​Crystalline Salt Stabilization [1]

• Potassium Bitartrate (Tartrate) Stabilization
  
• Calcium Tartrate Instabilities
  
• Other Crystalline Deposits

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 Potassium Bitartrate (Tartrate) Stabilization
Sometimes referred to as “wine diamonds”, cream of tartar, or KHT, these crystals are caused by tartaric acid binding with potassium to create potassium bitartrate, which crystallizes when chilled. They are undesirable because the consumer may interpret them as a problem with the wine.

Stabilization Processes
Sufficient time before bottling can allow crystals to naturally participate, however this can take a long time. To accelerate this process, other participation techniques are used.
Chilling or cold stabilization in temperature controlled tanks enhances crystallization prior to bottling. In this process:

• Wine is chilled to near its freezing point with higher ABV lowering the freezing point. Example freezing points: 10% ABV: ~25 °F, 12% ABV: ~23 °F, 14% ABV= ~21 °F.1
• The crystals are removed via filtration or centrifugation before the wine is allowed to warm to ambient temperature.

Membrane Filtration
Reverse osmosis is used to remove water, which increases bitartrate concentration and promotes crystal formation (Jackson, Wine Science). After the crystals are removed, the water is added back.

Electrodialysis
Two electrically charged membranes prevent the passage of ions of the opposite charge. For tartrate stability, one membrane is permeable to tartrates, and the other to potassium and calcium ions, and when the salts cross the membranes they are removed by a conductive solution, which is discarded.2 Drawbacks include lowering of the wine’s pH, and the potential removal of sulfur dioxide and other desirable compounds (Jackson, Wine Science).

Ion Exchange
Wine is passed through a column where sodium-containing resin exchanges the sodium for potassium. Sodium bitartrate is more soluble than the potassium salt, so it is much less likely to precipitate. However, ion exchanges are prohibited in certain jurisdictions, and can increase the sodium content of the wine.

Additives Which Restrict
Crystal Formation
For wines to be consumed immediately after purchase, some compounds can be used to restrict crystal formation in a limited manner. These techniques are used in the absence of the equipment to adequately chill the wine, and include:

• Direct seeding with potassium bitartrate crystals or filters embedded with seed crystals. These stimulate crystal growth and allow for the crystals to be filtered or centrifuged out (Jackson, Wine Science).
• Metatartaric acid, a mixture of polymers with different molecular weights formed by esterification of tartaric acid (Marchal and Jeandet 2009), is used to temporarily prevent crystal formation. The Australian Wine Research Institute (AWRI) notes that metatartaric acid slowly hydrolyzes back into tartaric acid, making the eect last for more than two years at 10–12 °C, and 12-18 months at ~10 °C - 18 °C.
• Carboxymethyl cellulose (CMC) is a water-soluble, linear chain polysaccharide which does not cause changes in pH or titratable acidity, and does not generally have any sensory impact. Its drawbacks include: having a limited impact on stability, not being suitable for red wines, as it can impact color, the need for protein stabilization before its application, and the fact that no additions to the wine can occur after the addition of CMC (Jackson, Wine Science).
• Mannoproteins, complex polymers consisting largely of mannose (a type of sugar) and certain proteins, can inhibit KHT crystal growth without affecting a wine’s organoleptic properties. These are added after fining and pre-filtration in typical doses of 100-300 mg/L. However, mannoproteins can react with other wine components over time and lose effectiveness.

Calcium Tartrate Instabilities1
The crystallization of calcium L-tartrate, known simply as calcium tartrate, is commonly caused by an excess of calcium carbonate from deacidification, the use of cement cooperage, or the use of casein or other milk products for fining. Higher pH values can cause greater instability, while some organic acids can help to enhance a wine’s calcium tartrate-holding capacity. Crystals often form in white wine. They can be less noticeable in red wine, and occur slowly and often after the wine is bottled, sometimes months later.

Stabilization process:
Temperature is not a major factor in calcium tartrate precipitation, and there is a lack of reliable cold stabilization procedures and tests to predict the instability. Beyond avoiding calcium instabilities in the first place, the few ways to stabilize the wine are primarily:

Seeding with calcium tartrate crystals, then clarification for their removal.

​Inhibitory compounds may slow or even prevent nucleation by binding with free calcium or tartrate and lowering the supersaturation.

• Malic acid may be added to sparkling wine (with the dosage) to prevent calcium tartrate crystallization after bottling.
• Polyuronic acids of grape pectins can also be added.

Ion exchange can reduce calcium content, and because of the process’ efficiency, typically only part of the wine is treated to minimize any flavor loss.
​

Other Crystalline Deposits [2]
Though uncommon, these include: Ellagic acid, calcium oxalate, favonols, calcium sulfate, and calcium mucate.

For an insightful literature review:
Lasanta, Cristina & Gomez Benitez, Juan. (2012). Tartrate stabilization of wines. Trends in Food Science & Technology. 28. 52–59. 10.1016/j.tifs.2012.06.005. Retrieved from:
www.researchgate.net/publication/257345999_Tartrate_stabilization_of_wines

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​Metal Instabilities

​Heavy metals that do not coprecipitate out with yeast cells during fermentation may form insoluble salts and hazes (casse). These have been significantly reduced by the mass adoption of stainless steel winery equipment.

• Ferric (Iron) Casse
• Copper Casse

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Ferric (Iron) Casse [1] 

Source: Ferric casse was more common when cast iron was used in equipment and piping. Now corroded stainless steel, improperly soldered joints, and fining and decoloring agents including bentonite are the primary sources of iron in wine. However, these sources typically do not contribute enough iron to cause a casse.

Haze color

• White (ferric phosphate) is the most common ferric casse. It is dependent on pH (occurs at pH of 2.9-3.6), redox potential, phosphate content (because iron in its ferric oxidation state is highly insoluble in the presence of phosphate, including that from diammonium phosphate), and the presence of certain wine acids.
• Blue (ferric tannate) casse which mainly occurs in red wine.

Mechanism: At ~6 mg/L iron, ferric ions form insoluble particles with anthocyanins and tannins, and are exposed to oxygen.

Stabilization Process

• Iron casse is primarily avoided by avoiding iron contamination.
• Less common processes include additions of calcium phytate, ferrocyanide (as it precipitates most metal ions including copper), lead, zinc, and magnesium (though its usage is prohibited in many countries). [2]

​Copper Casse [8], [9]
More often a problem in white wines, it can also cause haziness in rosé wines. Copper casse forms solely in the absence of oxygen, and develops only after bottling.

​Mechanism

• Concentrations above .05 mg/L are strongly susceptible to instability, which consists of a copper-protein complex.
• ​Light exposure speeds the reduction of copper.

Source

• Major contributors include copper-containing fungicides. The late addition of copper sulfate (CuSO4) is also a source, as not enough time is allowed for it to precipitate out.
• Soil and grape juice contact with unprotected brass or bronze winery fittings can provide minor copper contributions.

Stabilization process
Typically, reduction occurs naturally during fermentation when yeast binds to copper and forms sulfides that are removed with the lees. This is helped by proper yeast management. However, copper can be fined out, using:

• Polyvinylimidazole/polyvinylpyrrolidone (PVI/PVP) which has great metal binding capability and can remove metal ions including copper, iron, lead, cadmium and aluminum from both red and white wine (Mira et al. 2007).
• Bentonite can be used for small amounts of copper removal, with the addition of 0.1 g/L in either red or white, lowering the copper concentration by about 0.1 – 0.2 mg/L. However, it does not have the capacity to remove large amounts.

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Protein Instabilities [10]

• ​Mechanisms of Instability
• Stabilization Process: Fining

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Excessive quantities of proteins can coagulate with compounds like polysaccharides and polyphenols to form irreversible hazes, especially if the wine is warmed. Though unsightly and considered wine faults, they typically do not impact aroma, but can cause economic losses due to customer rejection.

Mechanisms:
The development of protein haze cannot be predicted by overall protein content, and is not homogeneous in formulation, but rather is caused by a multitude of factors which have challenged oenologists to find a way to predict their development.

Heat is a major influencing factor, and therefore dictates the amount of protein stabilization required. For this reason, wine of the same vintage purchased at the winery’s tasting room may taste different than wine purchased elsewhere, due to the need for heat protection.

​Polyphenols complex with and naturally precipitate out proteins. As white wine has low phenolic content, haze formation is more likely.

Proteins may also serve as nuclei around which soluble iron, copper, and other heavy metals may deposit.

Other susceptibility factors:

• Cultivar. Some grapes like Muscat, Gewürztraminer, Sauvignon Blanc and Semillon are particularly prone to haze development.
• Maturity, climate, molecular size, electrical charge, as well as interaction and precipitation with other components.
• Types of proteins that cause haze11:
  • Pathogenesis-related (PR) proteins of thaumatin-like proteins and chitinases are the most abundant classes of proteins in grape juice and white wine. They are positively charged at wine pH and tolerant of the low pH in juice and wine.
  • Β-glucanase-produced hazes are rare but possible.
• Some of the ways proteins complex:
  • Thermally-labile proteins are those that break down when exposed to heat.
  • The formation of insoluble protein-tannin complexes.
  • About half of the total wine protein is bound to grape phenols, which are responsible for protein haze formation.

Stabilization Process: Fining  [12]

Fining agents are used to physically or chemically bind to the wine’s components, including unstable proteins, thereby precipitating out the unwanted compounds. This can help reduce:

• A wine’s astringency and/or bitterness through the reduction of tannins and other polyphenols.
• Color, by the adsorption and precipitation of polymeric phenols and tannins.
• The potential for haze formation.
• Off-odors and undesired aromas.
• Some pesticide residues. Ruediger et al., 2004 found that fining with activated carbon could reduce the quantity of fungicides and insecticides in wine. However, the greatest reduction was to those that were the least soluble. These included chlorothalonil, chlorpyrifos and dicofol. [13] 

General Process:

• Bench trials, which are small-scale laboratory tests, should be conducted to evaluate what fining is needed, as the grape chemistry changes every vintage. This evaluation includes assessment of the fining agent for the presence of any taints or off-flavors. Insight into the in-depth testing process can be found at: www.awri.com.au/industry_support/winemaking_resources/sensory_assessment/screening_tests/
• Once tested, the fining agent is applied, often by mixing it with water to form a slurry. Direct addition is also possible for some fining agents.
• The fining agent is precipitated out by centrifugation, filtration or racking (settling).
• Heat stability is then tested to confirm fining’s effectiveness.

Mechanisms [14]

• Fining agents typically work by adsorption (adhesion to) the undesired molecules, especially proteins, to help precipitate them out of solution. Many have an electrical charge which helps to create ionic bonds that help adsorption.
• The adsorption properties can be impacted by the method of preparation, the quantity employed, pH, metal content, temperature, age of the wine, and previous treatments.

Drawbacks
Fining is imprecise as to what it removes, and can excessively remove compounds from wine.

• Albumin
• Casein
• ​Gelatin
• Isinglass
• Kieselsol
• PVVP

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Albumin (Egg White Proteins)
Process

• Dosage
  • Red wine dosage: 30 – 240 mg/L
  • White wine dosage: Not recommended
• Albumin fining is often carried out when the wine is in barrel or prior to bottling.
• Traditionally in Bordeaux, egg whites required the addition of sodium chloride (table salt) to solubilize the albumin.
• The type of egg white is chosen. This can be in dried and frozen form.
• Wine temperature at addition: ~10°C.
• In a beaker, the required number of egg whites (as a guide, 2-8 per 225L of wine) are combined with 10 times their weight in distilled water. This mixture is adjusted to pH 7. The egg white solution must be prepared fresh and added to the wine on the same day by slow and thorough mixing. A week is allowed for settling before the wine is racked or diatomaceous earth filtered. A small amount of foam might appear on the top of the wine, which can be skimmed off or gently stirred in.

Mechanisms
The protein binds with the larger polymeric material in the wine.

Benefits

• Color Removal: Medium
• Tannin Removal: High. It is also very good for fining tannic wines with some age because it tends not to remove protective colloids (Jackson, Wine Science).
• Clarity and Stability: Low
• Tendency to Overfine: Medium
• It is a simple technique
• Used to soften and improve the suppleness of the wine by removing phenolic compounds associated with harsh astringency in red wines.

 Challenges 
The development of masque: Albumin can interact with fatty acids and form a haze called masque on the inner surface of sparkling wine bottles (Jackson, Wine Science).

Casein (or Skim Milk)
Casein is the principal protein in milk.

Process

• Dosage:
  • White wine dosage: 50 – 250 mg/L
  • Red wine dosage: 50 – 250 mg/L
• The type of casein is chosen, with potassium caseinate being the most common. Other options include casein, potassium caseinate, mixtures of potassium caseinate with bentonite/silica, and skim milk.
• Wine temperature at addition: ~10 °C.
• Potassium caseinate, or casein, is weighed out and dissolved into a minimal volume of distilled water. The solution is slowly added into the wine and mixed immediately. A week is allowed for settling before racking or diatomaceous earth filtration.

Mechanism

• Casein, in association with sodium or potassium ions, forms a soluble caseinate that readily dissolves in wine. In wine, the salt dissociates and insoluble caseinate is released.
• Adsorbs and removes negatively charged particles as it settles.

Benefit

• Color Removal: Medium
  Primary used as a decolorant for white wine. Though not as effective in color removal, casein avoids the oxidative degradation often associated with carbon.
• Tannin Removal: Medium
• Used for fining white wine and sherries to reduce the level of phenolic compounds associated with bitterness and browning. It is softer than gelatin or isinglass.
• Clarity and Stability: Low
• Tendency to Overfine: Medium

Challenges
It can be a decolorant if used in red wine.

​Gelatin
A soluble albumin-like protein derived from the prolonged boiling of animal tissues (typically bones, skin, and tendons).

Process

• Dosage
  • White wine dosage: 15 – 120 mg/L
  • Red wine dosage: 30 – 240 mg/L
• The type of gelatin is chosen (powder or liquid), with the liquid form being more common. If powdered, the gelatin must be first diluted into a liquid.
• Wine temperature at addition: ~10 °C.
• The liquid form of gelatin is measured out before its direct addition to the wine. The gelatin is slowly and thoroughly mixed in. A few days are allowed for settling before the wine is racked or diatomaceous earth filtered.
• Gelatin can be added:
  • During the pressing process of white juice, to aid clarification and to reduce the level of phenolic compounds associated with bitterness, astringency and browning.
  • Early in the maturation process of red wine to avoid color losses that would be more pronounced if conducted later (due to the continuing polymerization of anthocyanins with tannins).
• Mechanism: Primarily interacts with larger polyphenolic compounds, and therefore has a more profound effect on older wines with a larger percentage of large polyphenols. It can also be added in conjunction with enological tannins to provide better clarification.

Benefits

• Color Removal: High
• Tannin Removal: High
• Gelatin is primarily used to remove excess tannins from wines:
• In red wine, it can reduce the level of phenolic compounds associated with excessive bitterness and astringency, and might also remove some color.
• In white wine, it can help remove the harshness and color of press juice prior to fermentation.
• Clarity and Stability: Low
• Gelatin is often added to white juice, particularly pressings, to aid clarification.
• Tendency to Overfine: High

Challenges

• Of the proteinaceous fining agents, gelatin is the most aggressive and can easily result in overfining and color removal.
• Excessive fining with gelatin can cause an undesirable color loss in red wines.
• Excessive usage can increase the risk of protein haze caused by residual proteins in the wine, as gelatin is wine soluble and heat unstable. This may be mitigated by the simultaneous addition of flavorless tannins, Kieselsol, or other protein-binding agents (Jackson, Wine Science).

Isinglass
Derived from proteins extracted from the air bladder of fish, notably sturgeons, it is essentially a preparation of collagen.
Process

• Dosage
  • Dosage in white wine 10-100 mg/L
  • Dosage in red wine: Not recommended.
• The type of isinglass is chosen and prepared if necessary
• ​Sheet isinglass needs to be rinsed to remove fishy odors.
• Flocculated isinglass. The flocculated form does not have to be rinsed to remove fishy odors.
• Wine temperature at addition: 10 °C.
• Isinglass is weighed out and dissolved into water to create a 0.5 % w/v solution.
• The solution is slowly and thoroughly mixed into the wine. A few days is allowed for settling, before the wine is racked or diatomaceous earth filtered.

Mechanisms: Reacts with monomers and smaller polyphenolic compounds.

Benefits

• Color Removal: Low
• Tannin Removal: Medium
• Clarity and Stability: Medium
• Primarily used to clarify white wine so it becomes brilliantly clear and the yellow color intensifies.
• Tendency to Overfine: Low
• It has a less dramatic effect on the astringency and body of the wine compared to gelatin.
• Can help enhance a white wine’s flavor by:
  • Helping remove harsh tates from its reaction with monomers and smaller polyphenolic compounds.
  • Bringing out or unmasking fruit characters without causing large changes in phenolic levels. It is less active towards condensed tannins than either gelatin or casein.
  • Has a less profound effect on the condensed phenolics principally responsible for astringency and body, compared to other protein fining agents.
  • Does not require extensive counter-fining as compared with other proteinaceous fining agents.

Challenges

• Settles slowly.
• Produces a voluminous sediment that tends to plug filters.
• Can impart a fishy odor to the wine, and thus should always be preceded with an assessment of a laboratory fining trial.
• An abundance of caution not to disturb the lees when racking or filtering is required, as isinglass’ precipitate is typically light and fluffy, making it susceptible to agitation back into the wine.
• Excessive use of isinglass can cause residual proteins in the wine, which may increase the chance of a protein haze formation.

Kieselsol [19]
An aqueous suspension of silicon dioxide (silica gel).
Process (for Gelocolle, available from Scott Labs)

Dosage: 200-1000 mL/hL
Should be thoroughly mixed directly into the wine one hour after fining with organic fining agents.

​Mechanisms: Available in both positively and negatively-charged forms, which allow it to adsorb and remove the oppositely-charged colloidal material.

Benefits
Helps compact lees and reduces the risk of overfining. It is also useful for difficult-to-filter wines, where it helps chelate proteins and other compounds.

Other Fining Agents

• Oenological tannins can be used to precipitate out proteins before bottling so that they can be removed with bentonite. They also have other uses, depending on their source and production methodology.
• Chitosan, a polysaccharide derived from the shells of crustaceans, has a positive ionic charge and is used to remove excess color and phenols from white wines. However, it can be an allergen if proper procedures are not followed.
• Carrageenan, a protein derived from red seaweed, may be more selective than bentonite in removing wine proteins without also removing desirable wine sensory compounds.20

For more potential fining agents, read:
www.wineaustralia.com/news/articles/is-it-good-night-for-bentonite

Polyvinylpolypyrrolidone (PVPP)
A synthetic polymer that acts similarly to proteinaceous fining agents.

​Process

• Dosage
  • White wine dosage: 100 – 800 mg/L
  • Red wine dosage: 100 – 450 mg/L (though not commonly used)

PVPP is weighed out. A slurry of a minimal volume of distilled water is mixed into the wine. A few days are required for settling, before filtration with diatomaceous earth or pad filter.
For color reduction in white wine, combining PVPP with carbon is often more effective, as it helps clarify the carbon particles.

Mechanisms
PVPP is practically insoluble in wine and absorbs the low molecular weight phenolics, especially anthocyanins and catechins.

Benefits

• Reduces bitterness. In particular, certain flavans and mono- and dimeric phenolics are removed (Jackson, Wine Science). For this, it is usually added relatively early in maturation.
• Gentles and helps to preserve wine aroma, unlike some other fining agents.
• Color removal:
  • In white wine: Effective in the prevention of pinking, oxidative browning, and the removal of brown phenolic by-product.
  • In red wine: Can help brighten color.
• Removal of off-flavors.
• Reduces the level of phenolic compounds associated with astringency in white wine.

Drawbacks
At high rates, it can result in color and flavor stripping.

Common Fining Agents

Fining agents are typically grouped by their chemical/physiological type: 
​Earth (materials), protein, polysaccharides, carbon, synthetic polymers, silicone dioxide

• Bentonite
• Other Earth Materials
• Carbon
• Gum Arabic

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Bentonite
(A Fine Clay of Aluminum Silicate)
Bentonite is a clay uniquely formed from volcanic ash.
Process

• Dosage
  • White wine dosage: 200 – 1000 mg/L
  • Red wine dosage: 200 – 500 mg/L

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Types of bentonite
Bentonite varies by primary composition, source, and level of purity, particle size, adsorption capacity, and swelling ability, is chosen.
​
Sodium bentonite:

• Usage: More common
• Physical Structure: Looser lattice structure and high dispersion rate.
• Benefits: Has a higher surface area than calcium.
• Drawbacks: Sediment can be more difficult to remove (racking is more difficult).
  
  

Calcium bentonite

• Usage: Less common, but can be a good riddling aid in méthode champenoise (Zoecklein, 1988).
• Physical Structure: Tighter lattice structure due to a charge density two times that of sodium bentonite (McBride, 2020).
• Benefits
  • Produces a denser sediment that is easier to remove.
  • Does not liberate sodium into the wine.
  • Drawbacks
  • Tendency to clump.
  • Provides less surface area for fining.
  • Extraction of calcium into wine is possible.
  • Does not precipitate out as much as sodium bentonite.
  • Commercially available combinations of sodium bentonite and calcium bentonite are common. There are also formulations designed for additions during fermentation or during cross-flow filtration.

Process
Bentonite is first weighed out, then slowly stirred into an adequate volume of 60 °C water to create a 5% w/v solution, unless otherwise specified by the manufacturer. The suspension is left to stand overnight, then thoroughly mixed to avoid clumps before addition into the wine. Zoecklein (1988) noted that, as three-quarters of the peptides and proteins react to bentonite within the first minute of contact, removal of the bentonite can be 'in line' with the proper filtration or centrifugation equipment to prevent the leaching or 'sloughing off' of proteins from the bentonite platelets.
​
Bentonite may be counterfined (precipitated out with another fining agent). According to Zoecklein (1988):

• Kieselsol (aqueous silicon dioxide) aids in lees compaction.
• Gelatin, a positively charged protein, can also aid in lees compaction.
• Tannins and casein can help accelerate settling of bentonite (Jackson, Wine Science).

Timing of Bentonite Addition

• Added to juice: As grape juice contains many proteins that will naturally precipitate out during fermentation, much higher rates of bentonite are often required. Bentonite additions to the fermentation vessel can be beneficial for tank-fermented whites and rosés that need protein stabilization. This can help preserve aromatics, minimize racking steps, and save time when compared to post-fermentation bentonite additions.16 For more on the topic, read this guide by Scott Labs: https://scottlab.com/how-to-ferment-wine-on-bentonite-fermobent
• Towards the end of fermentation: Aids in yeast settling and reduces the number of racking/clarification steps.
• Performed after blending or sweetening (and fermentation): Most typical scenario, especially for white wine. This is desirable because a rise in the pH of the blended product can reduce protein solubility and increase the potential for subsequent haze formation.
• The effectiveness of bentonite partially depends on the wine’s pH.

Mechanisms
(from Zoecklein, 1988)
Bentonite, when hydrated, exists as small negatively-charged colloidal plates of 1 nanometer (NM) by 500 NM, with enormous surface area and positively charged platelet edges. This makes it act like a multiplated, linear, long-chain, negatively charged molecule that adsorbs positively charged proteins, which can also bind to a small amount of negatively charged proteins.

General Benefits

• Principally used to remove proteins, including heat-unstable proteins, from white wine and juice (AWRI).
• ​Usage with some red wines may enhance membrane filterability, due to a reduction of the colloidal particles in suspension (Zoecklein, 1988). However, red wine fining should be limited, as it can reduce color by the adsorption of anthocyanins (AWRI).
• Limits the development of copper casse.
• It can correct for the addition of excessive amounts of proteinaceous fining agents by inducing their precipitation (Jackson, Wine Science).
• Settles out relatively quickly and is easily filtered, making it one of the few fining agents that does not create a stability or clarification problem.

Drawbacks

• May create aroma loss in wine, especially in wines with higher protein varietals (McBride, Scott Labs).
• A tendency to produce voluminous sediment (which can cause considerable wine loss during racking), but this loss can be recovered via centrifugation or filtration.
• Can affect red wine color by binding with positively-charged anthocyanins, causing up to 15% color removal. The amount of color removal is dependent upon the temperature and age of the wine. It removes more color from younger wines than gelatin, for example, while the opposite is true for older wines.
• Can cause excessive lees and flavor stripping. This can be mitigated by fermentation in contact with bentonite, an age-old practice used in Europe for protein stabilization, which also avoids or minimizes the need for subsequent bentonite addition into wine (Zoecklein, 1988).
• Deactivates enzymes.
• Can leach metals like aluminum, calcium, iron, arsenic, and lead into the wine. These levels are governmentally regulated for, and tested for.

For more insight into bentonite fining:

• Zoecklein, B. (1998). Bentonite Fining of Juice and Wine. Retrieved May 19, 2022, from www.apps.fst.vt.edu/extension/enology/downloads/bentonite01.pdf
• Scott Labs. (2020, July 24). Playing with dirt: Specialized bentonites for protein stability. YouTube. Retrieved May 19, 2022, from https://www.youtube.com/watch?v=5NJmQ1WPzXo

Copper Sulfate (or Occasionally Silver Salts) [20]
Copper sulfate (CuSO4) is commonly used to prevent sulfur off-odors from red and white wines. This is especially important for screw-cap wines that are not permeable to oxygen.

Process

• Dosage: Up to 0.5 mg/liter of copper sulfate. Residual levels of copper should not exceed 0.2 mg/liter (the usual legal limit).
• Added at least one month before bottling. Resulting copper complexes should precipitate, then be eliminated by racking or filtration.

Mechanisms:
Copper sulfate reacts with sulfhydryls like H2S, MeSH and EtSH to form copper salts, which were previously thought to be insoluble and easy to remove via filtration. However, copper sulfide does not precipitate out after reacting as was once thought. A large proportion may remain in the wine post-filtration.

​Benefits
Prevents the need for aeration to remove ‘reductive faults,’ as wines containing sulfhydryls (mercaptans) can oxidize to disulfides if aerated. Problematically, once oxidized, these compounds cannot be removed by copper fining, as they do not react with copper.

​Drawbacks
Improper addition can cause copper casse.

 Activated Carbon (Purified Charcoal)

Process

• Dosage
  • White wine dosage: 50 – 2000 mg/L
  • Red wine dosage: 50 – 2000 mg/L
  • Odor removal: 50 to 500 mg/L
  • Color removal: 100 to 2000 mg/L
• The type of carbon (decolorizing or deodorizing) is selected depending on the usage, and it may be used in conjunction with PVPP for either task.
• Carbon is weighed out, then can be directly added to the wine in powdered form, or can be made into a slurry before addition.
• A few days are allowed for settling before the wine is filtered with an earth or pad filter.

Mechanisms

• Activated carbon is physically or chemically treated to create microfissures with high amounts of surface area and give it an electrical charge with an oxidizing property. These microfissures are what adsorb particles in wine.
• Decolorizing carbons often selectively remove flavonoid monomers and dimers. Larger polymers poorly penetrate the micropores of the carbon fragments. [15]

Benefits

• Color Removal: High. Especially used to reduce pinking and browning.
• Tannin Removal: Low
• Clarity and Stability: High
• Other Notes
  • Adsorbs a wide range of polar compounds, especially phenols and their derivatives.
  • Effective in removing off-odors, especially mercaptan off-odors.

Challenges

• In wine, it has a high tendency to over-fine. It is also regarded as a severe and relatively non-specific fining agent, therefore should be used with care.
• Can negatively decolorize wine.

Gum Arabic [17]
Made from the resin of Acacia senegal and Acacia seyal, tree gum arabic is made up of many different saccharide units, which vary by origin of wood, forest climate, and processing methods. Generally, it consists of saccharides of arabinose, rhamnose galactose, and glucuronic acids as well as amino acids including hydroxyproline, serine, threonine, proline, leucine, histidine, and aspartic acid.

Process
(for Flashgum R Liquide from Scott Labs) [18]

• Dosage: 40-120 mL/hL
• Flashgum R Liquide should be the last commercial product added to the wine. It is best to do inline additions 24-72 hours prior to the final pre-membrane and membrane filtrations. If using on wine that is not going to be filtered, add Flashgum R Liquide just prior to bottling.

Mechanisms: Surrounds the surface of colloidal matter, preventing its aggregation. Similarly, mannoproteins, another protective colloid, can be found combined with gum arabic, as is the case of UltiMA Soft by IOC.

Benefit

• Reduces astringency and increases mouthfeel.
• In red wines to be consumed young, it stabilizes anthocyanins, reduces tannin astringency, and increases the perception of body and acid.
• In sparkling wines, it can reduce the surface tension of the wine, which leads to increased fizzing.
• To inhibit tartrate crystal growth when cold stabilization is not possible, metatartaric acid and gum arabic can be used in combination to extend the stability from one year to two. However, as metatartaric acid slowly hydrolyzes into tartaric acid, inhibition potential diminishes and the potential of tartrate formation increases.
• Can be used with citric acid as a stabilizing agent to prevent ferric casse in high-iron content wines.

Challenges

• Can cause filtration issues.
• In reds which will be bottle-aged, it will restrict the desirable polyphenol chemical reactions and can create a milky appearance that can affect normal clarity.

For an insightful article on gum arabic, read:
Pambianchi, D. (2021, October 27). Gum Arabic: Winemaking's Secret Weapon. WineMakerMag.com. Retrieved May 20, 2022, from https://winemakermag.com/technique/gum-arabic-winemaking-secret-weapon

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​Clarification

​The macro process of separating solids from liquids, and unlike fining or filtration, the removed solids are almost exclusively those that are visible. Clarification typically occurs at two points during winemaking: Before fermentation of white grapes, and after fining of all grapes. The processes can be the same, however. Techniques for clarification include:

• Racking
• Flotation
• Centrifugation
  

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Racking
The process of spontaneous precipitation and natural gravity settling before separation by transferring wine from a settling container to a different container with minimal agitation to avoid resuspending particulate matter. It is not used for wines bottled a few weeks or months after fermentation, as the time required is too slow for adequate clarification.

Differences between racking techniques

• Manual draining uses gravity or a hand pump.
• Mechanical pumping allows for more precise aeration and sulfiting but has a higher equipment cost.
• Larger storage vessels require more frequent racking to avoid the development of a thick sediment layer that may cause off-odors in the wine.
• Small cooperage is generally more effective in clarifying wine.

Process
Pre-fermentation settling
(débourbage) and racking
Prior to fermentation of white and rosé wines it reduces solids content to 60-250 NTUs, or 1-2%. Freshly pressed juice contains up to 20% solids consisting of small particles of cellulose, hemicellulose, pectin, mineral salts, lipids, and proteins. This reduction can help to produce fruitier wines, reduce sulfur-like off-odors, oxidative browning potential, vineyard residues, and acetic bacteria.

The first racking:

• Is often done several weeks after alcoholic fermentation, after malolactic fermentation, or after sur lies maturation, depending on what process is used last.
• Removes most of the yeast, bacterial, and grape-cell fragments that have settled out.

Subsequent racking

• Removes most of the residual microbial population, along with precipitated tannins, pigments, and crystalline material.
• Later rackings remove sediment generated as a consequence of fining.
• The number of rackings also varies considerably from region to region and is often dependent on regional practices (Wine Science).
• Decanting stops when unavoidable turbulence makes the wine cloudy. The residue may be filtered to retrieve wine otherwise lost with the lees.

Benefits beyond clarification

• Enhances microbial stability by removing microbial cells and other nutrients conducive to microbial growth.
• Mixes the wine as it is being transferred between containers. This prevents any stratification or layers that may cause variations in flavors, particularly in large storage tanks.
• Removes the primary sources of reductive-sulfur taints, including hydrogen sulfide and mercaptans, which may form under the low-redox conditions that develop in thick layers of lees.
• Aeration/oxygen exposure can occur if desired. To prevent oxygen exposure, the pumping system can use a blanket of nitrogen.
• Releases any built up CO2 from fermentation.

Flotation/Reverse Settling (Pre-fermentation Clarification) [21]
​
The pre-fermentation clarification process typically uses nitrogen bubbles to float the solids away from the liquids, thereby speeding up the process of traditional settling and racking. In Australia, it is a common practice for wineries producing more than 1,000 tonnes.22

Process:

• Grapes are pressed and/or crushed, then pumped into a holding tank, where they are treated with pectic enzymes for 4-6 hours. When grapes are pressed, pectin is released into the must and, if not broken down, can prevent settling.
• The treated must is then transferred to the flotation tank, where flocculation aids like bentonite, gelatin, PVPP, or chitosan are added to assist in aggregating the solids and enhance gas bubble-particle interaction. Then air or nitrogen is pumped from the bottom of the tank before being racked into another tank for fermentation (~16 °C). Nitrogen will be used if reductive winemaking techniques are desired. Air can be used to hyper oxidize the wine, thereby reducing browning potential.
• Microbubbles (air, nitrogen, or oxygen) are injected into the juice. The gas causes suspended solids to rise to the surface where they can be skimmed off. Flocculation aids like bentonite and gelatin can assist in aggregating the solids and enhance gas bubble-particle interaction.23

Benefits

• Juice quickly clarifies, relative to traditional racking.
• The juice does not need to be chilled for the process to occur, which results in energy savings.
• The clarified juice can be directly inoculated at the post-floating temperature.
• Enhanced control over the degree of clarification.

Drawbacks
Few risks, with the biggest risk being excessive foaming if the flow rate of nitrogen gas is not managed correctly.

For more, read: www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-juice-clarification-by-flotation/

Centrifugation
Wine or juice is rotated at high speed in a centrifuge to speed up settling times.

Process

• Pre-fermentation clarification of white grape juice.
• Post-fermentation clarification of wine to remove lees.
• It may be more ideal for its usage in the clarification of wine than juice as there is a greater density between yeast cells and liquid than there is between grape solids and liquid.24

Benefits

• Exponentially speeds up the settling process.
• Minimizes losses from clarification due to wine binding to the filtration medium.
• Can be cost-effective if used to process a high ​enough volume of wine, due to automation and minimization of wine loss. 
• Has the least impact on the chemical composition of the juice, relative to other clarification techniques.
• Reduces potential off-odors that may develop in racked wine with significant particulate matter.
• More efficient in removing large amounts of particulates than plate filters.
• Avoids potential health problems (dust and worker allergy) associated with the use and disposal of diatomaceous earth and other filter aids.

Drawbacks

• High capital cost.
• Can use a lot of electricity.​

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​Microbial Stabilization

Long-term microbial stability is essential to preventing unwanted changes in the bottle. The probability of microbial instability varies by wine style, as there are co-factors including pH, ABV, and residual sugar content. For example:

• Sweet wines that have high residual sugar content have an increased risk for microbial growth. This can be controlled by fortification with high proof alcohol to raise the overall ABV or sterilization.
• Higher tannin concentration, wines have antimicrobial properties.
• Red wines are typically more microbial stable than white wines as they have higher alcohol content and higher tannin concentrations. This decreases the need for sterilization.
• The microbial stability of white wines vary, as the acidity of the wine made by reductive techniques has a lower pH (more acidic) than oxidative, barrel aged, and malolactic fermented white wines.

• Physical Tecniques
• Chemical Tecniques

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Physical Techniques
After racking, the following physical techniques provide long term microbial stability.

Membrane filters with a pore size of 0.45 μm or less remove yeast and bacteria that can cause instability in wine. This technique has generally replaced pasteurization, because it results in few physical or chemical disruptions to the sensory characteristics of wine. For more on this concept, see the next section on filtration.

Pasteurization [25] 

• Effective against: All microbes.
• Process: Heat wine to approximately 72 °C (161.6 °F) for 20-30 seconds before cooling it just as quickly.26
• Benefits: If done before bottling, this can promote protein and copper casse stabilization by denaturing and precipitating the colloidal proteins, allowing for their removal. However, it may generate increased amounts of protective colloids, cause slight decolorization, and modify wine aroma (Jackson, Wine Science).
• Drawbacks: Depending on the process, pasteurization can cause aroma compounds to volatilize. However, there are studies which show no loss in aroma through heating, including the following recommendation from the Australian Wine Research Institute: www.awri.com.au/wp-content/uploads/2019/10/242-October-2019-Technical-Review-McRae.pdf

Filtration
See the following section on Filtration
​

Chemical Techniques [27]
Chemical microbial stabilization has varying degrees of effectiveness. Physical microbial stabilization is significantly more effective. According to Maria Peterson, Filtration Specialist at Scott Labs, chemical treatment can be more ideal than filtration when the beverage is colloidally dramatic, therefore very difficult to filter through a final sterilization membrane, or when the microbial load is very low. For example, for Velcorin (a Scott Labs DMDC microbial control agent) to be effective the load needs to be under 500 cfu/ml.

​Sulfur dioxide

• Effective against: Bacteria
• Process
  • Added at various times during wine production, but almost always after fermentation.
  • Concentration depends on the pH, temperature, ethanol content, grape harvest practices, fermentation practices, concentration of dissolved oxygen, wine style, and cultivar.
  • For more on sulfur dioxide usage, see: hawaiibevguide.com/wine-fermentation

Sorbic acid

• Effective against: Fungi. Has the advantage of not diminishing over time. It can also be used to remove mineral deposits.
• Process: Generally, a fungistatic dose in the presence of ethanol and sulfur is roughly 200 mg/L.
• Not as effective against: Some lactic acid bacteria which can metabolize sorbic acid to sorbyl alcohol.
• Drawback: Oenococcus can esterify it into sorbyl alcohol. It then has the tendency to rearrange and become 2 ethoxy hexa-3,5-diene, which has an unpleasant, geranium-like odor. Additionally, while sorbic acid has subtle sensory characteristics, a portion of the population finds it particularly offensive.

Dimethyl dicarbonate (DMDC)

• Effective against: Yeast. including Brettanomyces.
• Process: DMDC should be added just before the filler bowl in the bottling sequence at a maximum of 200 mg/L (in Australia and New Zealand).
• Not as effective against: Bacteria
• Drawback:
  • Rapidly decomposes to carbon dioxide and methanol (within 1 hour at 30 °C and within 5 hours at 10 °C),
  • Special dosing machine is needed, due to safety and reactivity issues.

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​Filtration

*For an explanation of the filter types and methodologies, read: The Science of Filtration

Turbidity

• After Fermentation: 200+ turbidity units (NTU)
• After clarification: 100-200 NTU
• After post-clarification filtration: 1-20 NTU (wines are considered ‘cellar bright,’ or visually clear to the eye at below approximately 30 NTU)

​After cross-flow filtration or membrane filtration:

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• Filtration Process
• Wine Filterability Factors

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Filtration Processes

Post-Clarification Filtration
(Macro Filtration)
Once the fining agent is flocculated out, there can still be particulates that were not removed by clarification.

Filter: Depth filtration by:

• Traditionally a plate-and-frame/filter press.
• Lenticular filters have become more common.
• Diatomaceous earth filters (both candle filters and leaf filters) are less common.
• Filter Media: Typically cellulose, with the option for diatomaceous earth and carbon filtration.

Removes

• Fining agent
• Other compounds, including tartrate crystals.

Pre-filter

• Filter: Depth filtration by Cartridge filter
  
• Filter Media: Polypropylene (heat blown).
  
• Removes: Escaped filter media and particulates that have escaped by accidental unloading.

Membrane Filtration
Since wine is not typically pasteurized, sterile filtration removes unwanted microorganisms to prevent undesired changes in the bottle. As of 2018, approximately 80% of all wine is sterile-filtered (AWRI - Filtration).

Filter: Cartridge filter: AWRI notes that a lenticular filter followed by a .65 micron membrane and a .45 micron membrane is a common filtration setup.

Filter Media: PES or PVDF
Compounds being removed:

• Yeast
• Bacteria

Wine Recovered from Lees

• Filter: Depth filtration by rotary drum vacuum filter
• Filter Media: Diatomaceous earth
  
  
• Filter: Membrane filtration by cross-flow filter with specialized adaptations, including: wider-bore capillaries, brushing/sweeping systems at capillary inlets, and rotary pre-screens to remove coarse contaminants like seeds.
• Filter Media: Stainless steel or ceramic membranes.

Reverse Osmosis to Remove Various Compounds
Filter: Cross-flow filter is typical.
Filter Media: 0.001 μm membrane of symmetrical PES or PVDF.
Compounds being removed:

Dealcoholization
Additional steps: When alcohol is removed, water is also inevitably removed. Therefore, the wine must be reconstituted by adding in water. In some setups, the azeotropic mixture of water and alcohol is then distilled to recover the water, which is added back to the wine, and the distilled spirit can be used for something else.

Smoke taint
Additional steps: After the permeate of water, alcohol and smoke taint is removed, carbon filters are used to remove the smoke taint. The alcohol and water is then added back into the wine.
For more insight into smoke taint, read:
Mirabelli-Montan YA, Marangon M, Graça A, Mayr Marangon CM, Wilkinson KL. Techniques for Mitigating the Effects of Smoke Taint While Maintaining Quality in Wine Production: A Review. Molecules. 2021; 26(6):1672. https://doi.org/10.3390/molecules26061672
Volatile Acidity (VA)
Additional steps: After the permeate of water, alcohol and VA are removed, ion exchange canisters are used to remove the VA, and the water and alcohol are added back to the wine.
For more insight into the reverse osmosis process of wine, read:
Smith, C. (2017, January). Wines & Vines - Selecting a Machine for Reverse Osmosis. Wines Vines Analytics. Retrieved May 27, 2022, from winesvinesanalytics.com/sections/printout_article.cfm?content=178257&article=feature

​Wine Filterability Factors

​Beyond turbidity, wine filterability is impacted by a few different factors, which include:

Colloids
These unstable particles can form the characteristic gelatinous aggregates present colloidally in juice and wine, and are influenced by the grape variety, growing season, enzyme usage, fining practices, pre- and post-fermentation, residual fining agents, yeasts, bacteria, temperature, carbon dioxide, and thermal treatment.

​Though colloids can be problematic, their impact can be mitigated through the usage of enzymes to degrade them. These enzymes are often derived from Aspergillus niger, a mold commonly found on grapes, and include:

Glucans (a polysaccharide)

• Source: Produced as a result of Botrytis growth on grapes, as well as from spoilage lactic acid bacteria.
• Enzymatic treatment: Glucanase and heat treatment. This can take 6-8 weeks.
  ​

Pectins

• Source: Structural components of plant cell walls.
• Enzymatic Treatment: Pectolytic enzyme. This action is slow and costly, however.

​Polyphenols, including tannins

• Source: Grape skins.
  
  

Yeast and bacteria have a very strong positive charge and might be clinging to negatively charged polyphenols. The bond is intensified by sugar addition.
Some grapes are more “colloidally dramatic.” These include Pinot Noir and Zinfandel.

• Association colloids: Aggregates of small molecules through Van der Waals forces, hydrogen bonding, hydrophobic interactions, and the natural and fining process (Bowyer and AWRI, 2021).

Filtration Temperature
Filtration is easier at higher temperatures. Filtration at temperatures between 8 and 12 °C doubles the difficulty compared with filtration at 20 °C. It is recommended to aim for filtration at 15-21 °C, or around 18 °C.

Post-Filtration Steps
After sterile filtration, wine is immediately bottled or packaged. If wine is sweetened, the AWRI recommends bottling within a week of sweetening.
In a future issue, we will discuss the impact of bottles and bottle-aging of wine, as these also have profound effects on the wine’s final aroma.

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​Resources and Suggested Reading Resources

1.  Cold stabilisation. The Australian Wine Research Institute. (2021, July 2). Retrieved May 26, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/pre-packaging-preparation/cold-stabilisation/

2. Gardner, D. M. (2016, May 31). Cold Stabilization Options for Wineries. Penn State Extension. Retrieved May 19, 2022, from https://extension.psu.edu/cold-stabilization-options-for-wineries

3. Stars Electro-Dialysis. Vintech Pacific. (2020, December 21). Retrieved May 26, 2022, from https://www.vintechpacific.co.nz/technology-services/stabilization-technologies/stars-electro-dialysis

4. Calcium instability. The Australian Wine Research Institute. (2020, July 7). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/hazes_and_deposits/calcium_instability/

5. Crystalline Deposits. The Australian Wine Research Institute. (2020, July 7). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/hazes_and_deposits/crystalline_deposits/

 6. Iron-Induced Instability. The Australian Wine Research Institute. (2019, March 4). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/hazes_and_deposits/iron_induced_instability/

7. Trela, Brent. (2010). Iron stabilization with phytic acid in model wine and wine. American Journal of Enology and Viticulture. 61. 253-259. Retrieved from: www.researchgate.net/publication/258567104_Iron_stabilization_with_phytic_acid_in_model_wine_and_wine​

​8. Copper. The Australian Wine Research Institute. (2022, May 4). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/frequently_asked_questions/copper/

9. Removal of volatile sulfur compounds. The Australian Wine Research Institute. (2022, March 27). Retrieved May 20, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/pre-packaging-preparation/removal-volatile-sulfur-compounds/

10. Zoecklein, D. B. (n.d.). Wine Proteins and Protein Stability . Retrieved May 26, 2022, from https://www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Wine%20Proteins%20wm_20and%20Protein%20Stability.pdfand%

11. Van Sluyter, Steve & Mcrae, Jacqui & Falconer, Robert & Smith, Paul & Bacic, Antony & Waters, Elizabeth & Marangon, Matteo. (2015). Wine Protein Haze: Mechanisms of Formation and Advances in Prevention. Journal of agricultural and food chemistry. 63. 10.1021/acs.jafc.5b00047. Retrieved from: www.researchgate.net/publication/274642232_Wine_Protein_Haze_Mechanisms_of_Formation_and_Advances_in_Prevention

12. Fining agents. The Australian Wine Research Institute. (2022, May 9). Retrieved May 19, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/frequently_asked_questions/fining_agents/

13. Ruediger, G.A. & Pardon, Kevin & Sas, Alex & Godden, P.W. & Pollnitz, Alan. (2004). Removal of pesticides from red and white wine by the use of fining and filter agents. Australian Journal of Grape and Wine Research. 10. 8-16. Retrieved May 20, 2022, from https://onlinelibrary.wiley.com/doi/full/10.1111/j.1755-0238.2004.tb00003.x

14. Zoecklein, B. (1998). Bentonite Fining of Juice and Wine . Retrieved May 19, 2022, from www.apps.fst.vt.edu/extension/enology/downloads/bentonite01.pdf

15. Mustapha, D., Bouchekara, M., Fatiha, D., & Djafri, A. (2012, July). (PDF) adsorption of phenol on natural clay. researchgate.net. Retrieved May 20, 2022, from https://www.researchgate.net/publication/236866770_Adsorption_of_phenol_on_natural_clay

16. Fermenting on Bentonite. Scott Labs. (2021, July). Retrieved May 19, 2022, from https://scottlab.com/how-to-ferment-wine-on-bentonite-fermobent

17. Pambianchi, D. (2021, October 27). Gum Arabic: Winemaking's Secret Weapon. WineMakerMag.com. Retrieved May 20, 2022, from https://winemakermag.com/technique/gum-arabic-winemaking-secret-weapon

18. Flashgum R Liquid. Scott Laboratories. (n.d.). Retrieved May 26, 2022, from https://shop.scottlab.com/fining-stability/product-source=gum-arabic/flashgum-r-liquid-flashgumr?returnurl=%2Ffining-stability%2Fproduct-source%3Dgum-arabic%2F

19. FINING & STABILITY: Silica Gel. Scott Laboratories. (n.d.). Retrieved May 20, 2022, from https://shop.scottlab.com/fining-stability/

20. Removal of volatile sulfur compounds. The Australian Wine Research Institute. (n.d.). Retrieved May 20, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/pre-packaging-preparation/removal-volatile-sulfur-compounds/

21. Wineaustralia.com. (2019, September 13). Is it good night for bentonite? Wine Australia. Retrieved May 20, 2022, from https://www.wineaustralia.com/news/articles/is-it-good-night-for-bentonite

22. Winemaking treatment . The Australian Wine Research Institute. (2022, May 3). Retrieved May 26, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-juice-clarification-by-flotation/

23. Nordestgaard, S. 2019. AWRI Vineyard & Winery Practices Survey. https://& https://www.awri.com.au/wp-content/uploads/2019/05/AWRI_Practices_Survey_Final_Report.pdf

24. Scott Labs. (2021, June). Retrieved May 26, 2022, from https://scottlab.com/juice-clarification-settling

25. Robinson, J., & Harding, J. (Eds.). (2015). The Oxford companion to wine. American Chemical Society.

26. 242 technical review October 2019 . The Australian Wine Research Institute. (2019, October). Retrieved May 20, 2022, from https://www.awri.com.au/wp-content/uploads/2019/10/242-October-​2019-Technical-Review-McRae.pdf 

​27. Flash pasteurization. Vins De Bordeaux . (n.d.). Retrieved May 20, 2022, from https://www.bordeaux.com/us/Our-know-how/glossary-f/flash-pasteurization

28. Chemical Options for microbiological stabilisation. The Australian Wine Research Institute. (2021, April 15). Retrieved May 20, 2022, from https://www.awri.com.au/industry_support/winemaking_resources/storage-and-packaging/pre-packaging-preparation/microbiological-stabilisation/

29. Hakim, S. (2018, April 3). Sorbic acid. Viticulture and Enology. Retrieved May 20, 2022, from https://wineserver.ucdavis.edu/industry-info/enology/methods-and-techniques/common-chemical-reagents/sorbic-acid

30. Australian Wine Research Institute (Director). (2021). Filtration, filterability and facts [Film]. www.youtube.com/watch?v=4FhDKnriroA

31. Australian Wine Research Institute. (2016, March 2). Winemaking - Winery lees: Minimising volumes and recovering better quality juice and wine. The Australian Wine Research Institute. Retrieved May 27, 2022, from www.awri.com.au/wp-content/uploads/2016/05/Lees-article.pdf

32. Winesecrets (Director). (n.d.). Wine Alcohol Removal by Reverse Osmosis [Film]. https://youtu.be/h_3EDUZyICs

33. Gitsov, I. P. I. (2019). Mitigation of Smoke Taint in Wine (Doctoral dissertation, Washington State University). https://www.asev.org/abstract/reverse-osmosis-method-mitigating-smoke-taint

34. Winesecrets (Director). (2017). Wine VA Reduction by Reverse Osmosis [Film]. www.youtube.com/watch?v=MZSSlAUjj90

35. Zoecklein, B., Fugelsang, K. C., Gump, B. H., & Nury, F. S. (2013). Wine analysis and production. Springer Science & Business Media. Retrieved from: https://www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Winery%20Filtration.pdf

36. Duane, J. (2019, August 19). 97: Filtration featuring Maria Peterson from Scott Labs — Inside Winemaking. Inside Winemaking. Retrieved May 27, 2022, from www.insidewinemaking.com/097/filtration-maria-petersoncom/peterson