inert species index
-        label inertIndex_;
-
         //- Pointer list to active species
         UPtrList<volScalarField> YActive_;
 
diff --git a/src/combustionModels/singleStepCombustion/singleStepCombustion.C b/src/combustionModels/singleStepCombustion/singleStepCombustion.C
index e78c370f2e..b10ffc0239 100644
--- a/src/combustionModels/singleStepCombustion/singleStepCombustion.C
+++ b/src/combustionModels/singleStepCombustion/singleStepCombustion.C
@@ -69,8 +69,8 @@ void singleStepCombustion<ThermoType>:: massAndAirStoichRatios()
     const scalar Wu = mixture_.specieThermos()[fuelIndex_].W();
 
     stoicRatio_ =
-       (mixture_.specieThermos()[inertIndex_].W()
-      * specieStoichCoeffs_[inertIndex_]
+        (mixture_.specieThermos()[mixture_.defaultSpecie()].W()
+      * specieStoichCoeffs_[mixture_.defaultSpecie()]
       + mixture_.specieThermos()[O2Index].W()
       * mag(specieStoichCoeffs_[O2Index]))
       / (Wu*mag(specieStoichCoeffs_[fuelIndex_]));
@@ -166,7 +166,6 @@ singleStepCombustion<ThermoType>::singleStepCombustion
     specieStoichCoeffs_(mixture_.species().size(), 0.0),
     Yprod0_(mixture_.species().size(), 0.0),
     fres_(Yprod0_.size()),
-    inertIndex_(mixture_.species()[thermo.properties().lookup("inertSpecie")]),
     fuelIndex_(mixture_.species()[thermo.properties().lookup("fuel")]),
     specieProd_(Yprod0_.size(), 1),
     wFuel_
@@ -312,7 +311,7 @@ void singleStepCombustion<ThermoType>::fresCorrect()
     forAll(reaction.rhs(), i)
     {
         const label speciei = reaction.rhs()[i].index;
-        if (speciei != inertIndex_)
+        if (speciei != mixture_.defaultSpecie())
         {
             forAll(fres_[speciei], celli)
             {
diff --git a/src/combustionModels/singleStepCombustion/singleStepCombustion.H b/src/combustionModels/singleStepCombustion/singleStepCombustion.H
index 4ef49eada4..e735d8a6d9 100644
--- a/src/combustionModels/singleStepCombustion/singleStepCombustion.H
+++ b/src/combustionModels/singleStepCombustion/singleStepCombustion.H
@@ -83,9 +83,6 @@ protected:
         //- List of components residual
         PtrList<volScalarField> fres_;
 
-        //- Inert specie index
-        label inertIndex_;
-
         //- Fuel specie index
         label fuelIndex_;
 
@@ -157,9 +154,6 @@ public:
             //- Return the list of components residual
             inline tmp<volScalarField> fres(const label index) const;
 
-            //- Return the inert specie index
-            inline label inertIndex() const;
-
             //- Return the fuel specie index
             inline label fuelIndex() const;
 
diff --git a/src/combustionModels/singleStepCombustion/singleStepCombustionI.H b/src/combustionModels/singleStepCombustion/singleStepCombustionI.H
index 530b2d3219..49870872ee 100644
--- a/src/combustionModels/singleStepCombustion/singleStepCombustionI.H
+++ b/src/combustionModels/singleStepCombustion/singleStepCombustionI.H
@@ -90,13 +90,6 @@ inline tmp<volScalarField> singleStepCombustion<ThermoType>::fres
 }
 
 
-template<class ThermoType>
-inline label singleStepCombustion<ThermoType>::inertIndex() const
-{
-    return inertIndex_;
-}
-
-
 template<class ThermoType>
 inline label singleStepCombustion<ThermoType>::fuelIndex() const
 {
diff --git a/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.C b/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.C
index e5dca750b9..e44ee878a2 100644
--- a/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.C
+++ b/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.C
@@ -44,10 +44,37 @@ Foam::basicSpecieMixture::basicSpecieMixture
 )
 :
     basicMixture(thermoDict, mesh, phaseName),
+    phaseName_(phaseName),
     species_(specieNames),
+    defaultSpecie_
+    (
+        species_.size()
+      ? (
+          thermoDict.found("inertSpecie")
+        ? thermoDict.lookup("inertSpecie")
+        : thermoDict.lookup("defaultSpecie")
+        )
+      : word("undefined")
+    ),
+    defaultSpecieIndex_(-1),
     active_(species_.size(), true),
     Y_(species_.size())
 {
+    if (species_.size())
+    {
+        if (species_.found(defaultSpecie_))
+        {
+            defaultSpecieIndex_ = species_[defaultSpecie_];
+        }
+        else
+        {
+            FatalIOErrorInFunction(thermoDict)
+                << "default specie " << defaultSpecie_
+                << " not found in available species " << species_
+                << exit(FatalIOError);
+        }
+    }
+
     tmp<volScalarField> tYdefault;
 
     forAll(species_, i)
@@ -85,7 +112,10 @@ Foam::basicSpecieMixture::basicSpecieMixture
             // Read Ydefault if not already read
             if (!tYdefault.valid())
             {
-                word YdefaultName(IOobject::groupName("Ydefault", phaseName));
+                const word YdefaultName
+                (
+                    IOobject::groupName("Ydefault", phaseName)
+                );
 
                 IOobject timeIO
                 (
@@ -147,8 +177,72 @@ Foam::basicSpecieMixture::basicSpecieMixture
         }
     }
 
-    // Do not enforce constraint of sum of mass fractions to equal 1 here
-    // - not applicable to all models
+    correctMassFractions();
+}
+
+
+void Foam::basicSpecieMixture::correctMassFractions()
+{
+    if (species_.size())
+    {
+        tmp<volScalarField> tYt
+        (
+            volScalarField::New
+            (
+                IOobject::groupName("Yt", phaseName_),
+                Y_[0],
+                calculatedFvPatchScalarField::typeName
+            )
+        );
+        volScalarField& Yt = tYt.ref();
+
+        for (label i=1; i<Y_.size(); i++)
+        {
+            Yt += Y_[i];
+        }
+
+        if (mag(max(Yt).value()) < rootVSmall)
+        {
+            FatalErrorInFunction
+                << "Sum of mass fractions is zero for species " << species()
+                << exit(FatalError);
+        }
+
+        forAll(Y_, i)
+        {
+            Y_[i] /= Yt;
+        }
+    }
+}
+
+
+void Foam::basicSpecieMixture::normalise()
+{
+    if (species_.size())
+    {
+        tmp<volScalarField> tYt
+        (
+            volScalarField::New
+            (
+                IOobject::groupName("Yt", phaseName_),
+                Y_[0].mesh(),
+                dimensionedScalar(dimless, 0)
+            )
+        );
+        volScalarField& Yt = tYt.ref();
+
+        forAll(Y_, i)
+        {
+            if (solve(i))
+            {
+                Y_[i].max(scalar(0));
+                Yt += Y_[i];
+            }
+        }
+
+        Y_[defaultSpecieIndex_] = scalar(1) - Yt;
+        Y_[defaultSpecieIndex_].max(scalar(0));
+    }
 }
 
 
diff --git a/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.H b/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.H
index ffd4c9a5cb..603e765816 100644
--- a/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.H
+++ b/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixture.H
@@ -59,9 +59,21 @@ protected:
 
     // Protected data
 
+        //- Phase-name
+        const word& phaseName_;
+
         //- Table of specie names
         speciesTable species_;
 
+        //- The name of the default specie
+        //  The mass fraction of which is derived from the other species
+        //  rather than solved.
+        //  Also used as the carrier specie in multicomponent diffusion
+        word defaultSpecie_;
+
+        //- The index of the default specie
+        label defaultSpecieIndex_;
+
         //- List of specie active flags
         mutable List<bool> active_;
 
@@ -69,6 +81,12 @@ protected:
         PtrList<volScalarField> Y_;
 
 
+    // Protected Member Functions
+
+        //- Scale the mass fractions to sum to 1
+        void correctMassFractions();
+
+
 public:
 
     //- Run time type information
@@ -103,6 +121,9 @@ public:
         //- Does the mixture include this specie?
         inline bool contains(const word& specieName) const;
 
+        //- Return the index of the default specie
+        inline label defaultSpecie() const;
+
         //- Return true for active species
         inline bool active(label speciei) const;
 
@@ -115,6 +136,10 @@ public:
         //- Set speciei inactive
         inline void setInactive(label speciei) const;
 
+        //- Return true if the specie should be solved for
+        //  i.e. active and not the default specie
+        inline bool solve(label speciei) const;
+
         //- Return the mass-fraction fields
         inline PtrList<volScalarField>& Y();
 
@@ -133,6 +158,11 @@ public:
         //- Return the const mass-fraction field for a specie given by name
         inline const volScalarField& Y(const word& specieName) const;
 
+        //- Normalise the mass fractions
+        //  by clipping positive
+        //  and deriving the default specie mass fraction from the other species
+        void normalise();
+
 
         // Specie properties
 
diff --git a/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixtureI.H b/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixtureI.H
index 2a1441e4d2..0a69694f96 100644
--- a/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixtureI.H
+++ b/src/thermophysicalModels/reactionThermo/mixtures/basicSpecieMixture/basicSpecieMixtureI.H
@@ -35,6 +35,12 @@ inline bool Foam::basicSpecieMixture::contains(const word& specieName) const
 }
 
 
+inline Foam::label Foam::basicSpecieMixture::defaultSpecie() const
+{
+    return defaultSpecieIndex_;
+}
+
+
 inline bool Foam::basicSpecieMixture::active(label speciei) const
 {
     return active_[speciei];
@@ -61,6 +67,12 @@ inline void Foam::basicSpecieMixture::setInactive(label speciei) const
 }
 
 
+inline bool Foam::basicSpecieMixture::solve(label speciei) const
+{
+    return speciei != defaultSpecieIndex_ && active_[speciei];
+}
+
+
 inline Foam::PtrList<Foam::volScalarField>& Foam::basicSpecieMixture::Y()
 {
     return Y_;
diff --git a/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.C b/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.C
index 51ecc30c56..2d429b6880 100644
--- a/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.C
+++ b/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.C
@@ -104,31 +104,6 @@ Foam::multiComponentMixture<ThermoType>::readSpeciesComposition
 }
 
 
-template<class ThermoType>
-void Foam::multiComponentMixture<ThermoType>::correctMassFractions()
-{
-    // Multiplication by 1.0 changes Yt patches to "calculated"
-    volScalarField Yt("Yt", 1.0*Y_[0]);
-
-    for (label n=1; n<Y_.size(); n++)
-    {
-        Yt += Y_[n];
-    }
-
-    if (mag(max(Yt).value()) < rootVSmall)
-    {
-        FatalErrorInFunction
-            << "Sum of mass fractions is zero for species " << this->species()
-            << exit(FatalError);
-    }
-
-    forAll(Y_, n)
-    {
-        Y_[n] /= Yt;
-    }
-}
-
-
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class ThermoType>
diff --git a/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.H b/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.H
index 559b008221..90595fadfc 100644
--- a/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.H
+++ b/src/thermophysicalModels/reactionThermo/mixtures/multiComponentMixture/multiComponentMixture.H
@@ -85,9 +85,6 @@ private:
             const speciesTable& speciesTable_
         ) const;
 
-        //- Correct the mass fractions to sum to 1
-        void correctMassFractions();
-
 
 public:
 
diff --git a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/Allrun b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/Allrun
index 4cb711ced9..bb2a842a71 100755
--- a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/Allrun
+++ b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/Allrun
@@ -14,7 +14,7 @@ setInertY()
     y=${1%.*}
     phase=${1#*.}
     [ $y != "none" ] && arg="-set $y" || arg="-remove"
-    runApplication -a foamDictionary -entry inertSpecie $arg \
+    runApplication -a foamDictionary -entry defaultSpecie $arg \
         constant/thermophysicalProperties.$phase
 }
 
diff --git a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.gas.orig b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.gas.orig
index 6e29af11df..de04f92378 100644
--- a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.gas.orig
+++ b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.gas.orig
@@ -33,7 +33,7 @@ species
     C3H8O
 );
 
-inertSpecie air;
+defaultSpecie air;
 
 air
 {
diff --git a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.liquid.orig b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.liquid.orig
index 6d4662efda..ad11057f6d 100644
--- a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.liquid.orig
+++ b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterAndIsopropanolEvaporation/constant/thermophysicalProperties.liquid.orig
@@ -32,7 +32,7 @@ species
     C3H8O
 );
 
-inertSpecie H2O;
+defaultSpecie H2O;
 
 H2O
 {
diff --git a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/Allrun b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/Allrun
index c0a2ab843b..4cbcc40d5a 100755
--- a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/Allrun
+++ b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/Allrun
@@ -18,7 +18,7 @@ setInertY()
         * ) arg="-set $y";;
     esac
 
-    runApplication -a foamDictionary -entry inertSpecie $arg \
+    runApplication -a foamDictionary -entry defaultSpecie $arg \
         constant/thermophysicalProperties.$phase
 }
 
diff --git a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/constant/thermophysicalProperties.gas.orig b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/constant/thermophysicalProperties.gas.orig
index 02c26c95b0..ec7de1d9fa 100644
--- a/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/constant/thermophysicalProperties.gas.orig
+++ b/test/multiphase/multiphaseEulerFoam/interfaceComposition/waterEvaporation/constant/thermophysicalProperties.gas.orig
@@ -26,7 +26,7 @@ thermoType
     energy          sensibleInternalEnergy;
 }
 
-inertSpecie air;
+defaultSpecie air;
 
 species
 (
diff --git a/tutorials/combustion/chemFoam/gri/constant/thermophysicalProperties b/tutorials/combustion/chemFoam/gri/constant/thermophysicalProperties
index 8cfb15e5bd..d0681f3e04 100644
--- a/tutorials/combustion/chemFoam/gri/constant/thermophysicalProperties
+++ b/tutorials/combustion/chemFoam/gri/constant/thermophysicalProperties
@@ -26,6 +26,8 @@ thermoType
     specie          specie;
 }
 
+defaultSpecie N2;
+
 #include "speciesThermo"
 
 // ************************************************************************* //
diff --git a/tutorials/combustion/chemFoam/h2/constant/thermophysicalProperties b/tutorials/combustion/chemFoam/h2/constant/thermophysicalProperties
index 8cfb15e5bd..d0681f3e04 100644
--- a/tutorials/combustion/chemFoam/h2/constant/thermophysicalProperties
+++ b/tutorials/combustion/chemFoam/h2/constant/thermophysicalProperties
@@ -26,6 +26,8 @@ thermoType
     specie          specie;
 }
 
+defaultSpecie N2;
+
 #include "speciesThermo"
 
 // ************************************************************************* //
diff --git a/tutorials/combustion/chemFoam/ic8h18/constant/thermophysicalProperties b/tutorials/combustion/chemFoam/ic8h18/constant/thermophysicalProperties
index 8cfb15e5bd..d0681f3e04 100644
--- a/tutorials/combustion/chemFoam/ic8h18/constant/thermophysicalProperties
+++ b/tutorials/combustion/chemFoam/ic8h18/constant/thermophysicalProperties
@@ -26,6 +26,8 @@ thermoType
     specie          specie;
 }
 
+defaultSpecie N2;
+
 #include "speciesThermo"
 
 // ************************************************************************* //
diff --git a/tutorials/combustion/chemFoam/ic8h18_TDAC/constant/thermophysicalProperties b/tutorials/combustion/chemFoam/ic8h18_TDAC/constant/thermophysicalProperties
index 8cfb15e5bd..d0681f3e04 100644
--- a/tutorials/combustion/chemFoam/ic8h18_TDAC/constant/thermophysicalProperties
+++ b/tutorials/combustion/chemFoam/ic8h18_TDAC/constant/thermophysicalProperties
@@ -26,6 +26,8 @@ thermoType
     specie          specie;
 }
 
+defaultSpecie N2;
+
 #include "speciesThermo"
 
 // ************************************************************************* //
diff --git a/tutorials/combustion/chemFoam/nc7h16/constant/thermophysicalProperties b/tutorials/combustion/chemFoam/nc7h16/constant/thermophysicalProperties
index 8cfb15e5bd..d0681f3e04 100644
--- a/tutorials/combustion/chemFoam/nc7h16/constant/thermophysicalProperties
+++ b/tutorials/combustion/chemFoam/nc7h16/constant/thermophysicalProperties
@@ -26,6 +26,8 @@ thermoType
     specie          specie;
 }
 
+defaultSpecie N2;
+
 #include "speciesThermo"
 
 // ************************************************************************* //
diff --git a/tutorials/combustion/coldEngineFoam/freePiston/constant/thermophysicalProperties b/tutorials/combustion/coldEngineFoam/freePiston/constant/thermophysicalProperties
index e634343da6..9d36d09853 100644
--- a/tutorials/combustion/coldEngineFoam/freePiston/constant/thermophysicalProperties
+++ b/tutorials/combustion/coldEngineFoam/freePiston/constant/thermophysicalProperties
@@ -31,7 +31,7 @@ species
     air
 );
 
-inertSpecie air;
+defaultSpecie air;
 
 #include "include/thermo.air"
 
diff --git a/tutorials/combustion/fireFoam/LES/smallPoolFire2D/constant/thermophysicalProperties b/tutorials/combustion/fireFoam/LES/smallPoolFire2D/constant/thermophysicalProperties
index d8de1362ea..41791c94ed 100644
--- a/tutorials/combustion/fireFoam/LES/smallPoolFire2D/constant/thermophysicalProperties
+++ b/tutorials/combustion/fireFoam/LES/smallPoolFire2D/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 fuel        CH4;
 
diff --git a/tutorials/combustion/fireFoam/LES/smallPoolFire3D/constant/thermophysicalProperties b/tutorials/combustion/fireFoam/LES/smallPoolFire3D/constant/thermophysicalProperties
index d8de1362ea..41791c94ed 100644
--- a/tutorials/combustion/fireFoam/LES/smallPoolFire3D/constant/thermophysicalProperties
+++ b/tutorials/combustion/fireFoam/LES/smallPoolFire3D/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 fuel        CH4;
 
diff --git a/tutorials/combustion/reactingFoam/RAS/DLR_A_LTS/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/RAS/DLR_A_LTS/constant/thermophysicalProperties
index b689ee9664..e22ce8c94c 100644
--- a/tutorials/combustion/reactingFoam/RAS/DLR_A_LTS/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/RAS/DLR_A_LTS/constant/thermophysicalProperties
@@ -27,7 +27,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGasGRI"
 
diff --git a/tutorials/combustion/reactingFoam/RAS/SandiaD_LTS/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/RAS/SandiaD_LTS/constant/thermophysicalProperties
index 8330b61360..2c6d73966f 100644
--- a/tutorials/combustion/reactingFoam/RAS/SandiaD_LTS/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/RAS/SandiaD_LTS/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGasGRI"
 
diff --git a/tutorials/combustion/reactingFoam/RAS/membrane/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/RAS/membrane/constant/thermophysicalProperties
index 816e936a8d..96037aacb8 100644
--- a/tutorials/combustion/reactingFoam/RAS/membrane/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/RAS/membrane/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGas"
 
diff --git a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D/constant/thermophysicalProperties
index 816e936a8d..96037aacb8 100644
--- a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGas"
 
diff --git a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS/constant/thermophysicalProperties
index 816e936a8d..96037aacb8 100644
--- a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGas"
 
diff --git a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS_GRI_TDAC/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS_GRI_TDAC/constant/thermophysicalProperties
index 8330b61360..2c6d73966f 100644
--- a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS_GRI_TDAC/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2DLTS_GRI_TDAC/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGasGRI"
 
diff --git a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI/constant/thermophysicalProperties
index 8330b61360..2c6d73966f 100644
--- a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGasGRI"
 
diff --git a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI_TDAC/constant/thermophysicalProperties b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI_TDAC/constant/thermophysicalProperties
index 8330b61360..2c6d73966f 100644
--- a/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI_TDAC/constant/thermophysicalProperties
+++ b/tutorials/combustion/reactingFoam/laminar/counterFlowFlame2D_GRI_TDAC/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGasGRI"
 
diff --git a/tutorials/heatTransfer/chtMultiRegionFoam/reverseBurner/constant/gas/thermophysicalProperties b/tutorials/heatTransfer/chtMultiRegionFoam/reverseBurner/constant/gas/thermophysicalProperties
index 8779e3be95..24ace2b3ca 100644
--- a/tutorials/heatTransfer/chtMultiRegionFoam/reverseBurner/constant/gas/thermophysicalProperties
+++ b/tutorials/heatTransfer/chtMultiRegionFoam/reverseBurner/constant/gas/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     energy          sensibleEnthalpy;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGas"
 
diff --git a/tutorials/lagrangian/buoyantReactingParticleFoam/cylinder/constant/thermophysicalProperties b/tutorials/lagrangian/buoyantReactingParticleFoam/cylinder/constant/thermophysicalProperties
index 52f895213e..f2a088505d 100644
--- a/tutorials/lagrangian/buoyantReactingParticleFoam/cylinder/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/buoyantReactingParticleFoam/cylinder/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/buoyantReactingParticleFoam/hotBoxes/constant/thermophysicalProperties b/tutorials/lagrangian/buoyantReactingParticleFoam/hotBoxes/constant/thermophysicalProperties
index 52f895213e..f2a088505d 100644
--- a/tutorials/lagrangian/buoyantReactingParticleFoam/hotBoxes/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/buoyantReactingParticleFoam/hotBoxes/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/buoyantReactingParticleFoam/rivuletPanel/constant/thermophysicalProperties b/tutorials/lagrangian/buoyantReactingParticleFoam/rivuletPanel/constant/thermophysicalProperties
index 52f895213e..f2a088505d 100644
--- a/tutorials/lagrangian/buoyantReactingParticleFoam/rivuletPanel/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/buoyantReactingParticleFoam/rivuletPanel/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/buoyantReactingParticleFoam/splashPanel/constant/thermophysicalProperties b/tutorials/lagrangian/buoyantReactingParticleFoam/splashPanel/constant/thermophysicalProperties
index 52f895213e..f2a088505d 100644
--- a/tutorials/lagrangian/buoyantReactingParticleFoam/splashPanel/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/buoyantReactingParticleFoam/splashPanel/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/reactingParticleFoam/aachenBomb/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/aachenBomb/constant/thermophysicalProperties
index 7af9a29ccf..e9261d6fde 100644
--- a/tutorials/lagrangian/reactingParticleFoam/aachenBomb/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/aachenBomb/constant/thermophysicalProperties
@@ -30,7 +30,7 @@ thermoType
 
 newFormat       yes;
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/reactingParticleFoam/counterFlowFlame2DLTS/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/counterFlowFlame2DLTS/constant/thermophysicalProperties
index e5fc4a91ad..de94aa2e98 100644
--- a/tutorials/lagrangian/reactingParticleFoam/counterFlowFlame2DLTS/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/counterFlowFlame2DLTS/constant/thermophysicalProperties
@@ -26,7 +26,7 @@ thermoType
     specie          specie;
 }
 
-inertSpecie N2;
+defaultSpecie N2;
 
 #include "thermo.compressibleGas"
 
diff --git a/tutorials/lagrangian/reactingParticleFoam/filter/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/filter/constant/thermophysicalProperties
index 52f895213e..f2a088505d 100644
--- a/tutorials/lagrangian/reactingParticleFoam/filter/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/filter/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/reactingParticleFoam/parcelInBox/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/parcelInBox/constant/thermophysicalProperties
index 6d04b522ce..6e3bcf41ec 100644
--- a/tutorials/lagrangian/reactingParticleFoam/parcelInBox/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/parcelInBox/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     air;
+defaultSpecie     air;
 
 liquids
 {
diff --git a/tutorials/lagrangian/reactingParticleFoam/simplifiedSiwek/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/simplifiedSiwek/constant/thermophysicalProperties
index 53762b8e10..e1987d78fd 100644
--- a/tutorials/lagrangian/reactingParticleFoam/simplifiedSiwek/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/simplifiedSiwek/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     N2;
+defaultSpecie     N2;
 
 liquids
 {
diff --git a/tutorials/lagrangian/reactingParticleFoam/verticalChannel/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/verticalChannel/constant/thermophysicalProperties
index 6d04b522ce..6e3bcf41ec 100644
--- a/tutorials/lagrangian/reactingParticleFoam/verticalChannel/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/verticalChannel/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     air;
+defaultSpecie     air;
 
 liquids
 {
diff --git a/tutorials/lagrangian/reactingParticleFoam/verticalChannelLTS/constant/thermophysicalProperties b/tutorials/lagrangian/reactingParticleFoam/verticalChannelLTS/constant/thermophysicalProperties
index 6d04b522ce..6e3bcf41ec 100644
--- a/tutorials/lagrangian/reactingParticleFoam/verticalChannelLTS/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/reactingParticleFoam/verticalChannelLTS/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     air;
+defaultSpecie     air;
 
 liquids
 {
diff --git a/tutorials/lagrangian/simpleReactingParticleFoam/verticalChannel/constant/thermophysicalProperties b/tutorials/lagrangian/simpleReactingParticleFoam/verticalChannel/constant/thermophysicalProperties
index 6d04b522ce..6e3bcf41ec 100644
--- a/tutorials/lagrangian/simpleReactingParticleFoam/verticalChannel/constant/thermophysicalProperties
+++ b/tutorials/lagrangian/simpleReactingParticleFoam/verticalChannel/constant/thermophysicalProperties
@@ -28,7 +28,7 @@ thermoType
 
 #include "speciesThermo"
 
-inertSpecie     air;
+defaultSpecie     air;
 
 liquids
 {
diff --git a/tutorials/multiphase/multiphaseEulerFoam/RAS/bubbleColumnEvaporatingReacting/constant/thermophysicalProperties.gas b/tutorials/multiphase/multiphaseEulerFoam/RAS/bubbleColumnEvaporatingReacting/constant/thermophysicalProperties.gas
index 18a1db6b89..cde8b0d5a8 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/RAS/bubbleColumnEvaporatingReacting/constant/thermophysicalProperties.gas
+++ b/tutorials/multiphase/multiphaseEulerFoam/RAS/bubbleColumnEvaporatingReacting/constant/thermophysicalProperties.gas
@@ -26,7 +26,7 @@ thermoType
     energy          sensibleInternalEnergy;
 }
 
-inertSpecie AIR;
+defaultSpecie AIR;
 
 #include "thermo.gas"
 
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.gas b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.gas
index 02c26c95b0..ec7de1d9fa 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.gas
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.gas
@@ -26,7 +26,7 @@ thermoType
     energy          sensibleInternalEnergy;
 }
 
-inertSpecie air;
+defaultSpecie air;
 
 species
 (
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.liquid b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.liquid
index 8e6b77c05d..cc0ae5b2ba 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.liquid
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporating/constant/thermophysicalProperties.liquid
@@ -32,7 +32,7 @@ species
     H2O
 );
 
-inertSpecie H2O;
+defaultSpecie H2O;
 
 "(mixture|H2O)"
 {
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.gas b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.gas
index 97bddfccdf..da2b4786ca 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.gas
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.gas
@@ -32,7 +32,7 @@ species
     water
 );
 
-inertSpecie air;
+defaultSpecie air;
 
 "(mixture|air)"
 {
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.liquid b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.liquid
index 8efb582c65..7da896559d 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.liquid
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/bubbleColumnEvaporatingDissolving/constant/thermophysicalProperties.liquid
@@ -32,7 +32,7 @@ species
     water
 );
 
-inertSpecie water;
+defaultSpecie water;
 
 "(mixture|water)"
 {
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.particles b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.particles
index d50f1712fc..21a24e1de1 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.particles
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.particles
@@ -28,7 +28,7 @@ thermoType
 
 species (TiO2);
 
-inertSpecie TiO2;
+defaultSpecie TiO2;
 
 TiO2
 {
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.vapor b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.vapor
index 1a8c5f4b10..20cf783c29 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.vapor
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesis/constant/thermophysicalProperties.vapor
@@ -26,7 +26,7 @@ thermoType
     energy          sensibleEnthalpy;
 }
 
-inertSpecie Ar;
+defaultSpecie Ar;
 
 #include "$FOAM_CASE/constant/thermo.vapor"
 
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.particles b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.particles
index 1673e35ccc..37a815421f 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.particles
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.particles
@@ -28,7 +28,7 @@ thermoType
 
 species (TiO2 TiO2_s);
 
-inertSpecie TiO2;
+defaultSpecie TiO2;
 
 TiO2
 {
diff --git a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.vapor b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.vapor
index 1a8c5f4b10..20cf783c29 100644
--- a/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.vapor
+++ b/tutorials/multiphase/multiphaseEulerFoam/laminar/titaniaSynthesisSurface/constant/thermophysicalProperties.vapor
@@ -26,7 +26,7 @@ thermoType
     energy          sensibleEnthalpy;
 }
 
-inertSpecie Ar;
+defaultSpecie Ar;
 
 #include "$FOAM_CASE/constant/thermo.vapor"