Clarification and stabilization of wine
Encyclopedia
The clarification and stabilization of wine in winemaking
involves removing insoluble and suspended
materials. The insoluble material causes a wine
to be cloudy. These processes may include fining, filtration
, centrifugation
, flotation
, refrigeration
, barrel maturation, pasteurization
and racking
. Most of these processes will occur after the primary fermentation
and before the wine is bottled. The exception is for white wine production which will usually have the must
separated from some of the grape skins and particles prior to fermentation so as to avoid any unwanted maceration
. The timing and exact methods used will vary by producer, depending on the desired finish product -- such as a completely bright and clear wine or a wine that still retains some of the flavor and color phenols. Some of the materials that are removed from the must during this stage of winemaking include dead yeast
cells (lees), bacteria, tartrate
s, protein
s, pectin
s, various tannins and other phenolic compounds, and pieces of grape skins, pulp
, stems and gum
s.
, a wine is considered "clear" when there are no visible particles suspended in the liquid and (mostly in regards to white wines) there is some degree of transparency. This is demonstrated by holding the glass up to a piece of paper with writing and seeing if one could read through the wine. Some red wine grape varieties have a naturally high concentration of coloring phenols that make the wine more translucent or opaque
. For these wines, the brightness or "vividness" of the wines color is considered. A wine with a lot of suspended particles will appear less clear and more dull in brightness. While lack of clarity and brightness may not negatively affect the taste of wine, it may make the wine less visually appealing to the consumer. In the modern wine industry there has been a premium placed on wines being both clear and bright. To achieve this, wines are usually clarified through some means in order to remove suspended particles.
These suspended particles are normally insoluble solids such as lees, fragments of grape skins, pulp and seeds as well as colloids that are not visible to the unaided eye like gums, pectins, proteins, tartrates, active yeast and bacteria. The forces of gravity can achieve natural clarification through the process of settling
(French
débourbage) where the larger suspended particles gradually settle to the bottom of the storage vessel. The wine is then siphoned or "racked" off the compact solids into a new container. This natural process can be very lengthy, sometimes requiring many months or even a couple years as well as several rackings in order to produce a perfectly clear wine. Producers can accelerate the process by using fining agents, filtration or flotation.
The timing of these methods vary depending on producer and type of wine being made. White wine, particularly aromatic varieties such as Riesling
and Sauvignon blanc
, is often settled and racked soon after the grapes are crushed and pressed. This is to minimize maceration
and exposure to the phenolic compounds present in the grapes' skin, seeds and stems that can leach out into the must and cause the wine to prematurely brown in color as well as diminish the fruit flavors of the wine. Other varieties, such as Chardonnay
, may spend some time in contact with the skins and particulate matter in order to gain complexity before being settled and racked. To aid in this clarification of white wine, pectin-splitting enzyme
s, sulfur dioxide
and fining agents such as bentonite
are added to the must to encourage the agglomeration
and settling of the colloids while the holding tank is brought to low temperatures and held for 24 hours prior to rack. While most red wines are clarified after fermentation, the pectin-splitting enzymes may be added prior to fermentation to make post-fermentation clarification easier.
In winemaking, fining is the process where a substance (fining agent) is added to the wine to create an adsorbent, enzymatic or ionic bond
with the suspended particles, making them a larger molecule that can precipitate out of the wine easier and quicker. Unlike filtration, which can only remove particulates (such as dead yeast cells and grape fragments), fining is effective in removing soluble substances such as polymerized tannins, coloring phenols and proteins
. Given enough time in a stable environment, many of these suspended particles would gradually precipitate out on their own. The use of fining agents speeds up the process at lower cost. White wines are fined to remove particles that may cause the wine to brown or lose color as well as removing heat-unstable proteins that could cause the wine to appear hazy or cloudy should it be exposed to high temperatures after bottling. Red wines are fined for the same reason but also for the added benefit of reducing the amount of bitter, astringent tannins which makes these wines smoother and more approachable sooner after bottling and release. Throughout history a wide range of substances have been used as fining agents, such as dried blood
powder
, but today there are two general types of fining agents — organic compounds and solid/mineral materials.
Organic compounds used as fining agents are generally animal based, which may bring concerns for a vegan diet. The most common organic compounds used include egg white
s, casein
derived from milk
, gelatin
and isinglass
obtained from the bladders of fish
. Pulverized minerals and solid materials can also be used as fining agents with bentonite
clay being one of the most common fining agent used due to its effectiveness in absorbing proteins and some bacteria. Activated carbon
derived from charcoal
is used to remove some phenols that contribute to browning colors as well as some particles that produce "off-odors" in the wine. In a process known as blue fining, potassium ferrocyanide
is used to remove copper
and iron
particles that may have entered the wine through the use of metal winery and vineyard equipment, vineyard sprays such as the bordeaux mixture
, and the use of bentonite as a fining agent . Due to the potential of potassium ferrocyanide forming hydrogen cyanide, its use is highly regulated and is illegal in many wine producing countries. Other inorganic materials use include silica and kaolin.
Some countries, such as Australia and New Zealand, have wine label
ing laws that require the use of fining agents that may be an allergenic substance to appear on the wine label, as there may be trace amounts of the substance still in the wine. However a study conducted by the University of California, Davis Department of Viticulture and Enology found that no detectable amount of inorganic fining agents such as bentonite are present in wine that has been fined and only negligible trace amount of proteinaceous agents such as egg white
s can be detected.
As with filtration, there is the risk of some loss of flavor with fining due to desirable flavor molecules being precipitated out along with the more undesirable particles. Some producers of premium wine will do less fining or do it much later in the production process in order to leach as much flavor and aromatics from the phenols before they are removed. Still, fining is considered a less harsh process than filtration, with its advocates believing that it better mimics the natural clarification and stabilization process.
While fining clarifies wine by binding
to suspended particles and precipitating out as larger particles, filtration works by passing the wine through a filter medium that captures particles that are larger than the hole size of the medium. Complete filtration may require a series of filtering through progressively finer filters which can be expensive but will be considerably quicker than letting gravity naturally settle the wine and using racking to siphon the clear wine out. Most filtration in a winery can be classified as either depth filtration or surface filtration.
Depth filtration is often the first type of filtration a wine sees after fermentation when the wine is pushed through a thick layer of pads made from cellulose
fibers, diatomaceous earth
or perlite
which traps the particles and can be removed from the wine. If the producers wish to further filter the wine, they may go to surface filtration. Surface filtration involves running the wine along a thin film of polymer
material filled with holes tinier than the particles that are being filtered out. Running the wine parallel
to filter surface (known as "Cross-flow"
surface filtration) will minimize the amount of potential clogging of the filter. Most membranes are made from plastic or ceramic
. Another step in surface filtration, usually taking place right before bottling, is microfiltration
where the fine is passed through a membrane with holes small enough to trap yeast and bacteria cells. An alternative to filtration is centrifugation
where wine is put through a centrifuge
decanter and gravity separates the particles from the wine.
The use of filtration is a controversial subject in winemaking with some producers feeling that the technique strips the wine of too much of its natural flavors and characteristics. Some producers will add the phrase "unfiltered" to their wine label as a marketing tool. Wine can go through a natural clarification and stabilization process by aging in a wood barrel where the subtle oxidative effects can aid in the precipitation of larger particles (particularly proteins, tartrates and malate
s). This process takes time, however, and producers who bottle their wine too early, and without the assurance of sterile bottling equipment, can risk microbial contamination and instability. Wines that have not been filtered are much more likely to develop sediment as the wine ages.
process used in the mining
industry for ore
refining
. In this process, small bubbles of air (or compressed nitrogen
) are injected into the bottom of a tank. As the bubbles rise through the must, grape solids have a natural tendency to cling to the bubbles creating a froth that can be removed from the wine. This technique has to take place prior to fermentation since the biological activity of yeast cells serves as an inhibitor to the flocculation
needed for the froth to form. Since phenolic compounds that are prone to oxidation and browning are highly reactive to the air bubbles, wines that have gone through the flotation process are often more resistant to oxidative browning if exposed to air later.
As a chemical substance dependent on the activity of microorganisms and complex chemical reaction, wine can be very unstable
and reactive to changes in its environment. After bottling, a wine can be exposed to extremes in temperatures and humidity
as well as violent movement during transportation and storage that can encourage the wine to go through additional chemical changes that may produce faults or undesirable traits to emerge in the wine. These can include carbonic gas, formation of sediment deposits or tartrate crystals, hazy or cloudy appearance, rapid deterioration of flavor and spoilage. Eliminating suspended particles in a wine can increase the stability of a wine and prevent some of these undesirable characteristic to emerge. The process of clarification does, in itself, increase the stability of the wine by removing some of these particles. Conversely, the process of stabilization can also increase the clarity and brightness of a wine.
with the majority of the concentration present as potassium acid salt. During fermentation, these tartrate
s bind with the lees, pulp debris and precipitated tannins and pigments. While there is some variance among grape varieties and wine regions, generally about half of the deposits are soluble in the alcoholic mixture of wine. The crystallization
of these tartrates can happen at unpredictable times if the wine is exposed to low temperature. These crystals can appear in a wine bottle looking like broken glass (though they are in fact harmless) and their presence may be undesirable to consumers. To prevent this from happening after the wine has been bottled, winemakers stabilize the wine by putting it through a cold stabilization process where it is exposed to temperatures below freezing to encourage the tartrates to crystallize and precipitate out of the wine. Some white grape varieties (such as Muscat) have significant quantities of proteins that are "heat-unstable" and will coagulate if the wine is exposed to excessive amount of heat fluctuations, making the wine appear hazy and cloudy. Winemakers will use fining agents, such as bentonite, to remove these proteins and increase the heat stability of the wine.
Both active yeast cells and bacteria may be present in a wine after it has gone through the fermentation process and is bottled. If the wine still contains some residual sugar, the active yeast cells will initiate a secondary fermentation
process inside the bottle that will create dissolved carbonic gas as a by-product. When the wine is opened, it will be gassy or "sparkling". While this may be a desirable trait for some wines (such as Champagne where a deliberate initiation of a secondary fermentation is part of production
), it is not desirable for wines intended to be still or non-sparkling--such as Burgundy Pinot noir
or a Washington Merlot
. The easiest way to stabilize the wine is to ensure that there is no fermentable sugars
left in the wine but in cases where some residual sugar in desirable (such as to balance the acidity of the wine
) other methods can be taken to stabilize the wine. One method is sterile filtration and bottling which ensures that no active yeast are present in the wine. Another method is the addition of sulfur dioxide and sorbic acid
which can inhibit the growth of yeast cells.
Modern advances in hygiene
has eliminated many of the bacterial concerns that contribute to wine stability. Historically the presence of bacteria played a larger role in the developing of various wine faults. The primary concern in modern wineries is the presence of acetobacter
which can turn wine into vinegar
and lactic acid bacteria
that can initiate malolactic fermentation
which may not be desirable for certain wines. Acetobacter is active in the presence of oxygen so taking preventative measures, such as the use of sulfur dioxide, can suppress the growth of acetobacter. Eliminating the presence of fermentable sugars and malic acid
can inhibit the growth of lactic acid bacteria and stabilize the wine.
s, the production of mevushal wines (literally "cooked" or "boiled") heat sterilizes the wine to where non-Jews and non-observant Jews can handle the wine and still maintain its kosher status. In the process of pasteurization, wines are brought up to temperatures of 185 °F (85 °C) for a minute and then quickly cooled to a temperature of 122 °F (50 °C) where it is kept for up to 3 days. The wine may then be allowed to cool down to room temperature or be bottled "hot" and cooled by water sprays. This process can be rough on a wine and could diminish flavors and aging potential. A more gentle procedure known as flash pasteurization
has been developed which heats the wine to 205 °F (95 °C) for a few seconds, followed by rapid cooling.
, notes that techniques like filtration can improve wine quality in moderation but can also diminish quality if used excessively. The consumers of some premium wines (such as Bordeaux and Port) may expect to see tartrates and sediment from a wine that has been aging and not thoroughly filtered.
Winemaking
Winemaking, or vinification, is the production of wine, starting with selection of the grapes or other produce and ending with bottling the finished wine. Although most wine is made from grapes, it may also be made from other fruit or non-toxic plant material...
involves removing insoluble and suspended
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...
materials. The insoluble material causes a wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...
to be cloudy. These processes may include fining, filtration
Filtration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
, centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...
, flotation
Flotation process
Flotation process is a method of separation widely used in the wastewater treatment and mineral processing industries.Various flotation processes include the following:* Dissolved air flotation...
, refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
, barrel maturation, pasteurization
Pasteurization
Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...
and racking
Racking
Racking is the process of siphoning the wine or beer off the lees into a new, clean barrel or in the case of beer off the trub. Racking allows clarification and aids in stabilization. Wine that is allowed to age on the lees often develops "off-tastes". A racking hose or tubing is used and can be...
. Most of these processes will occur after the primary fermentation
Fermentation (wine)
The process of fermentation in wine turns grape juice into an alcoholic beverage. During fermentation, yeast interact with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide...
and before the wine is bottled. The exception is for white wine production which will usually have the must
Must
Must is freshly pressed fruit juice that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace; it typically makes up 7%–23% of the total weight of the must. Making must is the first step in winemaking...
separated from some of the grape skins and particles prior to fermentation so as to avoid any unwanted maceration
Maceration (wine)
Maceration is the winemaking process where the phenolic materials of the grape— tannins, coloring agents and flavor compounds— are leached from the grape skins, seeds and stems into the must. Maceration is the process by which the red wine receives its red color, since 99% of all grape juice is...
. The timing and exact methods used will vary by producer, depending on the desired finish product -- such as a completely bright and clear wine or a wine that still retains some of the flavor and color phenols. Some of the materials that are removed from the must during this stage of winemaking include dead yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
cells (lees), bacteria, tartrate
Tartrate
A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. Its formula is O−OC-CH-CH-COO− or C4H4O62−.As food additives, tartrates are used as antioxidants, acidity regulators, and emulsifiers...
s, protein
Proteins in wine
Proteins are present in wine. The most common proteins include thaumatin-like proteins and chitinases and have a role in the formation of turbidity especially visible in white wine. The quantity of haze forming is dependant on the quantity of phenolics in the wine.Some of those proteins are...
s, pectin
Pectin
Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It was first isolated and described in 1825 by Henri Braconnot...
s, various tannins and other phenolic compounds, and pieces of grape skins, pulp
Juice vesicles
The juice vesicles of a citrus fruit are the membranous content of the fruit’s endocarp. The vesicles contain the juice of the fruit. The pulp is usually removed from the juice by filtering it out...
, stems and gum
Gum (botany)
Gum is a sap or other resinous material associated with certain species of the plant kingdom. This material is often polysaccharide-based and most frequently is associated with woody plants, particularly under the bark or as a seed coating...
s.
Clarifying wine
In wine tastingWine tasting
Wine tasting is the sensory examination and evaluation of wine. While the practice of wine tasting is as ancient as its production, a more formalized methodology has slowly become established from the 14th century onwards...
, a wine is considered "clear" when there are no visible particles suspended in the liquid and (mostly in regards to white wines) there is some degree of transparency. This is demonstrated by holding the glass up to a piece of paper with writing and seeing if one could read through the wine. Some red wine grape varieties have a naturally high concentration of coloring phenols that make the wine more translucent or opaque
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...
. For these wines, the brightness or "vividness" of the wines color is considered. A wine with a lot of suspended particles will appear less clear and more dull in brightness. While lack of clarity and brightness may not negatively affect the taste of wine, it may make the wine less visually appealing to the consumer. In the modern wine industry there has been a premium placed on wines being both clear and bright. To achieve this, wines are usually clarified through some means in order to remove suspended particles.
These suspended particles are normally insoluble solids such as lees, fragments of grape skins, pulp and seeds as well as colloids that are not visible to the unaided eye like gums, pectins, proteins, tartrates, active yeast and bacteria. The forces of gravity can achieve natural clarification through the process of settling
Settling
Settling is the process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force...
(French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
débourbage) where the larger suspended particles gradually settle to the bottom of the storage vessel. The wine is then siphoned or "racked" off the compact solids into a new container. This natural process can be very lengthy, sometimes requiring many months or even a couple years as well as several rackings in order to produce a perfectly clear wine. Producers can accelerate the process by using fining agents, filtration or flotation.
The timing of these methods vary depending on producer and type of wine being made. White wine, particularly aromatic varieties such as Riesling
Riesling
Riesling is a white grape variety which originated in the Rhine region of Germany. Riesling is an aromatic grape variety displaying flowery, almost perfumed, aromas as well as high acidity. It is used to make dry, semi-sweet, sweet and sparkling white wines. Riesling wines are usually varietally...
and Sauvignon blanc
Sauvignon blanc
Sauvignon Blanc is a green-skinned grape variety which originates from the Bordeaux region of France. The grape most likely gets its name from the French word sauvage and blanc due to its early origins as an indigenous grape in South West France., a possible descendant of savagnin...
, is often settled and racked soon after the grapes are crushed and pressed. This is to minimize maceration
Maceration (wine)
Maceration is the winemaking process where the phenolic materials of the grape— tannins, coloring agents and flavor compounds— are leached from the grape skins, seeds and stems into the must. Maceration is the process by which the red wine receives its red color, since 99% of all grape juice is...
and exposure to the phenolic compounds present in the grapes' skin, seeds and stems that can leach out into the must and cause the wine to prematurely brown in color as well as diminish the fruit flavors of the wine. Other varieties, such as Chardonnay
Chardonnay
Chardonnay is a green-skinned grape variety used to make white wine. It is originated from the Burgundy wine region of eastern France but is now grown wherever wine is produced, from England to New Zealand...
, may spend some time in contact with the skins and particulate matter in order to gain complexity before being settled and racked. To aid in this clarification of white wine, pectin-splitting enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s, sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
and fining agents such as bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
are added to the must to encourage the agglomeration
Agglomeration
In the study of human settlements, an urban agglomeration is an extended city or town area comprising the built-up area of a central place and any suburbs linked by continuous urban area. In France, INSEE the French Statistical Institute, translate it as "Unité urbaine" which means continuous...
and settling of the colloids while the holding tank is brought to low temperatures and held for 24 hours prior to rack. While most red wines are clarified after fermentation, the pectin-splitting enzymes may be added prior to fermentation to make post-fermentation clarification easier.
Fining
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...
with the suspended particles, making them a larger molecule that can precipitate out of the wine easier and quicker. Unlike filtration, which can only remove particulates (such as dead yeast cells and grape fragments), fining is effective in removing soluble substances such as polymerized tannins, coloring phenols and proteins
Proteins in wine
Proteins are present in wine. The most common proteins include thaumatin-like proteins and chitinases and have a role in the formation of turbidity especially visible in white wine. The quantity of haze forming is dependant on the quantity of phenolics in the wine.Some of those proteins are...
. Given enough time in a stable environment, many of these suspended particles would gradually precipitate out on their own. The use of fining agents speeds up the process at lower cost. White wines are fined to remove particles that may cause the wine to brown or lose color as well as removing heat-unstable proteins that could cause the wine to appear hazy or cloudy should it be exposed to high temperatures after bottling. Red wines are fined for the same reason but also for the added benefit of reducing the amount of bitter, astringent tannins which makes these wines smoother and more approachable sooner after bottling and release. Throughout history a wide range of substances have been used as fining agents, such as dried blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
powder
Powder (substance)
A powder is a dry,thick bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material...
, but today there are two general types of fining agents — organic compounds and solid/mineral materials.
Organic compounds used as fining agents are generally animal based, which may bring concerns for a vegan diet. The most common organic compounds used include egg white
Egg white
Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...
s, casein
Casein
Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....
derived from milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
, gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
and isinglass
Isinglass
Isinglass is a substance obtained from the dried swim bladders of fish. It is a form of collagen used mainly for the clarification of wine and beer. It can also be cooked into a paste for specialized gluing purposes....
obtained from the bladders of fish
Gas bladder
The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth without having to waste energy in swimming...
. Pulverized minerals and solid materials can also be used as fining agents with bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
clay being one of the most common fining agent used due to its effectiveness in absorbing proteins and some bacteria. Activated carbon
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...
derived from charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
is used to remove some phenols that contribute to browning colors as well as some particles that produce "off-odors" in the wine. In a process known as blue fining, potassium ferrocyanide
Potassium ferrocyanide
Potassium ferrocyanide is the inorganic compound with formula K4[Fe6]•3H2O. It is the potassium salt of the coordination complex [Fe6]4-. This salt forms lemon-yellow monoclinic crystals.-Synthesis:...
is used to remove copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
particles that may have entered the wine through the use of metal winery and vineyard equipment, vineyard sprays such as the bordeaux mixture
Bordeaux mixture
Bordeaux mixture is a mixture of copper sulfate and slaked lime used as a fungicide in vineyards. It is used mainly to control garden, vineyard, nursery and farm infestations of fungi, primarily downy mildew which can result from infections of Plasmopara viticola. It was invented in the Bordeaux...
, and the use of bentonite as a fining agent . Due to the potential of potassium ferrocyanide forming hydrogen cyanide, its use is highly regulated and is illegal in many wine producing countries. Other inorganic materials use include silica and kaolin.
Some countries, such as Australia and New Zealand, have wine label
Wine label
Wine labels are important sources of information for consumers since they tell the type and origin of the wine. The label is often the only resource a buyer has for evaluating the wine before purchasing it...
ing laws that require the use of fining agents that may be an allergenic substance to appear on the wine label, as there may be trace amounts of the substance still in the wine. However a study conducted by the University of California, Davis Department of Viticulture and Enology found that no detectable amount of inorganic fining agents such as bentonite are present in wine that has been fined and only negligible trace amount of proteinaceous agents such as egg white
Egg white
Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...
s can be detected.
As with filtration, there is the risk of some loss of flavor with fining due to desirable flavor molecules being precipitated out along with the more undesirable particles. Some producers of premium wine will do less fining or do it much later in the production process in order to leach as much flavor and aromatics from the phenols before they are removed. Still, fining is considered a less harsh process than filtration, with its advocates believing that it better mimics the natural clarification and stabilization process.
Filtration
Binding (molecular)
Molecular binding is an attractive interaction between two molecules which results in a stable association in which the molecules are in close proximity to each other...
to suspended particles and precipitating out as larger particles, filtration works by passing the wine through a filter medium that captures particles that are larger than the hole size of the medium. Complete filtration may require a series of filtering through progressively finer filters which can be expensive but will be considerably quicker than letting gravity naturally settle the wine and using racking to siphon the clear wine out. Most filtration in a winery can be classified as either depth filtration or surface filtration.
Depth filtration is often the first type of filtration a wine sees after fermentation when the wine is pushed through a thick layer of pads made from cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
fibers, diatomaceous earth
Diatomaceous earth
Diatomaceous earth also known as diatomite or kieselgur/kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 1 micrometre to more than 1 millimetre, but typically 10 to...
or perlite
Perlite
Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently...
which traps the particles and can be removed from the wine. If the producers wish to further filter the wine, they may go to surface filtration. Surface filtration involves running the wine along a thin film of polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
material filled with holes tinier than the particles that are being filtered out. Running the wine parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
to filter surface (known as "Cross-flow"
Cross-flow filtration
In chemical engineering, biochemical engineering and protein purification, crossflow filtration is a type of filtration...
surface filtration) will minimize the amount of potential clogging of the filter. Most membranes are made from plastic or ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
. Another step in surface filtration, usually taking place right before bottling, is microfiltration
Microfiltration
Microfiltration is a membrane technical filtration process which removes contaminants from a fluid by passage through a microporous membrane. A typical microfiltration membrane pore size range is 0.1 to 10 micrometres...
where the fine is passed through a membrane with holes small enough to trap yeast and bacteria cells. An alternative to filtration is centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...
where wine is put through a centrifuge
Centrifuge
A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...
decanter and gravity separates the particles from the wine.
The use of filtration is a controversial subject in winemaking with some producers feeling that the technique strips the wine of too much of its natural flavors and characteristics. Some producers will add the phrase "unfiltered" to their wine label as a marketing tool. Wine can go through a natural clarification and stabilization process by aging in a wood barrel where the subtle oxidative effects can aid in the precipitation of larger particles (particularly proteins, tartrates and malate
Malate
Malate is the ionized form of malic acid. It is an important chemical compound in biochemistry. In the C4 carbon fixation process, malate is a source of CO2 in the Calvin cycle....
s). This process takes time, however, and producers who bottle their wine too early, and without the assurance of sterile bottling equipment, can risk microbial contamination and instability. Wines that have not been filtered are much more likely to develop sediment as the wine ages.
Flotation
The winemaking technique of flotation was adapted from the froth flotationFroth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries...
process used in the mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
industry for ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
refining
Refining
Refining is the process of purification of a substance or a form. The term is usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum will burn straight from the ground, but it will burn poorly...
. In this process, small bubbles of air (or compressed nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
) are injected into the bottom of a tank. As the bubbles rise through the must, grape solids have a natural tendency to cling to the bubbles creating a froth that can be removed from the wine. This technique has to take place prior to fermentation since the biological activity of yeast cells serves as an inhibitor to the flocculation
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...
needed for the froth to form. Since phenolic compounds that are prone to oxidation and browning are highly reactive to the air bubbles, wines that have gone through the flotation process are often more resistant to oxidative browning if exposed to air later.
Stabilization
Chemical stability
Chemical stability when used in the technical sense in chemistry, means thermodynamic stability of a chemical system.Thermodynamic stability occurs when a system is in its lowest energy state, or chemical equilibrium with its environment. This may be a dynamic equilibrium, where individual atoms...
and reactive to changes in its environment. After bottling, a wine can be exposed to extremes in temperatures and humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
as well as violent movement during transportation and storage that can encourage the wine to go through additional chemical changes that may produce faults or undesirable traits to emerge in the wine. These can include carbonic gas, formation of sediment deposits or tartrate crystals, hazy or cloudy appearance, rapid deterioration of flavor and spoilage. Eliminating suspended particles in a wine can increase the stability of a wine and prevent some of these undesirable characteristic to emerge. The process of clarification does, in itself, increase the stability of the wine by removing some of these particles. Conversely, the process of stabilization can also increase the clarity and brightness of a wine.
Temperature instability
Tartaric acid is the most prominent acid in wineAcids in wine
The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeasts during fermentation and protecting the wine...
with the majority of the concentration present as potassium acid salt. During fermentation, these tartrate
Tartrate
A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. Its formula is O−OC-CH-CH-COO− or C4H4O62−.As food additives, tartrates are used as antioxidants, acidity regulators, and emulsifiers...
s bind with the lees, pulp debris and precipitated tannins and pigments. While there is some variance among grape varieties and wine regions, generally about half of the deposits are soluble in the alcoholic mixture of wine. The crystallization
Crystallization
Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid...
of these tartrates can happen at unpredictable times if the wine is exposed to low temperature. These crystals can appear in a wine bottle looking like broken glass (though they are in fact harmless) and their presence may be undesirable to consumers. To prevent this from happening after the wine has been bottled, winemakers stabilize the wine by putting it through a cold stabilization process where it is exposed to temperatures below freezing to encourage the tartrates to crystallize and precipitate out of the wine. Some white grape varieties (such as Muscat) have significant quantities of proteins that are "heat-unstable" and will coagulate if the wine is exposed to excessive amount of heat fluctuations, making the wine appear hazy and cloudy. Winemakers will use fining agents, such as bentonite, to remove these proteins and increase the heat stability of the wine.
Microbiological instability
Secondary fermentation
Secondary fermentation is a process commonly associated with winemaking, which entails a second period of fermentation in a different vessel than what was used when the fermentation process first started. An example of this would be starting fermentation in a carboy or stainless steel tank and then...
process inside the bottle that will create dissolved carbonic gas as a by-product. When the wine is opened, it will be gassy or "sparkling". While this may be a desirable trait for some wines (such as Champagne where a deliberate initiation of a secondary fermentation is part of production
Sparkling wine production
There are four main methods of sparkling wine production. The first is simple injection of carbon dioxide , the process used in soft drinks, but this produces big bubbles that dissipate quickly in the glass. The second is the Metodo Italiano – Charmat process, in which the wine undergoes a...
), it is not desirable for wines intended to be still or non-sparkling--such as Burgundy Pinot noir
Pinot Noir
Pinot noir is a black wine grape variety of the species Vitis vinifera. The name may also refer to wines created predominantly from Pinot noir grapes...
or a Washington Merlot
Merlot
Merlot is a darkly blue-coloured wine grape, that is used as both a blending grape and for varietal wines. The name Merlot is thought to derive from the Old French word for young blackbird, merlot, a diminutive of merle, the blackbird , probably from the color of the grape. Merlot-based wines...
. The easiest way to stabilize the wine is to ensure that there is no fermentable sugars
Sugars in wine
The sugars in wine grapes are what make winemaking possible. During the process of fermentation, sugars are broken down and converted by yeasts into alcohol and carbon dioxide. Grapes accumulate sugars as they grow on the grapevine through the translocation of sucrose molecules that are produced...
left in the wine but in cases where some residual sugar in desirable (such as to balance the acidity of the wine
Acids in wine
The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeasts during fermentation and protecting the wine...
) other methods can be taken to stabilize the wine. One method is sterile filtration and bottling which ensures that no active yeast are present in the wine. Another method is the addition of sulfur dioxide and sorbic acid
Sorbic acid
Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula C6H8O2. It is a colourless solid that is slightly soluble in water and sublimes readily...
which can inhibit the growth of yeast cells.
Modern advances in hygiene
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
has eliminated many of the bacterial concerns that contribute to wine stability. Historically the presence of bacteria played a larger role in the developing of various wine faults. The primary concern in modern wineries is the presence of acetobacter
Acetobacter
Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. There are several species within this genus, and there are other bacteria capable of forming acetic acid under various conditions; but all of the Acetobacter are...
which can turn wine into vinegar
Vinegar
Vinegar is a liquid substance consisting mainly of acetic acid and water, the acetic acid being produced through the fermentation of ethanol by acetic acid bacteria. Commercial vinegar is produced either by fast or slow fermentation processes. Slow methods generally are used with traditional...
and lactic acid bacteria
Lactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
that can initiate malolactic fermentation
Malolactic fermentation
Malolactic fermentation is a process in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation tends to create a rounder, fuller mouthfeel. It has been said that malic acid tastes of green apples...
which may not be desirable for certain wines. Acetobacter is active in the presence of oxygen so taking preventative measures, such as the use of sulfur dioxide, can suppress the growth of acetobacter. Eliminating the presence of fermentable sugars and malic acid
Malic acid
Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. It is a dicarboxylic acid which is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms , though only the L-isomer exists...
can inhibit the growth of lactic acid bacteria and stabilize the wine.
Other methods of stabilization
The clarification methods of fining and filtration also act to stabilize wine by removing some of the same particles that can promote instability. The subtle oxidation that occurs with oak barrel aging has a naturally stabilizing effect on the wine.Pasteurization
A wine can be stabilized by a method of heat sterilization, commonly known as pasteurization. The purpose of this technique is to bring the wine up to high enough temperatures that all micro-organisms in the wine (namely yeast and bacteria) are killed. For kosher wineKosher wine
Kosher wine is grape wine produced according to Judaism's religious law, specifically, Jewish dietary laws .To be considered kosher, Sabbath-observant Jews must be involved in the entire winemaking process and any ingredients used, including finings, must be kosher...
s, the production of mevushal wines (literally "cooked" or "boiled") heat sterilizes the wine to where non-Jews and non-observant Jews can handle the wine and still maintain its kosher status. In the process of pasteurization, wines are brought up to temperatures of 185 °F (85 °C) for a minute and then quickly cooled to a temperature of 122 °F (50 °C) where it is kept for up to 3 days. The wine may then be allowed to cool down to room temperature or be bottled "hot" and cooled by water sprays. This process can be rough on a wine and could diminish flavors and aging potential. A more gentle procedure known as flash pasteurization
Flash pasteurization
Flash pasteurization, also called "High Temperature Short Time" processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, and some dairy products...
has been developed which heats the wine to 205 °F (95 °C) for a few seconds, followed by rapid cooling.
Premium wine production
Not all producers decide to thoroughly clarify and stabilize their wines, believing that some of a wine's flavor, aging potential and complexity come from some of the suspended particles. Wine experts, such as Tom StevensonTom Stevenson
Tom Stevenson is a British author who has been writing about wine for more than 30 years. Described by his colleagues as one of today’s most prolific wine authors, Stevenson is regarded as the world’s leading authority on Champagne...
, notes that techniques like filtration can improve wine quality in moderation but can also diminish quality if used excessively. The consumers of some premium wines (such as Bordeaux and Port) may expect to see tartrates and sediment from a wine that has been aging and not thoroughly filtered.