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In
winemaking Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and ...
, clarification and stabilization are the processes by which
insoluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
matter suspended in the
wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...
is removed before bottling. This matter may include dead
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
cells ( lees),
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
,
tartrate A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. The formula of the tartrate dianion is O−OC-CH(OH)-CH(OH)-COO− or C4H4O62−. The main forms of tartrates used commercially are pure crystalline ta ...
s,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s,
pectin Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component o ...
s, various tannins and other
phenolic compounds In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are c ...
, as well as pieces of grape skin, pulp, stems and gums.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition, pp. 173, 661–62. Oxford University Press 2006 . Clarification and stabilization may involve fining,
filtration Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter ...
,
centrifugation Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...
, flotation,
refrigeration The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
,
pasteurization Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life. ...
, and/or barrel maturation and
racking Racking, often referred to as Soutirage or Soutirage traditionnel (meaning racking in French), also filtering or fining, is the process of moving wine or beer from one container to another using gravity rather than a pump, which can be disruptiv ...
.


Clarifying wine

In
wine 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 onward. Modern, professional w ...
, a wine is considered " clear" when there are no visible particles suspended in the liquid and, especially in the case of white wines, when there is some degree of transparency. A wine with too much suspended matter will appear cloudy and dull, even if its aroma and flavor are unaffected; wines therefore generally undergo some kind of clarification. Before
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
,
pectin Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component o ...
-splitting
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s and, for white wine, fining agents such as
bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...
may be added to the
must Must (from the Latin ''vinum mustum'', "young wine") is freshly crushed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace and typically makes up 7–23% of th ...
in order to promote the eventual
agglomeration Agglomeration may refer to: * Urban agglomeration, in standard English * Megalopolis, in Chinese English, as defined in China's ''Standard for basic terminology of urban planning'' (GB/T 50280—98). Also known as " city cluster". * Economies of ag ...
and
settling Settling is the process by which particulates move towards 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 ...
of
colloids A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
. Pectins are structural molecules in the cell walls of fruits which have the important function of 'gumming' plant cells together. The pectin content of grapes increases steadily throughout ripening, reaching levels of about 1 g/L, although it varies by varietal and pre-fermentation handling processes. Large pectin molecules can affect the amount of juice yielded at pressing, ease of filtration and clarification, and extraction of tannins. Grapes contain natural pectolytic enzymes responsible for softening the grape berries during ripening, but these are not active under wine-making conditions (due to pH level, SO2, and alcohol.) Therefore, fungal pectolytic enzymes are often added to white must to break up pectins, decrease the viscosity of the juice, and speed up settling. In red musts, this increases color and tannin extraction. After fermentation, the force of
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
may eventually cause the wine to "fall bright" or clarify naturally, as the larger suspended particles gradually settle to the bottom of the storage vessel. The wine can then be siphoned or "racked" off the compact solids into a new container.T. Stevenson ''"The Sotheby's Wine Encyclopedia"'' pp. 26–7 Dorling Kindersley 2005 . But this process may take many months, or even years, as well as several rackings, in order to produce a perfectly clear wine. Producers can accelerate the process by using fining agents, filtration and/or flotation.


Fining

In winemaking, fining is the process where a substance (fining agent) is added to the wine to create an adsorbent, enzymatic or
ionic bond Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds ...
with the suspended particles, producing larger molecules and larger particles that will
precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
out of the wine more readily and rapidly. Unlike filtration, which can only remove
particulate Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The te ...
s (such as dead yeast cells and grape fragments), fining can remove soluble substances such as polymerized tannins, coloring
phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...
and
proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
; some of these proteins can cause haziness in wines exposed to high temperatures after bottling. The reduction of tannin can reduce astringency in red wines intended for early drinking.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition pp. 271–72 Oxford University Press 2006 Many substances have historically been used as fining agents, including dried
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
powder A powder is a dry, bulk solid composed of many 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 distin ...
. Today, there are two general types of fining agents — organic compounds and solid/mineral materials.
Organic compounds In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
used as fining agents are generally animal based, a possible cause of concern to
vegans Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. Di ...
.C. Pyevich '
Why is Wine so Fined?
'' Vegetarian Journal, January/February 1997, Volume XVI, Number 1.
The most common organic compounds used include
egg white Egg white is the clear liquid (also called the albumen or the glair/glaire) 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 ar ...
s,
casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins ( αS1, aS2, β, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in hum ...
derived from
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...
,
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
and
isinglass Isinglass () is a substance obtained from the dried swim bladders of fish. It is a form of collagen used mainly for the clarification or fining of some beer and wine. It can also be cooked into a paste for specialised gluing purposes. ...
obtained from the bladders of fish. Pulverized minerals and solid materials can also be used, with
bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...
clay being one of the most common, thanks to its effectiveness in absorbing proteins and some bacteria.
Activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area availa ...
from
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...
is used to remove some phenols that contribute to browning as well as some particles that produce "off-odors" in the wine. In a process known as blue fining,
potassium ferrocyanide Potassium ferrocyanide is the inorganic compound with formula K4 e(CN)6�3H2O. It is the potassium salt of the coordination complex e(CN)6sup>4−. This salt forms lemon-yellow monoclinic crystals. Synthesis In 1752, the French chemist Pie ...
is sometimes used to remove any
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
and
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
particles that have entered the wine from bentonite, metal winery and vineyard equipment, or vineyard sprays such as
Bordeaux mixture Bordeaux mixture (also called ''Bordo Mix'') is a mixture of copper(II) sulphate (CuSO4) and quicklime ( Ca O) used as a fungicide. It is used in vineyards, fruit-farms and gardens to prevent infestations of downy mildew, powdery mildew and othe ...
. Because potassium ferrocyanide may form
hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on a ...
its use is highly regulated and, in many
wine producing countries This list of wine-producing regions catalogues significant growing regions where vineyards are planted. Wine grapes mostly grow between the 30th and the 50th degree of latitude, in both the Northern and Southern hemispheres. Grapes will sometimes ...
, illegal.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition, p. 83 Oxford University Press 2006 .
Silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
and
kaolin Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedra ...
are also sometimes used. Some countries, such as
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
and
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
, have
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. Certain information is ordinarily incl ...
ing laws that require the use of fining agents that may be an allergenic substance to appear on the wine label. A study conducted by the
University of California, Davis Department of Viticulture and Enology The Department of Viticulture and Enology at the University of California, Davis, located in Davis, California, offers undergraduate and graduate degrees in the areas of grape growing and wine making. Located just 45 minutes from Napa Wine Countr ...
, however, found that no detectable amount of inorganic fining agents, and only trace quantities of proteinaceous agents, are left in the wine. There is the risk of valuable aromatic molecules being precipitated out along with the less desirable matter.K. MacNeil ''The Wine Bible'' pp. 35–40 Workman Publishing 2001 . Some producers of premium wine avoid fining, or delay it in order to leach more flavor and
aroma An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sens ...
from the phenols before they are removed.


Filtration

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 larger than the medium's holes. Complete filtration may require a series of filtering through progressively finer filters. Many white wines require the removal of all potentially active yeast and/or
lactic acid bacteria Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped ( bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...
if they are to remain reliably stable in bottle, and this is usually now achieved by fine filtration. Most filtration in a winery can be classified as either the coarser depth filtration or the finer surface filtration. In depth filtration, often done after fermentation, the wine is pushed through a thick layer of pads made from
cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...
fibers,
diatomaceous earth Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to l ...
, or
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. It is an industrial ...
. In surface filtration, the wine passes through a thin membrane. Running the wine
parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster o ...
to the filter surface, known as
cross-flow filtration In chemical engineering, biochemical engineering and protein purification, crossflow filtration (also known as tangential flow filtration) is a type of filtration (a particular unit operation). Crossflow filtration is different from dead-end filtr ...
, will minimize the filter clogging. The finest surface filtration,
microfiltration Microfiltration is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane filter to separate microorganisms and suspended particles from process liquid. It is commonly used in conjunction ...
, can sterilize the wine by trapping all yeast and, optionally, bacteria, and so is often done immediately prior to bottling. An absolute rated filter of 0.45 
µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...
is generally considered to result in a microbially stable wine and is accomplished by the use of membrane cartridges, most commonly
polyvinylidene fluoride Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. PVDF is a specialty plastic used in applications requiring the highest pur ...
(PVDF). Certain red wines may be filtered to 0.65 µm, to remove yeast, or to 1.0 µm to remove viable brettanomyces only.


Flotation

The winemaking technique of flotation was adapted from the
froth flotation Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, wher ...
process used in the
mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the econom ...
industry for ore
refining {{Unreferenced, date=December 2009 Refining (also perhaps called by the mathematical term affining) is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, b ...
. In this process, small bubbles of air (or compressed
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
) are injected into the bottom of a tank. As the bubbles rise through the must, grape solids, including phenolic compounds prone to
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
and browning, will tend to cling to the bubbles, creating a froth that can be removed from the wine. This must be done prior to fermentation, since yeast will inhibit the
flocculation Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from ...
involved.


Stabilization

As a complex chemical mixture dependent on the activity of microorganisms, wine can be
unstable In numerous fields of study, the component of instability within a system is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be mar ...
and reactive to changes in its environment. Once bottled, a wine may be exposed to extremes of
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
and
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...
, as well as violent movement during transportation and storage. These may cause cloudiness, sedimentation and/or the formation of tartrate crystals; more seriously, they may also cause spoilage or the production of
carbonic gas Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is tra ...
.


Temperature instability

Tartaric acid is the most prominent acid in wine with the majority of the concentration present as
potassium bitartrate Potassium bitartrate, also known as potassium hydrogen tartrate, with formula K C4 H5 O6, is a byproduct of winemaking. In cooking, it is known as cream of tartar. It is processed from the potassium acid salt of tartaric acid (a carboxylic ac ...
. During fermentation, these
tartrate A tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. The formula of the tartrate dianion is O−OC-CH(OH)-CH(OH)-COO− or C4H4O62−. The main forms of tartrates used commercially are pure crystalline ta ...
s bind with the lees, pulp debris and precipitated tannins and pigments. While there is some variation according to grape variety and climate, usually about half of the deposits are soluble in the wine, but on exposure to low temperature they may crystallize out unpredictably. The crystals, though harmless, may be mistaken for broken glass, or simply reckoned unattractive by consumers. To prevent this the wine may undergo "cold stabilization", in which it is cooled to near its freezing point to provoke crystallization before bottling.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition, p. 681 Oxford University Press 2006 . In some white wines there are significant quantities of proteins that, being "heat-unstable", will coagulate if exposed to excessively fluctuating heat; the use of fining agents such as bentonite can prevent the haze this causes.


Microbiological instability

A wine that has not been sterilized by filtration might well still contain live yeast cells and bacteria. If both
alcoholic Alcoholism is, broadly, any drinking of alcohol that results in significant mental or physical health problems. Because there is disagreement on the definition of the word ''alcoholism'', it is not a recognized diagnostic entity. Predomina ...
and
malolactic fermentation Malolactic conversion (also known as malolactic fermentation or MLF) is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is most often ...
have run to completion, and neither excessive oxygen nor ''
Brettanomyces ''Brettanomyces'' is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name ''Dekkera'' is used interchangeably with ''Brettanomyces'', as it describes the teleomorp ...
'' yeast are present, this ought to cause no problems; modern
hygiene Hygiene is a series of practices performed to preserve health. According to the World Health Organization (WHO), "Hygiene refers to conditions and practices that help to maintain health and prevent the spread of diseases." Personal hygiene refer ...
has largely eliminated spoilage by bacteria such as acetobacter, which turns wine into
vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to eth ...
. If there is residual sugar, however, it may undergo secondary fermentation, creating dissolved carbon dioxide as a by-product. When the wine is opened, it will be spritzy or " sparkling". In a wine intended to be still this is regarded as a serious fault; it can even cause the bottle to explode. Similarly, a wine that has not been put through complete
malolactic fermentation Malolactic conversion (also known as malolactic fermentation or MLF) is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is most often ...
may undergo it in bottle, reducing its acidity, generating carbon dioxide, and adding a
diacetyl Diacetyl (IUPAC systematic name: butanedione or butane-2,3-dione) is an organic compound with the chemical formula (CH3CO)2. It is a yellow liquid with an intensely buttery flavor. It is a vicinal diketone (two C=O groups, side-by-side). Diacet ...
butterscotch aroma. ''Brettanomyces'' yeasts add
4-ethylphenol Ethylphenol (4-EP) is an organic compound with the formula C2H5C6H4OH. It is one of three isomeric ethylphenols. A white solid, it occurs as an impurity in xylenols and as such is used in the production of some commercial phenolic resins. It is ...
, 4-ethylguaiacol and isovaleric acid horse-sweat aromas. These phenomena may be prevented by sterile filtration, by the addition of relatively large quantities of sulfur dioxide and sometimes
sorbic acid Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula and the structure . It is a colourless solid that is slightly soluble in water and sublimes readily. It was first isol ...
, by mixing in
alcoholic spirit Liquor (or a spirit) is an alcoholic drink produced by distillation of grains, fruits, vegetables, or sugar, that have already gone through alcoholic fermentation. Other terms for liquor include: spirit drink, distilled beverage or ha ...
to give a
fortified wine Fortified wine is a wine to which a distilled spirit, usually brandy, has been added. In the course of some centuries, winemakers have developed many different styles of fortified wine, including port, sherry, madeira, Marsala, Comma ...
of sufficient strength to kill all yeast and bacteria, or by
pasteurization Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life. ...
. Pasteurization gives a
kosher wine Kosher wine () is wine that is produced in accordance with ''halakha'', and more specifically ''kashrut'', such that Jews will be permitted to pronounce blessings over and drink it. This is an important issue, since wine is used in several Jewi ...
of the type called ''mevushal'', literally "cooked" or "boiled", that can be handled by non-Jews and non-observant Jews without losing its
kosher (also or , ) is a set of dietary laws dealing with the foods that Jewish people are permitted to eat and how those foods must be prepared according to Jewish law. Food that may be consumed is deemed kosher ( in English, yi, כּשר), fro ...
status. Typically, the wine is heated to for a minute, then cooled to , at which temperature it remains for up to three days, killing all yeast and bacteria. It may then be allowed to cool, or be bottled "hot" and cooled by water sprays. Since pasteurization affects a wine's flavor and aging potential it is not used for premium wines. A gentler procedure known as
flash pasteurization Flash pasteurization, also called "high-temperature short-time" (HTST) processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, wine, and some dairy products such as milk. Compared with oth ...
involves heating to for a few seconds, followed by rapid cooling.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition p. 508 Oxford University Press 2006


Other methods of stabilization

Clarification tends to stabilize wine, since it removes some of the same particles that promote instability. The gradual
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
that occurs during barrel
aging Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. In ...
also has a naturally stabilizing effect.


Premium wine production

Some producers prefer not to thoroughly clarify and stabilize their wines, believing that the processes involved may diminish a wine's aroma, flavor, texture, color or aging potential. Wine experts such as
Tom Stevenson Tom Stevenson (born 1951) is a British wine writer and critic. Described by his colleagues as one of today's most prolific wine authors, Stevenson is regarded as the world's leading authority on Champagne.christies.coChristie’s Champagne Ma ...
note that they may improve wine quality when used with moderation and care, or diminish it when used to excess. Winemakers deliberately leave more tartrates and phenolics in wines designed for long aging in bottle so that they are able to develop the aromatic compounds that constitute bouquet. The consumers of some wines, such as red
Bordeaux Bordeaux ( , ; Gascon oc, Bordèu ; eu, Bordele; it, Bordò; es, Burdeos) is a port city on the river Garonne in the Gironde department, Southwestern France. It is the capital of the Nouvelle-Aquitaine region, as well as the prefectu ...
and
Port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...
, may expect to see tartrates and sediment after aging in bottle.


References

{{reflist Winemaking Filtration