Monday, June 13, 2011

Wine and Wine Fining

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
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.
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 
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).

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.
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.
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.
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.
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.
Chemical Instabilities: Oxidation Products
•  Off-color
•  Off-characters
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".

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.
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.
•  "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.
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.

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.
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.
Goal of Fining:
Removal of soluble components that are undesired stylistically or that will
 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.
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.
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.
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.
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.
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.
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.
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.

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.
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.
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.

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.
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.
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.
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).
Gelatin: The Problem: Over-fining: requires use of an additional fining agent
 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
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.
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.
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.
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.
•  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.
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 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.
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.
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.
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.
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 
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.
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.
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.
Activated carbon is not very selective and will remove a wide range of compounds. 
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.
In contrast to filtration, fining can have an impact on the flavor and aroma of wine.

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