VEN124 - Introduction to Wine Production
Author: Linda F. Bisson, UC Davis
Section 5 - Post-Fermentation Processing
Lecture 15: Chemical and Molecular Stability of Wine and Wine Fining
Lecture 15: Chemical and Molecular Stability of Wine and Wine Fining
It is important that the wine be stabilized against unwanted changes prior to bottling. Those changes may
be chemical in nature, or due to macromolecular interactions and changes in solubility. Microbial stability
is also an important issue and will be the subject of lesson 16.
be chemical in nature, or due to macromolecular interactions and changes in solubility. Microbial stability
is also an important issue and will be the subject of lesson 16.
Stability
GOAL: to stabilize the clarity and desirable sensory characteristics
One objective of wine finishing processes is to stabilize both the clarity of the wine as well as desirable
sensory characteristics. There are three types of problems that can impact the clarity of a wine
post-fermentation.
sensory characteristics. There are three types of problems that can impact the clarity of a wine
post-fermentation.
| Stability: Types of Problems | ||
| • Chemical stability | ||
| • Macromolecular stability | ||
| • Microbial stability | ||
Loss of clarity can come from three sources: microbial growth and production of polysaccharides;
precipitation of chemical compounds and denaturation and complex formation between
macromolecules (proteins, polysaccharides and polyphenolics).
precipitation of chemical compounds and denaturation and complex formation between
macromolecules (proteins, polysaccharides and polyphenolics).
I. The Chemical Instability of Wines
There are several chemical components of wine that may change over time to form precipitates
or hazes. Hazes are also called “casse” when caused by high concentrations of metal ions. These
instabilities are generally visual defects. Other types of chemical reactions can cause off-odors
and flavors to form and are generally referred to as the appearance of oxidation products or
aging character.
or hazes. Hazes are also called “casse” when caused by high concentrations of metal ions. These
instabilities are generally visual defects. Other types of chemical reactions can cause off-odors
and flavors to form and are generally referred to as the appearance of oxidation products or
aging character.
| Chemical Instabilities: | ||
| • Metal Ions | ||
| • Tartrate | ||
| • Polymerized Phenols | ||
| • Oxidation Products | ||
| Chemical Instabilities: Metal ions | ||
| • Fe and Cu can form a precipitate "casse" | ||
| • Caused by use of iron or copper containing materials in winery or from pesticides | ||
| • Elimination: Ferrocyanide precipitation (not legal everywhere) | ||
Metal ions can catalyze the formation of spoilage characters as well as lead to the formation
of a haze or "casse". Current industry practice is to use tank and line materials that do not
lead to the presence of metal ions in the wine. Copper can come from the use of
copper-containing fungicides. Casse formation is virtually unheard of in California wine
production. Copper in the presence of sulfite will form colloidal copper sulfide, which will
react with proteins forming a brownish-red sediment. Metal ions can be removed from
wine by fining, using cation exchangers and other methods. Removal of the protein
of wine also prevents casse formation. It is important to note if the technique being used
to eliminate a problem is a legal treatment. Not all treatments are allowed in all countries.
of a haze or "casse". Current industry practice is to use tank and line materials that do not
lead to the presence of metal ions in the wine. Copper can come from the use of
copper-containing fungicides. Casse formation is virtually unheard of in California wine
production. Copper in the presence of sulfite will form colloidal copper sulfide, which will
react with proteins forming a brownish-red sediment. Metal ions can be removed from
wine by fining, using cation exchangers and other methods. Removal of the protein
of wine also prevents casse formation. It is important to note if the technique being used
to eliminate a problem is a legal treatment. Not all treatments are allowed in all countries.
| Chemical Instabilities: Tartrate | ||
| • At low temperature, tartrate will crystallize | ||
| • Mistaken for ground glass by consumers | ||
| • Unstable in presence of Ca2+ | ||
| • Solubility depends upon pH, K+, tartrate concentrations | ||
| • Can get co-crystallization with other organic acids | ||
Another source of chemical instability is the major grape acid tartrate. Tartrate can form
crystals during aging of a wine. This is typically seen as the glass-like crystals that
form on the surface of the cork. They are harmless, but frequently confused with
ground glass by consumers so it is considered a potential problem that must be prevented
from happening in the bottle. Several factors influence the precipitation of tartrate. Crystal
formation may be catalyzed by the presence of cations like calcium, and it may be
nucleated by addition of tartrate crystals (cream of tartar). Solubility of tartrate is
also dependent upon the pH and potassium ion concentrations. It is also a function of
the concentration of the anionic species and of other acid species as co-crystallization
may occur.
crystals during aging of a wine. This is typically seen as the glass-like crystals that
form on the surface of the cork. They are harmless, but frequently confused with
ground glass by consumers so it is considered a potential problem that must be prevented
from happening in the bottle. Several factors influence the precipitation of tartrate. Crystal
formation may be catalyzed by the presence of cations like calcium, and it may be
nucleated by addition of tartrate crystals (cream of tartar). Solubility of tartrate is
also dependent upon the pH and potassium ion concentrations. It is also a function of
the concentration of the anionic species and of other acid species as co-crystallization
may occur.
| Tartrate: The Solution | ||
| • Super-chill wine to catalyze crystallization | ||
| • Nucleate process with tartrate crystals | ||
| • Add cations to initiate crystallization | ||
Temperature also affects solubility, so a common method for catalyzing tartrate
precipitation is super-chilling of the wine. The process can also be initiated by addition
of cations or crystals.
precipitation is super-chilling of the wine. The process can also be initiated by addition
of cations or crystals.
| Chemical Instabilities: Polymerized Phenols | ||
| • Can precipitate during aging | ||
| • Undesired in bottle | ||
A precipitate or sediment may also form from the polymerization of phenolic
compounds. During aging of the wine a sediment will form. The sediment will coat the
surface of the glass of the bottle if the wine is bottled prior to achieving phenolic
stability. The exact composition of this material is not known, but it is likely mainly
a mixture of tannin and protein. It is more common in red wines of moderate phenolic
content that have not been aged in oak. Other compounds may also yield sediments.
compounds. During aging of the wine a sediment will form. The sediment will coat the
surface of the glass of the bottle if the wine is bottled prior to achieving phenolic
stability. The exact composition of this material is not known, but it is likely mainly
a mixture of tannin and protein. It is more common in red wines of moderate phenolic
content that have not been aged in oak. Other compounds may also yield sediments.
| Chemical Instabilities: Oxidation Products | |||
| • Off-color | |||
| Brown | |||
| Pink | |||
| Orange | |||
| • Off-characters | |||
| Aldehydes | |||
| Prevented by using antioxidants | |||
Undesired oxidation products may also form in wine during aging. Off-colors may
form from the oxidation reactions. Browning occurs from the oxidation of phenolic
compounds. There are several ways in which brown pigments may be formed, as
discussed in the textbook. Pinking is obviously a problem only in white wines as
this off-color is undetectable in reds. It has been suggested that the pink character
is derived from the oxidation of leucocyanidin to cyanidin, but several studies
suggest that this is not the pink compound formed. The orange character is rare,
and the source of the off-color is not known. Aldehyde also forms from the oxidation
of phenolic compounds and will be discussed in the lecture on aging. Oxidative
defects can be prevented by the use of antioxidants such as SO2 and ascorbic acid,
or fining agents such as PVPP that eliminates the "pinking potential".
form from the oxidation reactions. Browning occurs from the oxidation of phenolic
compounds. There are several ways in which brown pigments may be formed, as
discussed in the textbook. Pinking is obviously a problem only in white wines as
this off-color is undetectable in reds. It has been suggested that the pink character
is derived from the oxidation of leucocyanidin to cyanidin, but several studies
suggest that this is not the pink compound formed. The orange character is rare,
and the source of the off-color is not known. Aldehyde also forms from the oxidation
of phenolic compounds and will be discussed in the lecture on aging. Oxidative
defects can be prevented by the use of antioxidants such as SO2 and ascorbic acid,
or fining agents such as PVPP that eliminates the "pinking potential".
II. Macromolecular Instability in Wine
The macromolecule proteins and polysaccharides found in wine can form complexes
in wine leading to the appearance of a visible haze.
in wine leading to the appearance of a visible haze.
| Macromolecular Stability: | ||
| • Protein | ||
| • Polysaccharides | ||
| Macromolecular Stability: Protein Instability | ||
| • Proteins involved are from grapes | ||
| • Denature over time causing visible haze | ||
| • Hydrophobic regions interact | ||
| • Agglutination complexes formed | ||
| • Complex becomes visible | ||
| • Accelerated by treatment of wine at high temperature (HTST) | ||
| • Can be prevented by fining | ||
Over time proteins will denature in wine exposing hydrophobic groups. The hydrophobic
groups will interact with other hydrophobic material in the wine leading to aggregation
and production of cloudiness. There is not a good correlation between total protein
content and haze formation, as a subset of the proteins of wine appears to catalyze
this process. Protein denaturation is complex and a function of the temperature to
which the wine has been exposed, the pH, and the composition of the wine. The proteins
causing haze are derived from the grape, not from microbial activity. Protein
denaturation is accelerated at higher temperatures. The fining agent bentonite can
be used to remove protein from wine, eliminating the "haze forming potential". HTST
treatments remove significant amounts of protein but lead to the formation of a
bentonite-resistant haze. This may be due to the fact that protective colloidal materials
have also been removed.
groups will interact with other hydrophobic material in the wine leading to aggregation
and production of cloudiness. There is not a good correlation between total protein
content and haze formation, as a subset of the proteins of wine appears to catalyze
this process. Protein denaturation is complex and a function of the temperature to
which the wine has been exposed, the pH, and the composition of the wine. The proteins
causing haze are derived from the grape, not from microbial activity. Protein
denaturation is accelerated at higher temperatures. The fining agent bentonite can
be used to remove protein from wine, eliminating the "haze forming potential". HTST
treatments remove significant amounts of protein but lead to the formation of a
bentonite-resistant haze. This may be due to the fact that protective colloidal materials
have also been removed.
| HTST: | ||
| • "High Temperature Short Time" | ||
| • Used on juices with high oxidase levels | ||
| • Polyphenol oxidase from plant | ||
| • Laccase from Botrytis | ||
| • Used on wines | ||
| • Pasteurization (Kosher wines) | ||
| • Inactivation of added enzymatic activity | ||
HTST treatments are used to eliminate laccase activity in white wines. Heat
treatments are also used in the pasteurization of wines, which results in similar haze
problems. Protein hazes are largely comprised of protein but can also contain phenolic
compounds and polysaccharides. Polysaccharide hazes may also form. These
hazes are largely comprised of polysaccharide but can contain some protein and
polyphenolic material. A quick test that we use to distinguish between the two
is to evaluate the solubility of the particulate matter in hot water. Denatured
proteins are not soluble under these conditions, but polysaccharide will go back
into solution due to the increase in temperature and reduction in ethanol content
of the medium. Chemical assays can also be used to distinguish between the two.
treatments are also used in the pasteurization of wines, which results in similar haze
problems. Protein hazes are largely comprised of protein but can also contain phenolic
compounds and polysaccharides. Polysaccharide hazes may also form. These
hazes are largely comprised of polysaccharide but can contain some protein and
polyphenolic material. A quick test that we use to distinguish between the two
is to evaluate the solubility of the particulate matter in hot water. Denatured
proteins are not soluble under these conditions, but polysaccharide will go back
into solution due to the increase in temperature and reduction in ethanol content
of the medium. Chemical assays can also be used to distinguish between the two.
| Macromolecular Stability: Polysaccharide Instability | ||
| • Polysaccharides come from either plant or microbial activity | ||
| • Insoluble at high ethanol causing visible haze | ||
| • Insoluble at low temperatures | ||
| • More difficult to prevent/remove | ||
Polysaccharides may derive from the plant or from microbial activity. Plant
polysaccharide content is high under conditions leading to maceration of the skins.
The microbial polysaccharides are produced by bacteria. Polysaccharides are insoluble
in ethanol, which is increased at low pH. In contrast to protein hazes,
fining agents effectively removing "polysaccharide haze forming potential" do not exist.
polysaccharide content is high under conditions leading to maceration of the skins.
The microbial polysaccharides are produced by bacteria. Polysaccharides are insoluble
in ethanol, which is increased at low pH. In contrast to protein hazes,
fining agents effectively removing "polysaccharide haze forming potential" do not exist.
III. The Fining Process
Particulate matter in solution deflects light making the solution appear hazy. The
goal of the clarification operations discussed previously is the removal of existing
cloudiness and sediment from a wine. This is obviously possible by the techniques
of centrifugation and filtration if the particulate matter is already present. Frequently,
however, the material that will form colloids and eventually agglutinate into particles
is in the wine in a soluble form as in the case of the chemical and macromolecular
components that can form hazes and precipitates. In this case it is necessary
to design operations to remove the "potential" for formation of a haze or
sediment. This may be accomplished by removing one or more of the participants
in colloid formation or the use of techniques to stabilize the colloids against agglutination.
The latter approach is more risky than the former.
goal of the clarification operations discussed previously is the removal of existing
cloudiness and sediment from a wine. This is obviously possible by the techniques
of centrifugation and filtration if the particulate matter is already present. Frequently,
however, the material that will form colloids and eventually agglutinate into particles
is in the wine in a soluble form as in the case of the chemical and macromolecular
components that can form hazes and precipitates. In this case it is necessary
to design operations to remove the "potential" for formation of a haze or
sediment. This may be accomplished by removing one or more of the participants
in colloid formation or the use of techniques to stabilize the colloids against agglutination.
The latter approach is more risky than the former.
| Stabilization of Colloidal Particles | |
 |
Fining refers to the addition of an adsorptive agent to wine or juice followed by settling
or precipitation of the agent. Undesired wine components bind to and then settle with
the fining agent and are thereby removed from the wine. As discussed below there are
several different types of fining agents. In some wines it may be necessary to use
more than one agent. Other wines might not benefit from fining at all. Many fining
agents are not highly specific, meaning that if not appropriately used, positive and well
as undesired characters may be removed from the wine. Fining can also be used
to accelerate the conversion of colloidal substances into agglutinated complexes so
that clarification processes can be used to remove the particulate matter. It
is important that the winemaker understand the uses of fining agents to avoid
unwarranted treatment of the wine.
or precipitation of the agent. Undesired wine components bind to and then settle with
the fining agent and are thereby removed from the wine. As discussed below there are
several different types of fining agents. In some wines it may be necessary to use
more than one agent. Other wines might not benefit from fining at all. Many fining
agents are not highly specific, meaning that if not appropriately used, positive and well
as undesired characters may be removed from the wine. Fining can also be used
to accelerate the conversion of colloidal substances into agglutinated complexes so
that clarification processes can be used to remove the particulate matter. It
is important that the winemaker understand the uses of fining agents to avoid
unwarranted treatment of the wine.
Goal of Fining:
Removal of soluble components that are undesired stylistically or that will
lead to an instability.
lead to an instability.
Fining can therefore be used to remove components that will result in instability
of the wine or that are simply undesired from a stylistic perspective. This
includes removal of proteins that would otherwise result in formation of a haze,
tannins or phenolic compounds reducing astringency and bitterness, off-colors or
off-color forming potential, metal ions, or off-flavors and aromas. Fining can also
be used to add nuances, depending upon the agent used.
of the wine or that are simply undesired from a stylistic perspective. This
includes removal of proteins that would otherwise result in formation of a haze,
tannins or phenolic compounds reducing astringency and bitterness, off-colors or
off-color forming potential, metal ions, or off-flavors and aromas. Fining can also
be used to add nuances, depending upon the agent used.
| Components to Be Removed | ||
| • Protein: "haze-forming potential" | ||
| • Phenolic compounds (tannin): soften wine by reducing bitterness and astringency | ||
| • Metal ions | ||
| • Off-character or off-character-forming potential | ||
The winemaker should carefully consider what agents will be used and in what order. It is
important to conduct fining operations before clarification processes since some residual
fining agents may impact wine clarity. Some clarification or fining treatments may
lay lead to a destabilization of another component of the wine, so this must be taken
into account. For example, it is thought that wine polysaccharides can coat the
surface of colloidal protein-tannin complexes preventing those complexes from further
agglutination and haze formation. Disruption of the coating effect of the polysaccharides
will lead to the appearance of a visible cloudiness of the wine. Also, some proteins are
stabilized by interactions ions on the hydrophilic or exposed surface of the protein.
Removal of those ions can lead to unfolding and denaturation of the protein, which
leads to colloid formation. Fining agents operate by taking advantage of hydrophobic
or hydrophilic interactions between the agent and the species to be removed. The fining
agents used are generally not soluble in wine or are of limited solubility. The agents
initially dissolve in the wine; interact with wine components then come out of solution
bringing wine components with them.
important to conduct fining operations before clarification processes since some residual
fining agents may impact wine clarity. Some clarification or fining treatments may
lay lead to a destabilization of another component of the wine, so this must be taken
into account. For example, it is thought that wine polysaccharides can coat the
surface of colloidal protein-tannin complexes preventing those complexes from further
agglutination and haze formation. Disruption of the coating effect of the polysaccharides
will lead to the appearance of a visible cloudiness of the wine. Also, some proteins are
stabilized by interactions ions on the hydrophilic or exposed surface of the protein.
Removal of those ions can lead to unfolding and denaturation of the protein, which
leads to colloid formation. Fining agents operate by taking advantage of hydrophobic
or hydrophilic interactions between the agent and the species to be removed. The fining
agents used are generally not soluble in wine or are of limited solubility. The agents
initially dissolve in the wine; interact with wine components then come out of solution
bringing wine components with them.
| Mechanism of Fining: | ||
| • Take advantage of either hydrophobic or hydrophilic interactions to remove offending component | ||
| • Wine will initially be cloudy, but particles will eventually become large and sink | ||
| • Clarify by racking or filtration | ||
| • Add a charged component that will interact with oppositely charged components followed by precipitation of the neutral complex | ||
| • Add a denaturing component that will expose hydrophobic surfaces that will then interact allowing a hydrophobic complex to form | ||
The wine generally has to undergo a clarification treatment following addition of the fining
agent. Components of one charge may be used to remove components of the opposite
charge. Due to the low pH wine proteins are generally positively charged and can be
removed by negatively charged fining agents. In this case, both the fining agent
and the component to be removed carry multiple charges. This allows a large insoluble
complex to form.
agent. Components of one charge may be used to remove components of the opposite
charge. Due to the low pH wine proteins are generally positively charged and can be
removed by negatively charged fining agents. In this case, both the fining agent
and the component to be removed carry multiple charges. This allows a large insoluble
complex to form.
| Fining: Charge Interactions | |
 |
Similarly, denaturation of proteins reveals non-polar regions or areas of hydrophobicity
that strongly interact with other hydrophobic regions due to Van der Waals forces.
Multiple domains are exposed capable of interaction with multiple components again
leading to the formation of a large lattice or complex. In some cases, more than one
agent is added. The first agent may be responsible for denaturation of the undesired
component allowing interaction with the stripping agent.
that strongly interact with other hydrophobic regions due to Van der Waals forces.
Multiple domains are exposed capable of interaction with multiple components again
leading to the formation of a large lattice or complex. In some cases, more than one
agent is added. The first agent may be responsible for denaturation of the undesired
component allowing interaction with the stripping agent.
| Fining: Hydrophobic Interactions | |
 |
IV. Choice of Fining Conditions
There are two important considerations in the choice of fining agents and conditions.
First, the impact of additions can be difficult to predict given the compositional
uncertainties of the wine. Therefore fining trials are critical to avoid unnecessary
treatments and over-fining. Second, it is important to understand the relationship
between the conditions of the trial and production conditions. The level and extent
of mixing will impact fining agent effectiveness, as will temperature and other factors.
It is unlikely those factors are accurately duplicated during bench scale trials. Although
more time consuming it is safer to add agents in doses rather than all at once and
to assess the impact on the wine after each incremental addition.
First, the impact of additions can be difficult to predict given the compositional
uncertainties of the wine. Therefore fining trials are critical to avoid unnecessary
treatments and over-fining. Second, it is important to understand the relationship
between the conditions of the trial and production conditions. The level and extent
of mixing will impact fining agent effectiveness, as will temperature and other factors.
It is unlikely those factors are accurately duplicated during bench scale trials. Although
more time consuming it is safer to add agents in doses rather than all at once and
to assess the impact on the wine after each incremental addition.
| Choice of Fining Conditions: | ||
| • Difficult to predict outcome due to complexity of process and number of unknowns | ||
| • Temperature influences process | ||
| • Amount and type of mixing critical | ||
| • Relative molecular weight and charge density of particles important for complex/lattice formation | ||
Fining is one of the most challenging of winemaking operations because the outcome is
difficult to predict. This is due to the fact that many variables impact component
solubility in wine and these variables are not easily measured.
difficult to predict. This is due to the fact that many variables impact component
solubility in wine and these variables are not easily measured.
Temperature has a striking effect as it impacts rates of denaturation and the
stability of complexes formed. At higher temperature denaturation or unfolding is
favored while at low temperature many components are less soluble so will more
likely precipitate. Since fining requires that the fining agent make direct contact
with the components to be removed, how the fining agent is prepared and
added to the wine is critical. It is also important to know that the undesired
component will not just interact with the fining agent but will be capable of
forming a lattice structure that will settle from the wine.
stability of complexes formed. At higher temperature denaturation or unfolding is
favored while at low temperature many components are less soluble so will more
likely precipitate. Since fining requires that the fining agent make direct contact
with the components to be removed, how the fining agent is prepared and
added to the wine is critical. It is also important to know that the undesired
component will not just interact with the fining agent but will be capable of
forming a lattice structure that will settle from the wine.
The efficiency of agglutination is also affected by the nature of the components
present in wine and their relative ratios. There is not a linear relationship between
total tannin content and protein content and colloid formation and agglutination.
Tannin protein interaction occurs more readily at lower pH values, so the pH of
the wine impacts stability of the complexes. Divalent as well as monovalent
cations can catalyze flocculation and precipitation of tannins. The nature and
content of polysaccharides is also important since these components can
both participate in and dampen colloidal interactions.
present in wine and their relative ratios. There is not a linear relationship between
total tannin content and protein content and colloid formation and agglutination.
Tannin protein interaction occurs more readily at lower pH values, so the pH of
the wine impacts stability of the complexes. Divalent as well as monovalent
cations can catalyze flocculation and precipitation of tannins. The nature and
content of polysaccharides is also important since these components can
both participate in and dampen colloidal interactions.
The purpose of this discussion is to underscore the importance of conducting fining
trials for each wine to be treated in the winery. This is generally done using small
volume lots from the wine to be treated. It is important to remember that small scale
or laboratory fining conditions may not mimic the actual behavior of agents on a
commercial scale due to difficulties in the speed or extent of mixing. However it is
possible to determine the relationship between small scale fining trial and commercial
scale fining. This need not be done every time a wine is fined. We have found
reasonable reproducibility in scaling up from a fining trial once the "scaling" factors
are understood. It is also possible to adapt the small scale fining trial (adjust
rates of agent addition and mixing) to match that of the commercial operation.
Under typical winery conditions this has to be done empirically, by measuring loss
of haze forming potential with step wise addition of an agent and repeating the
step wise addition under a commercial scale and comparing the amount of
undesired component (tannin, protein) remaining in the treated wine. This procedure
can also be used to test for the potential of over-fining.
trials for each wine to be treated in the winery. This is generally done using small
volume lots from the wine to be treated. It is important to remember that small scale
or laboratory fining conditions may not mimic the actual behavior of agents on a
commercial scale due to difficulties in the speed or extent of mixing. However it is
possible to determine the relationship between small scale fining trial and commercial
scale fining. This need not be done every time a wine is fined. We have found
reasonable reproducibility in scaling up from a fining trial once the "scaling" factors
are understood. It is also possible to adapt the small scale fining trial (adjust
rates of agent addition and mixing) to match that of the commercial operation.
Under typical winery conditions this has to be done empirically, by measuring loss
of haze forming potential with step wise addition of an agent and repeating the
step wise addition under a commercial scale and comparing the amount of
undesired component (tannin, protein) remaining in the treated wine. This procedure
can also be used to test for the potential of over-fining.
Over-fining is a term that has different meanings in different regions. Many
California winemakers consider over-fining to mean that there was a noticeable
and negative effect on wine quality. This is usually due to the removal of desired
flavor and aroma components. I prefer to call this particular problem "stripping" .
The French use over-fining to mean that the wine has become destabilized in
some way, that is, some of the added protein fining agent has not been removed
and will lead to subsequent colloid formation upon interaction with tannins. This
is especially problematic if the wine is exposed to tannins post fining, such as by
blending or barrel aging. Over-fining is particularly problematic in white wines fined
with gelatin. For the purposes of this class we will use the French definition
of over-fining. Over-fining should not be confused with failure of the fining
process or agent to remove existing components of the wine that will likewise
lead to haze formation later on in the aging of the wine. We will call this
phenomenon incomplete fining . It is important to note at this point that
rarely does any fining operation reduce the concentration of the undesired
component to the analytically undetectable range. The goal is to reduce the
concentration to a value below which it will not be noticeable as a problem.
California winemakers consider over-fining to mean that there was a noticeable
and negative effect on wine quality. This is usually due to the removal of desired
flavor and aroma components. I prefer to call this particular problem "stripping" .
The French use over-fining to mean that the wine has become destabilized in
some way, that is, some of the added protein fining agent has not been removed
and will lead to subsequent colloid formation upon interaction with tannins. This
is especially problematic if the wine is exposed to tannins post fining, such as by
blending or barrel aging. Over-fining is particularly problematic in white wines fined
with gelatin. For the purposes of this class we will use the French definition
of over-fining. Over-fining should not be confused with failure of the fining
process or agent to remove existing components of the wine that will likewise
lead to haze formation later on in the aging of the wine. We will call this
phenomenon incomplete fining . It is important to note at this point that
rarely does any fining operation reduce the concentration of the undesired
component to the analytically undetectable range. The goal is to reduce the
concentration to a value below which it will not be noticeable as a problem.
| Problems Associated With Fining: | ||
| • Lack of specificity | ||
| • Over-fining | ||
| • Oxygen exposure | ||
| • Loss of wine volume to fining lees | ||
| • Expense and need for clarification | ||
| • Additions of flavors/aromas if process is not neutral | ||
| • Potential addition of microbes | ||
Two other consequences of fining also need to be mentioned. Fining agents are
not sterile. Many are actually quite good carbon, nitrogen and energy
sources for microbes. If the winery is experiencing problems with spoilage, the
fining agents should not be ignored as a potential source of contaminants.
This is usually not a problem unless the fining agent has not been stored properly
(allowed to become wet, stored near other contaminated or possibly contaminated
materials, splashed with wine during the fining operation then put back in storage, etc.).
Some agents that are used in fining discussed below such as egg whites or spoiled
milk can add flavor or aroma "nuances" to the wine. In this respect, many consider
the wine to be "over-fined" if the fining agent can be detected sensorially in
the wine. This is in the same spirit of the French meaning of over-fining, just a
different type of problem caused by residual fining agent material remaining in the wine.
not sterile. Many are actually quite good carbon, nitrogen and energy
sources for microbes. If the winery is experiencing problems with spoilage, the
fining agents should not be ignored as a potential source of contaminants.
This is usually not a problem unless the fining agent has not been stored properly
(allowed to become wet, stored near other contaminated or possibly contaminated
materials, splashed with wine during the fining operation then put back in storage, etc.).
Some agents that are used in fining discussed below such as egg whites or spoiled
milk can add flavor or aroma "nuances" to the wine. In this respect, many consider
the wine to be "over-fined" if the fining agent can be detected sensorially in
the wine. This is in the same spirit of the French meaning of over-fining, just a
different type of problem caused by residual fining agent material remaining in the wine.
V. The Fining Agents
There are several different classes of fining agents used in wine production.
| Wine Fining Agents: | ||
| • Proteins | ||
| • Earths | ||
| • Colloids | ||
| • Synthetic Polymers | ||
| • Silica Suspensions | ||
| • Activated Carbon | ||
The most common agents are the proteins. There are four protein fining agents that
are used.
are used.
| Fining Agents: The Proteins | ||
| • Casein | ||
| • Gelatin | ||
| • Albumin | ||
| • Isinglass | ||
| The Protein Fining Agents: Casein | ||
| • Mixture of milk proteins | ||
| • Proteins have hydrophilic regions and areas of high negative charge due to extensive phosphorylation | ||
| • Insoluble in wine | ||
| • Can remove phenolics via hydrophobic interactions | ||
| • Can remove proteins via charge and hydrophobic interactions | ||
Casein is derived from milk and actually represents different protein species. These proteins
are of low molecular weight (less than 30 Kd) and are not soluble at low pH. The
casein proteins have regions of net negative charge due to the fact that they are
phosphorylated. These regions can undergo charge interactions with positively
charged species in the wine. The proteins also have hydrophobic or nonpolar
regions that are exposed when the caseins denature at wine pH. These regions can
interact with phenolic compounds and other components. Finally, most proteins will
have a net positive charge at wine pH due to the pKa values of the amino acid side
chains. Thus casein has areas of both positive and negative charge density on the
protein surface as well as nonpolar regions. Casein is generally used to remove
phenolic compounds and off-colors or bitterness. Casein use is quite problematic
however. Since the protein rapidly denatures at wine pH it will flocculate rapidly and
with itself (due to the possession of areas of net positive and net negative charge).
If this occurs then it can lead to incomplete fining. It is not soluble in water so
must be used in a slightly alkaline solution (with ammonium hydroxide) so it is
important to do this in a manner not impacting the pH of the wine.
are of low molecular weight (less than 30 Kd) and are not soluble at low pH. The
casein proteins have regions of net negative charge due to the fact that they are
phosphorylated. These regions can undergo charge interactions with positively
charged species in the wine. The proteins also have hydrophobic or nonpolar
regions that are exposed when the caseins denature at wine pH. These regions can
interact with phenolic compounds and other components. Finally, most proteins will
have a net positive charge at wine pH due to the pKa values of the amino acid side
chains. Thus casein has areas of both positive and negative charge density on the
protein surface as well as nonpolar regions. Casein is generally used to remove
phenolic compounds and off-colors or bitterness. Casein use is quite problematic
however. Since the protein rapidly denatures at wine pH it will flocculate rapidly and
with itself (due to the possession of areas of net positive and net negative charge).
If this occurs then it can lead to incomplete fining. It is not soluble in water so
must be used in a slightly alkaline solution (with ammonium hydroxide) so it is
important to do this in a manner not impacting the pH of the wine.
| Casein: The Problems: | ||
| • Tends to clump requiring good mixing | ||
| • Tendency to strip wine | ||
| • May impart characters to wine | ||
Casein does not lead to over-fining in the classic French definition, but can strip
wine of aroma and flavor. It can also be detected depending upon how the
casein was prepared and how pure the preparation is. Casein is generally
produced from coagulated skim milk typically made from commercially unacceptable
(that is, spoiled) milk.
wine of aroma and flavor. It can also be detected depending upon how the
casein was prepared and how pure the preparation is. Casein is generally
produced from coagulated skim milk typically made from commercially unacceptable
(that is, spoiled) milk.
| The Protein Fining Agents: Gelatin | ||
| • Animal by-product | ||
| • Net positive charge at wine pH | ||
| • Somewhat soluble in wine | ||
| • More neutral than other proteins | ||
| • Not as effective as other proteins | ||
Gelatin is derived from animal collagen (skin or bones). Gelatins are classified as
heat soluble, cold soluble and liquid, based upon molecular weight of the
principle species present and charge. The gelatins are produced in various
ways (chemical hydrolysis or enzymatic degradation) and have many uses
in food industries. Gelatins have a high content of glutamic acid and will
therefore be slightly positively charged or neutral at wine pH. The pKa of the
gamma-carboxyl group of glutamic acid is 4.25. It also contains a high
percentage of nonpolar amino acids, glycine, proline and hydroxyproline. The
more highly charged the gelatin the more active it is in removal of tannins
from wine. Gelatin can be dissolved in hot water and is frequently used in
conjunction with silica sols. The purpose of the silica gel is to prevent
over-fining with gelatin (high residual levels of gelatin).
heat soluble, cold soluble and liquid, based upon molecular weight of the
principle species present and charge. The gelatins are produced in various
ways (chemical hydrolysis or enzymatic degradation) and have many uses
in food industries. Gelatins have a high content of glutamic acid and will
therefore be slightly positively charged or neutral at wine pH. The pKa of the
gamma-carboxyl group of glutamic acid is 4.25. It also contains a high
percentage of nonpolar amino acids, glycine, proline and hydroxyproline. The
more highly charged the gelatin the more active it is in removal of tannins
from wine. Gelatin can be dissolved in hot water and is frequently used in
conjunction with silica sols. The purpose of the silica gel is to prevent
over-fining with gelatin (high residual levels of gelatin).
Gelatin: The Problem: Over-fining: requires use of an additional fining agent
to get rid of it
to get rid of it
| The Protein Fining Agents: Albumin: | ||
| • From egg whites | ||
| • Net positive charge at wine pH | ||
| • Removes bitter phenolics | ||
| • Softens astringency | ||
Albumin is produced from egg whites. In powder form it is obtained from the drying of egg
whites. It is comprised largely of two protein species, ovalbumin and conalbumin. Fresh
egg whites can also be used, but these will have a different composition than the dried
product. One to as many as eight egg whites may be used per barrel. Most experienced
tasters can detect egg whites at two to three per barrel, depending upon the wine, however.
Egg white protein can be dissolved in water, but excessive mixing should be avoided
as this will lead to significant foaming. Better solubility is obtained if a little potassium or
sodium chloride is added to the water. The albumin proteins also have a net positive
charge at wine pH and can remove phenolic compounds. Egg white fining is often
mentioned as the method of choice for the production of high end red wines. The only
problem with egg white fining is as noted above, if overdone, expert tasters will be
able to detect it, and this may be considered a fault or defect of the wine. The egg
white character is similar to the aroma of meringue
whites. It is comprised largely of two protein species, ovalbumin and conalbumin. Fresh
egg whites can also be used, but these will have a different composition than the dried
product. One to as many as eight egg whites may be used per barrel. Most experienced
tasters can detect egg whites at two to three per barrel, depending upon the wine, however.
Egg white protein can be dissolved in water, but excessive mixing should be avoided
as this will lead to significant foaming. Better solubility is obtained if a little potassium or
sodium chloride is added to the water. The albumin proteins also have a net positive
charge at wine pH and can remove phenolic compounds. Egg white fining is often
mentioned as the method of choice for the production of high end red wines. The only
problem with egg white fining is as noted above, if overdone, expert tasters will be
able to detect it, and this may be considered a fault or defect of the wine. The egg
white character is similar to the aroma of meringue
| Albumin: The Problems | ||
| • Not neutral, especially if egg whites rather than pure albumin is used | ||
| • Experienced tasters can tell if a wine has been fined with egg whites | ||
| The Protein Fining Agents: Isinglass | ||
| • From fish air bladders | ||
| • Net positive charge at wine pH | ||
| • Large surface area | ||
| • Forms stable, tight lees | ||
| • Least tendency to over-fine | ||
| • Neutral, does not add nuances | ||
Isinglass is a protein produced from the air bladder of fish. Like the other proteins, it
has a net positive charge at wine pH. It also tends to denature into "sheets" or
strands and thus has a large surface area for adsorption. It has the least tendency
to over-fine, and forms more stable (tight) lees than the other agents. It is also
neutral, not adding any nuances to the wine. There are two main problems with
isinglass, expense and availability. It is commonly produced from sturgeons
so its availability depends upon the availability of the fish. Some other types of
isinglass (or fish protein products) are available, but these tend to have lighter
lees and offer no advantages over other protein fining agents.
has a net positive charge at wine pH. It also tends to denature into "sheets" or
strands and thus has a large surface area for adsorption. It has the least tendency
to over-fine, and forms more stable (tight) lees than the other agents. It is also
neutral, not adding any nuances to the wine. There are two main problems with
isinglass, expense and availability. It is commonly produced from sturgeons
so its availability depends upon the availability of the fish. Some other types of
isinglass (or fish protein products) are available, but these tend to have lighter
lees and offer no advantages over other protein fining agents.
| Isinglass: The Problems | ||
| • Expense | ||
| • Availability | ||
Which protein fining agent is used should be decided after a fining trial. With respect
to removal of phenolic compounds, they are equivalent so the decision should be
based on other considerations. Some winemakers feel particular proteins are
easier to use or better in terms of diminished stripping or over-fining problems,
but this will differ on a case by case (wine by wine) basis. There is intense
research interest aimed at identifying plant proteins that may substitute for animal
proteins as wine fining agent. This is being fueled by concern over contamination
of animal based products with the agent causing mad cow disease in the European
community. The removal of soluble components such as protein by the protein
fining agents is facilitated by the presence of tannin. Tannins can be added to
wine in conjunction (the day before) protein fining agents. This practice is commonly
used in France to increase the efficacy of the protein agents and to guard against
over-fining. Tannin fining has other effects as well. Tannins can function as oxidation
targets reducing oxidative loss of wine components. Tannins may form complexes
with negative characters, and enhance removal of oxidative enzymes. Because
tannin dramatically impacts wine structure, additions should be made several weeks
prior to bottling.
to removal of phenolic compounds, they are equivalent so the decision should be
based on other considerations. Some winemakers feel particular proteins are
easier to use or better in terms of diminished stripping or over-fining problems,
but this will differ on a case by case (wine by wine) basis. There is intense
research interest aimed at identifying plant proteins that may substitute for animal
proteins as wine fining agent. This is being fueled by concern over contamination
of animal based products with the agent causing mad cow disease in the European
community. The removal of soluble components such as protein by the protein
fining agents is facilitated by the presence of tannin. Tannins can be added to
wine in conjunction (the day before) protein fining agents. This practice is commonly
used in France to increase the efficacy of the protein agents and to guard against
over-fining. Tannin fining has other effects as well. Tannins can function as oxidation
targets reducing oxidative loss of wine components. Tannins may form complexes
with negative characters, and enhance removal of oxidative enzymes. Because
tannin dramatically impacts wine structure, additions should be made several weeks
prior to bottling.
Fining Agents: The Earths
Naturally occurring clays or earths can also be used to absorb materials from wine
in the process of fining. The most common fining agent in this category
is bentonite. Bentonite is a natural montmorillonite clay.
in the process of fining. The most common fining agent in this category
is bentonite. Bentonite is a natural montmorillonite clay.
The Earths: Bentonite
It is an aluminum silicate that also contains magnesium, calcium and sodium.
Bentonite composition differs depending upon the source of the clay, and may
contain higher calcium or higher sodium.
Bentonite composition differs depending upon the source of the clay, and may
contain higher calcium or higher sodium.
| Bentonite | ||
| • Silicate (SiO2) | ||
| • Large surface area: occurs in sheets | ||
| • Net negative charge at wine pH: ideal for interaction with wine proteins | ||
| • Different forms occur differing in salts associated with silicate: Na+, K+, Ca2+ | ||
Bentonite dissociates into large sheets and has a net negative charge at wine pH.
It will exchange the calcium, magnesium and sodium ions for positively charged proteins in wine.
It will exchange the calcium, magnesium and sodium ions for positively charged proteins in wine.
| Bentonite | ||
 | Functions by exchange of associated cation for wine components having a higher affinity | |
The cation exchange mechanism means that the displaced cation will be in the wine.
Bentonite is not specific, and will bind many wine components.
Bentonite is not specific, and will bind many wine components.
| Bentonite Levels: | ||
| • Typically 1-4 lbs/1000gal (0.12-0.48 g/L) is ample to remove wine protein. If >10 lbs/1000 gal (>1.0 g/L) is needed, haze problem might not be due to protein. | ||
Because of its affinity for protein, it is not surprising that bentonite is most commonly
used to
achieve protein stability in wines. It is typically used in the range of 1 to 4 lbs/1000 gal
or 12 to 48 g/hL. If significantly higher concentrations are needed, then the haze is
likely not proteinaceous in origin or the proteins involved are not highly charged at
wine pH. This is rare, but we have seen it happen in white wines made from
juices that have undergone a high temperature short time treatment to eliminate
laccase. Bentonite is less effective in the removal of proteins protected by
polysaccharide components. The heat treatments may lead to the appearance
of protective polysaccharides that prevents full agglutination of the proteins
present. It is our experience that these types of colloids are very difficult to
remove from the wine, but will eventually agglutinate during aging so will be a problem
if the wine is bottled.
used to
achieve protein stability in wines. It is typically used in the range of 1 to 4 lbs/1000 gal
or 12 to 48 g/hL. If significantly higher concentrations are needed, then the haze is
likely not proteinaceous in origin or the proteins involved are not highly charged at
wine pH. This is rare, but we have seen it happen in white wines made from
juices that have undergone a high temperature short time treatment to eliminate
laccase. Bentonite is less effective in the removal of proteins protected by
polysaccharide components. The heat treatments may lead to the appearance
of protective polysaccharides that prevents full agglutination of the proteins
present. It is our experience that these types of colloids are very difficult to
remove from the wine, but will eventually agglutinate during aging so will be a problem
if the wine is bottled.
| Bentonite: The Problems | ||
| • Must swell properly in water or water/wine mixture before use | ||
| • High lees volume | ||
| • Addition of ions that may encourage tartrate instability | ||
Bentonite can be challenging to swell properly. It will form cement especially with
insufficient mixing. It is typically prepared as a 5 to 15% slurry. Swelling is
faster at higher temperatures. Some winemakers prefer to swell the bentonite in
wine, but it will coagulate much faster and loses some adsorptive capacity. Other
winemakers feel that the bentonite is more effective at removal of protein if
juice rather than wine is treated, but this appears to be juice-specific and not
a general finding. It may be necessary following bentonite fining to add a
protein such as casein to fully strip the bentonite from the wine. Bentonite
fined wine can typically be clarified by racking, but in some cases filtration
might be necessary. Since bentonite adds cations to the wine, it is wise to tartrate
stabilize post bentonite treatment. Bentonite has a tendency toward a high lees
volume, perhaps as high as 20% of the volume of the wine treated depending
upon the conditions used. Some winemakers recommend that bentonite treatment
be performed in shallow versus deep tanks. This provides an initial larger surface
area of bentonite to wine which can improve adsorption.
insufficient mixing. It is typically prepared as a 5 to 15% slurry. Swelling is
faster at higher temperatures. Some winemakers prefer to swell the bentonite in
wine, but it will coagulate much faster and loses some adsorptive capacity. Other
winemakers feel that the bentonite is more effective at removal of protein if
juice rather than wine is treated, but this appears to be juice-specific and not
a general finding. It may be necessary following bentonite fining to add a
protein such as casein to fully strip the bentonite from the wine. Bentonite
fined wine can typically be clarified by racking, but in some cases filtration
might be necessary. Since bentonite adds cations to the wine, it is wise to tartrate
stabilize post bentonite treatment. Bentonite has a tendency toward a high lees
volume, perhaps as high as 20% of the volume of the wine treated depending
upon the conditions used. Some winemakers recommend that bentonite treatment
be performed in shallow versus deep tanks. This provides an initial larger surface
area of bentonite to wine which can improve adsorption.
Fining Agents: The Colloids
Colloidal materials can also be used as fining agents. Polysaccharide material can
be used in a fining treatment. The polysaccharides generally derive from agar or gum Arabic.
be used in a fining treatment. The polysaccharides generally derive from agar or gum Arabic.
| Colloidal Fining Agents: | ||
| • Natural polysaccharides | ||
| • Agar | ||
| • Gum Arabic | ||
| • Sparkalloid: alginate based | ||
| • Ferrocyanide colloidal preparations | ||
| • Naturally dispersed or "protective" colloids can hold proteins, tartaric acid crystals, other colloidal materials in suspension | ||
| • Colloidal fining agents neutralize surface charges on naturally dispersed colloids thereby allowing them to dissolve or coagulate | ||
In the United States , one proprietary colloidal preparation is known as Sparkalloid.
Colloidal fining agents can neutralize surface charges on other naturally dispersed
colloids causing agglutination or dissolution of the existing particles. They aid in the
removal of more finely suspended particles. It is important to know the mechanism
of action or stability of a colloidal preparation in wine, as some effects may be temporary.
We also include ferrocyanide preparations in the section on colloids. These preparations
are used to remove transition metal cations such as residual copper from copper fining.
In some countries non-colloidal forms of ferrocyanide are permitted, but only colloidal
forms are allowed in the United States . Wines treated with ferrocyanide must be
assayed for residue levels. Use of colloidal ferrocyanide preparations is prohibited
in many countries. It is generally thought that it is best to adjust winemaking operations
so that ferrocyanide treatment is unnecessary. It is rarely used in the United States .
Use is so rare that commercial preparations are no longer routinely available.
Colloidal fining agents can neutralize surface charges on other naturally dispersed
colloids causing agglutination or dissolution of the existing particles. They aid in the
removal of more finely suspended particles. It is important to know the mechanism
of action or stability of a colloidal preparation in wine, as some effects may be temporary.
We also include ferrocyanide preparations in the section on colloids. These preparations
are used to remove transition metal cations such as residual copper from copper fining.
In some countries non-colloidal forms of ferrocyanide are permitted, but only colloidal
forms are allowed in the United States . Wines treated with ferrocyanide must be
assayed for residue levels. Use of colloidal ferrocyanide preparations is prohibited
in many countries. It is generally thought that it is best to adjust winemaking operations
so that ferrocyanide treatment is unnecessary. It is rarely used in the United States .
Use is so rare that commercial preparations are no longer routinely available.
Fining Agents: Synthetic Polymers
Wines may also be treated with synthetic polymers. These agents are used to
remove specific phenolic components. The principle synthetic polymers
used are polyglycine, polyamide and polyvinylpolypyrrolidone (PVPP). The carbonyl
oxygen atoms on the surface of these polymers act as adsorption sites for phenolic
compounds.
remove specific phenolic components. The principle synthetic polymers
used are polyglycine, polyamide and polyvinylpolypyrrolidone (PVPP). The carbonyl
oxygen atoms on the surface of these polymers act as adsorption sites for phenolic
compounds.
| Synthetic Polymers: | ||
| • Polyglycine | ||
| • Polyamide | ||
| • Polyvinylpolypyrrolidone (PVPP) | ||
| • All have carbonyl oxygen atoms on surface that act as adsorption sites | ||
These agents remove subsets of phenolic compounds and are particularly effective at
removal of monomeric phenolics that will oxidize to off-colors.
removal of monomeric phenolics that will oxidize to off-colors.
Fining Agents: Silica Suspensions
Silica suspensions (sols or gels) were mentioned previously as being a useful adjuvant
to gelatin fining. The silica sols are principally used to accelerate fining processes
as well as to remove excess fining agent. This can improve filterability of the wine.
to gelatin fining. The silica sols are principally used to accelerate fining processes
as well as to remove excess fining agent. This can improve filterability of the wine.
| Silica Suspensions: | ||
| • The "sols" | ||
| • Used primarily with gelatin | ||
Fining Agents: Activated Carbon
Activated carbon can also be used to remove unwanted components from wine.
Carbon is very effective at stripping wine so should be used only as a last resort.
Carbon is very effective at stripping wine so should be used only as a last resort.
Activated carbon is not very selective and will remove a wide range of compounds.
It is the method of choice for highly tainted wines.
It is the method of choice for highly tainted wines.
| Activated Carbon: | ||
| • High and broad affinity | ||
| • Removes color, wide range of phenolics | ||
| • Strips wine: used only as a last resort to salvage a wine for blending | ||
If activated carbon is used, then the wine is frequently not of the quality needed
for production of a varietal wine. It can be used in blends. In contrast to filtration,
fining can impact the flavor and aroma profile of a wine. Production levels used are
typically low enough to have little to no impact, but it is possible to strip a wine if
the winemaker is not judicious in the use of these agents.
for production of a varietal wine. It can be used in blends. In contrast to filtration,
fining can impact the flavor and aroma profile of a wine. Production levels used are
typically low enough to have little to no impact, but it is possible to strip a wine if
the winemaker is not judicious in the use of these agents.
In contrast to filtration, fining can have an impact on the flavor and aroma of wine.
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