![Wine grapes baja](https://upload.wikimedia.org/wikipedia/commons/c/c1/Wine_grapes_baja.jpg)
Winemaking or vinification is the production of
wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
, starting with the selection of the
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
, its
fermentation into alcohol, and the bottling of the finished liquid. The
history of wine
Wine has been produced for thousands of years, with evidence of ancient wine production in Georgia from BC (the earliest known traces of wine),
West Azerbaijan province of Iran from BC, Armenia from BC (large-scale production), and Sicil ...
-making stretches over millennia. The science of wine and winemaking is known as
oenology. A
winemaker
A winemaker or vintner is a person engaged in winemaking. They are generally employed by wineries or wine companies, where their work includes:
*Cooperating with viticulturists
*Monitoring the maturity of grapes to ensure their quality and to deter ...
may also be called a vintner. The growing of grapes is
viticulture
Viticulture (from the Latin word for ''vine'') or winegrowing (wine growing) is the cultivation and harvesting of grapes. It is a branch of the science of horticulture. While the native territory of ''Vitis vinifera'', the common grape vine, ran ...
and there are
many varieties of grapes.
Winemaking can be divided into two general categories: still wine production (without carbonation) and
sparkling wine production
Sparkling wine production is the method of winemaking used to produce sparkling wine. The oldest known production of sparkling wine took place in 1531 with the ''ancestral method''.
Pressure and terminology
In popular parlance and also in the ...
(with carbonation – natural or injected).
Red wine
Red wine is a type of wine made from dark-colored grape varieties. The color of the wine can range from intense violet, typical of young wines, through to brick red for mature wines and brown for older red wines. The juice from most purple grap ...
,
white wine
White wine is a wine that is Fermentation in winemaking, fermented without skin contact. The wine color, colour can be straw-yellow, yellow-green, or yellow-gold. It is produced by the alcoholic fermentation of the non-coloured Juice vesicles, ...
, and
rosé are the other main categories. Although most wine is made from
grape
A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters.
The cultivation of grapes began perhaps 8,000 years ago, ...
s, it may also be made from other plants. (See
fruit wine
Fruit wines are fermented alcoholic beverages made from a variety of base ingredients (other than grapes); they may also have additional flavors taken from fruits, flowers, and herbs. This definition is sometimes broadened to include any alcohol ...
.) Other similar light alcoholic drinks (as opposed to
beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
or
spirits
Spirit or spirits may refer to:
Liquor and other volatile liquids
* Spirits, a.k.a. liquor, distilled alcoholic drinks
* Spirit or tincture, an extract of plant or animal material dissolved in ethanol
* Volatile (especially flammable) liquids, ...
) include
mead
Mead () is an alcoholic beverage made by fermenting honey mixed with water, and sometimes with added ingredients such as fruits, spices, grains, or hops. The alcoholic content ranges from about 3.5% ABV to more than 20%. The defining character ...
, made by fermenting
honey
Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
and water,
cider
Cider ( ) is an alcoholic beverage made from the fermented juice of apples. Cider is widely available in the United Kingdom (particularly in the West Country) and the Republic of Ireland. The UK has the world's highest per capita consumption, ...
("apple cider"), made by fermenting the
juice of apples, and
perry
Perry, also known as pear cider, is an alcoholic beverage made from fermented pears, traditionally the perry pear. It has been common for centuries in England, particularly in Gloucestershire, Herefordshire, and Worcestershire. It is also made ...
("pear cider"), made by fermenting the
juice of pears, and
kumis
''Kumis'' (also spelled ''kumiss'' or ''koumiss'' or ''kumys'', see other transliterations and cognate words below under terminology and etymology – otk, airag kk, қымыз, ''qymyz'') mn, айраг, ''ääryg'') is a fermented dairy p ...
, made of fermented mare's milk.
Process
![Wine grape diagram en](https://upload.wikimedia.org/wikipedia/commons/7/70/Wine_grape_diagram_en.svg)
There are five basic stages to the wine making process which begins with harvesting or picking. After the harvest, the grapes are taken into a winery and prepared for primary
ferment
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 ...
. At this stage red wine making diverges from white wine making.
Red wine
Red wine is a type of wine made from dark-colored grape varieties. The color of the wine can range from intense violet, typical of young wines, through to brick red for mature wines and brown for older red wines. The juice from most purple grap ...
is made from 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 t ...
(pulp) of red or black grapes and fermentation occurs together with the grape skins, which give the wine its color.
White wine
White wine is a wine that is Fermentation in winemaking, fermented without skin contact. The wine color, colour can be straw-yellow, yellow-green, or yellow-gold. It is produced by the alcoholic fermentation of the non-coloured Juice vesicles, ...
is made by
fermenting
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 ...
juice
Juice is a drink made from the extraction or Cold-pressed juice, pressing of the natural liquid contained in fruit and vegetables. It can also refer to liquids that are flavored with concentrate or other biological food sources, such as meat ...
which is made by pressing crushed grapes to extract a juice; the skins are removed and play no further role. Occasionally white wine is made from red grapes; this is done by extracting their juice with minimal contact with the grapes' skins.
Rosé wines are either made from red grapes where the juice is allowed to stay in contact with the dark skins long enough to pick up a pinkish color (maceration or saignée), or (less commonly) by blending red wine with white wine. White and rosé wines extract little of the
tannins
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', f ...
contained in the skins.
To start primary fermentation yeast may be added to the must for red wine or may occur naturally as ambient yeast on the grapes or in the air. Yeast may be added to the juice for white wine. During this fermentation, which often takes between one and two weeks, the
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 constitut ...
converts most of the
sugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
s in the grape juice into
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
(alcohol) and carbon dioxide. The carbon dioxide is lost to the atmosphere.
After the primary fermentation of red grapes the
free run wine is pumped off into tanks and the skins are pressed to extract the remaining juice and wine. The press wine is blended with the free run wine at the winemaker's discretion. The wine is kept warm and the remaining
sugars
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
are converted into alcohol and carbon dioxide.
The next process in the making of red wine is malo-lactic conversion. This is a bacterial process which converts "crisp, green apple"
malic acid
Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ...
to "soft, creamy"
lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
softening the taste of the wine. Red wine is sometimes transferred to oak barrels to mature for a period of weeks or months; this practice imparts oak
aromas and some tannin to the wine. The wine must be settled or clarified and adjustments made prior to bottling.
The time from harvest to drinking can vary from a few months for
Beaujolais nouveau
Beaujolais nouveau ( , ) is a red wine made from Gamay grapes produced in the Beaujolais region of France. It is a '' vin de primeur'', fermented for just a few weeks before being released for sale on the third Thursday of November. Distributo ...
wines to over twenty years for wine of good structure with high levels of acid,
tannin
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', ...
or sugar. However, only about 10% of all red and 5% of white wine will taste better after five years than it will after just one year.
[
]
Depending on the quality of grape and the target wine style, some of these steps may be combined or omitted to achieve the particular goals of the winemaker. Many wines of comparable quality are produced using similar but distinctly different approaches to their production; quality is dictated by the attributes of the starting material and not necessarily the steps taken during vinification.
Variations on the above procedure exist. With
sparkling wine
Sparkling wine is a wine with significant levels of carbon dioxide in it, making it fizzy. While the phrase commonly refers to champagne, European Union countries legally reserve that term for products exclusively produced in the Champagne regi ...
s such as
Champagne
Champagne (, ) is a sparkling wine originated and produced in the Champagne wine region of France under the rules of the appellation, that demand specific vineyard practices, sourcing of grapes exclusively from designated places within it, spe ...
and Methodé Champenoise (sparkling wine that is fermented in the style of champagne but is not from the Champagne region of France) an additional, "secondary" fermentation takes place inside the bottle, dissolving trapped carbon dioxide in the wine and creating the characteristic bubbles. Additionally, bottles then spend 6 months on a riddling rack before being disgorged to remove any sediment that has accrued. Other sparkling wines, such as prosecco, are fermented using force-carbonation- a faster process that involves using machinery to manually add CO
2 and create bubbles.
Sweet wines or off-dry wines are made by arresting fermentation before all sugar has been converted into ethanol and allowing some
residual sugar
The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of alcohol, acids, and tannins. Sugars and alcohol enhance a wine's sweetness, whil ...
to remain. This can be done by chilling the wine and adding sulphur and other allowable additives to inhibit yeast activity or sterile filtering the wine to remove all yeast and bacteria. In the case of sweet wines, initial sugar concentrations are increased by harvesting late (
late harvest wine
Late harvest wine is wine made from grapes left on the vine longer than usual. ''Late harvest'' is usually an indication of a sweet dessert wine, such as late harvest Riesling. Late harvest grapes are often more similar to raisins, but have been ...
), freezing the grapes to concentrate the sugar (
ice wine
Ice wine (or icewine; german: Eiswein) is a type of dessert wine produced from grapes that have been frozen while still on the vine. The sugars and other dissolved solids do not freeze, but the water does, allowing for a more concentrated grape ...
), allowing or encouraging ''Botrytis cinerea'' fungus to dehydrate the grapes or allowing the grapes to raisin either on the vine or on racks or straw mats. Often in these high sugar wines, the fermentation stops naturally as the high concentration of sugar and rising concentration of ethanol retard the yeast activity. Similarly in fortified wines, such as
port wine
Port wine (also known as vinho do Porto, , or simply port) is a Portuguese fortified wine produced in the Douro Valley of northern Portugal. It is typically a sweet red wine, often served with dessert, although it also comes in dry, semi- ...
, high
proof neutral grape spirit (
brandy
Brandy is a liquor produced by distilling wine. Brandy generally contains 35–60% alcohol by volume (70–120 US proof) and is typically consumed as an after-dinner digestif. Some brandies are aged in wooden casks. Others are coloured with ...
) is added to arrest the ferment and adjust the alcohol content when the desired sugar level has been reached. In other cases the winemaker may choose to hold back some of the sweet grape juice and add it to the wine after the fermentation is done, a technique known in Germany as
süssreserve
The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of alcohol, acids, and tannins. Sugars and alcohol enhance a wine's sweetness, wh ...
.
The process produces
wastewater
Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...
,
pomace
Pomace ( ), or marc (; from French ''marc'' ), is the solid remains of grapes, olives, or other fruit after pressing for juice or oil. It contains the skins, pulp, seeds, and stems of the fruit.
Grape pomace has traditionally been used to prod ...
, and
lees that require collection, treatment, and disposal or beneficial use.
Synthetic wines, engineered wines or
fake wines, are a product that do not use grapes at all and start with water and ethanol and then adds acids, amino acids, sugars, and organic compounds.
The grapes
![Mthomebrew grapes from harvest](https://upload.wikimedia.org/wikipedia/commons/c/ce/Mthomebrew_grapes_from_harvest.JPG)
The quality of the grapes determines the quality of the wine more than any other factor. Grape quality is affected by variety as well as weather during the growing season, soil minerals and acidity, time of harvest, and pruning method. The combination of these effects is often referred to as the grape's ''
terroir
(, ; from ''terre'', "land") is a French term used to describe the environmental factors that affect a crop's phenotype, including unique environment contexts, farming practices and a crop's specific growth habitat. Collectively, these conte ...
''. Given the sensitivity of grapes to weather patterns,
winemaking is affected by climate change.
Grapes are usually harvested from the
vineyard
A vineyard (; also ) is a plantation of grape-bearing vines, grown mainly for winemaking, but also raisins, table grapes and non-alcoholic grape juice. The science, practice and study of vineyard production is known as viticulture. Vineyards ...
from early September until early November in the northern hemisphere, and mid February until early March in the southern hemisphere. In some cool areas in the southern hemisphere, for example Tasmania, harvesting extends into May.
The most common species of wine grape is
Vitis vinifera
''Vitis vinifera'', the common grape vine, is a species of flowering plant, native to the Mediterranean region, Central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern Iran. There are curre ...
, which includes nearly all varieties of European origin.
Harvesting and destemming
Harvest
Harvesting is the process of gathering a ripe crop from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper. On smaller farms with minimal mechanization, harvesting is the most labor-i ...
is the picking of the grapes and in many ways the first step in wine production. Grapes are either harvested mechanically or by hand. The decision to harvest grapes is typically made by the winemaker and informed by the level of sugar (called
°Brix),
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
(TA or
Titratable Acidity as expressed by
tartaric acid
Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus. Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally i ...
equivalents) and
pH of the grapes. Other considerations include phenological ripeness, berry flavor, tannin development (seed color and taste). Overall disposition of the grapevine and weather forecasts are taken into account.
Mechanical harvesters are large tractors that straddle
grapevine trellises and, using firm plastic or rubber rods, strike the fruiting zone of the grapevine to dislodge the grapes from the
rachis
In biology, a rachis (from the grc, ῥάχις [], "backbone, spine") is a main axis or "shaft".
In zoology and microbiology
In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this c ...
. Mechanical harvesters have the advantage of being able to cover a large area of vineyard land in a relatively short period of time, and with a minimum investment of manpower per harvested ton. A disadvantage of mechanical harvesting is the indiscriminate inclusion of foreign non-grape material in the product, especially leaf stems and leaves, but also, depending on the trellis system and grapevine canopy management, may include moldy grapes, canes, metal debris, rocks and even small animals and bird nests. Some winemakers remove leaves and loose debris from the grapevine before mechanical harvesting to avoid such material being included in the harvested fruit. In the United States mechanical harvesting is seldom used for premium winemaking because of the indiscriminate picking and increased
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 a d ...
of the grape juice. In other countries (such as Australia and New Zealand), mechanical harvesting of premium winegrapes is more common because of general labor shortages.
![Night Harvest of wine grapes](https://upload.wikimedia.org/wikipedia/commons/a/a0/Night_Harvest_of_wine_grapes._Napa%2C_California.JPG)
Manual harvesting is the hand-picking of grape clusters from the
grapevines
''Vitis'' (grapevine) is a genus of 79 accepted species of vining plants in the flowering plant family Vitaceae. The genus is made up of species predominantly from the Northern Hemisphere. It is economically important as the source of grapes, ...
. In the United States, some grapes are picked into one- or two-ton bins for transport back to the winery. Manual harvesting has the advantage of using knowledgeable labor to not only pick the ripe clusters but also to leave behind the clusters that are not ripe or contain
bunch rot or other defects. This can be an effective first line of defense to prevent inferior quality fruit from contaminating a lot or tank of wine.
![Mthomebrew destemmer](https://upload.wikimedia.org/wikipedia/commons/c/c0/Mthomebrew_destemmer.JPG)
Destemming is the process of separating stems from the grapes. Depending on the winemaking procedure, this process may be undertaken before crushing with the purpose of lowering the development of
tannins
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', f ...
and vegetal flavors in the resulting wine. Single berry harvesting, as is done with some German
Trockenbeerenauslese
''Trockenbeerenauslese'' (literal meaning: 'dried berry selection') is a German language wine term for a medium to full body dessert wine.
''Trockenbeerenauslese'' is the highest in sugar content in the ''Prädikatswein'' category of the Austrian ...
, avoids this step altogether with the grapes being individually selected.
Crushing and primary (alcoholic) fermentation
![Mechanical Crusher](https://upload.wikimedia.org/wikipedia/commons/f/f7/Mechanical_Crusher.JPG)
Crushing is the process when gently squeezing the berries and breaking the skins to start to liberate the contents of the berries. Destemming is the process of removing the grapes from the rachis (the stem which holds the grapes). In traditional and smaller-scale wine making, the harvested grapes are sometimes crushed by trampling them barefoot or by the use of inexpensive small scale crushers. These can also destem at the same time. However, in larger wineries, a mechanical crusher/destemmer is used.
The decision about destemming is different for red and white wine making. Generally when making white wine the fruit is only crushed, the stems are then placed in the press with the berries. The presence of stems in the mix facilitates pressing by allowing juice to flow past flattened skins. These accumulate at the edge of the press.
For red winemaking, stems of the grapes are usually removed before fermentation since the stems have a relatively high tannin content; in addition to tannin they can also give the wine a vegetal aroma (due to extraction of
3-isobutyl-2-methoxypyrazine which has an aroma reminiscent of green
bell pepper
The bell pepper (also known as paprika, sweet pepper, pepper, or capsicum ) is the fruit of plants in the Grossum Group of the species ''Capsicum annuum''. Cultivars of the plant produce fruits in different colors, including red, yellow, orange ...
s). On occasion, the winemaker may decide to leave them in if the grapes themselves contain less tannin than desired. This is more acceptable if the stems have 'ripened' and started to turn brown.
If increased skin extraction is desired, a winemaker might choose to crush the grapes after destemming. Removal of stems first means no stem tannin can be extracted. In these cases the grapes pass between two rollers which squeeze the grapes enough to separate the skin and pulp, but not so much as to cause excessive shearing or tearing of the skin tissues. In some cases, notably with "delicate" red varietals such as
Pinot noir
Pinot Noir () is a red-wine grape variety of the species ''Vitis vinifera''. The name may also refer to wines created predominantly from pinot noir grapes. The name is derived from the French language, French words for ''pine'' and ''black.' ...
or
Syrah
Syrah (), also known as Shiraz, is a dark-skinned grape variety grown throughout the world and used primarily to produce red wine. In 1999, Syrah was found to be the offspring of two obscure grapes from southeastern France, Dureza and Mondeuse B ...
, all or part of the grapes might be left uncrushed (called "whole berry") to encourage the retention of fruity aromas through partial
carbonic maceration
Carbonic maceration is a winemaking technique, often associated with the French wine region of Beaujolais, in which whole grapes are fermented in a carbon dioxide rich environment before crushing. Conventional alcoholic fermentation involves cru ...
.
![Mthomebrew crushed grapes](https://upload.wikimedia.org/wikipedia/commons/a/a2/Mthomebrew_crushed_grapes.JPG)
Most red wines derive their color from grape skins (the exception being varieties or hybrids of non-vinifera vines which contain juice pigmented with the dark Malvidin 3,5-diglucoside
anthocyanin
Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
) and therefore contact between the juice and skins is essential for color extraction.
Red wines are produced by destemming and crushing the grapes into a tank and leaving the skins in contact with the juice throughout the fermentation (
maceration). It is possible to produce white (colorless) wines from red grapes by the fastidious pressing of uncrushed fruit. This minimizes contact between grape juice and skins (as in the making of ''
Blanc de noirs
Champagne (, ) is a sparkling wine originated and produced in the Champagne wine region of France under the rules of the appellation, that demand specific vineyard practices, sourcing of grapes exclusively from designated places within it, spe ...
'' sparkling wine, which is derived from Pinot noir, a red vinifera grape).
Most white wines are processed without destemming or crushing and are transferred from picking bins directly to the press. This is to avoid any extraction of tannin from either the skins or grapeseeds, as well as maintaining proper juice flow through a matrix of grape clusters rather than loose berries. In some circumstances winemakers choose to crush white grapes for a short period of skin contact, usually for three to 24 hours. This serves to extract flavor and tannin from the skins (the tannin being extracted to encourage protein precipitation without excessive
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-mon ...
addition) as well as
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
ions, which participate in bitartrate precipitation (
cream of tartar
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 ...
). It also results in an increase in the pH of the juice which may be desirable for overly acidic grapes. This was a practice more common in the 1970s than today, though still practiced by some Sauvignon blanc and Chardonnay producers in California.
In the case of rosé wines, the fruit is crushed and the dark skins are left in contact with the juice just long enough to extract the color that the winemaker desires. The must is then pressed, and fermentation continues as if the winemaker was making a white wine.
Yeast is normally already present on the grapes, often visible as a powdery appearance of the grapes. The primary, or alcoholic fermentation can be done with this natural yeast, but since this can give unpredictable results depending on the exact types of yeast that are present, cultured yeast is often added to the must. One of the main problems with the use of wild ferments is the failure for the fermentation to go to completion, that is some sugar remains unfermented. This can make the wine sweet when a dry wine is desired. Frequently wild ferments lead to the production of unpleasant acetic acid (vinegar) production as a by product.
![Red wine cap](https://upload.wikimedia.org/wikipedia/commons/e/e1/Red_wine_cap.jpg)
During the primary fermentation, the yeast cells feed on the sugars in the must and multiply, producing carbon dioxide gas and
alcohol. The temperature during the fermentation affects both the taste of the end product, as well as the speed of the fermentation. For red wines, the temperature is typically 22 to 25 °C, and for white wines 15 to 18 °C.
For every gram of sugar that is converted, about half a gram of alcohol is produced, so to achieve a 12% alcohol concentration, the must should contain about 24% sugars. The sugar percentage of the must is calculated from the measured density, the
must weight
Must weight is a measure of the amount of sugar in grape juice (must) and, hence, indicates the amount of alcohol that could be produced if it is all fermented to alcohol, rather than left as residual sugar.hydrometer
A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity.
A hydrometer ...
called a
saccharometer
A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity.
A hydrometer ...
. If the sugar content of the grapes is too low to obtain the desired alcohol percentage, sugar can be added (
chaptalization
Chaptalization is the process of adding sugar to unfermented grape must in order to increase the alcohol content after fermentation. The technique is named after its developer, the French chemist Jean-Antoine-Claude Chaptal. This process is not in ...
). In commercial winemaking, chaptalization is subject to local regulations.
Alcohol of more than 12% can be achieved by using yeast that can withstand high alcohol. Some yeasts can produce 18% alcohol in the wine however extra sugar is added to produce a high alcohol content.
During or after the alcoholic fermentation, a secondary, or
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 ...
can also take place, during which specific strains of bacteria (lactobacter) convert
malic acid
Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ...
into the milder
lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
. This fermentation is often initiated by inoculation with desired bacteria.
Pressing
Pressing is the act of applying pressure to grapes or pomace in order to separate juice or wine from grapes and grape skins. Pressing is not always a necessary act in winemaking; if grapes are crushed there is a considerable amount of juice immediately liberated (called free-run juice) that can be used for vinification. Typically this free-run juice is of a higher quality than the press juice. Pressed juice is typically lesser in quality due to the release and increase of total phenolic compounds, as well as browning index and the C6-alcohol levels. These compounds are responsible for the herb-like taste perceived in wine with pressed grapes. However, most wineries do use presses in order to increase their production (gallons) per ton, as pressed juice can represent between 15%-30% of the total juice volume from the grape.
Presses act by positioning the grape skins or whole grape clusters between a rigid surface and a movable surface and slowly decrease the volume between the two surfaces. Modern presses dictate the duration and pressure at each press cycle, usually ramping from 0
Bar
Bar or BAR may refer to:
Food and drink
* Bar (establishment), selling alcoholic beverages
* Candy bar
* Chocolate bar
Science and technology
* Bar (river morphology), a deposit of sediment
* Bar (tropical cyclone), a layer of cloud
* Bar (u ...
to 2.0 Bar. Sometimes winemakers choose pressures which separate the streams of pressed juice, called making "press cuts." As the pressure increases the amount of tannin extracted from the skins into the juice increases, often rendering the pressed juice excessively tannic or harsh. Because of the location of grape juice constituents in the berry (water and acid are found primarily in the
mesocarp
Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Agg ...
or pulp, whereas tannins are found primarily in the
exocarp
Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Aggr ...
, or
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
, and
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s), pressed juice or wine tends to be lower in acidity with a higher pH than the free-run juice.
![Antique Wine Press](https://upload.wikimedia.org/wikipedia/commons/b/b6/Antique_Wine_Press.jpg)
Before the advent of modern winemaking, most presses were
basket presses made of wood and operated manually. Basket presses are composed of a cylinder of wooden slats on top of a fixed plate, with a moveable plate that can be forced downward (usually by a central ratcheting threaded screw). The press operator would load the grapes or pomace into the wooden cylinder, put the top plate in place and lower it until juice flowed from the wooden slats. As the juice flow decreased, the plate was ratcheted down again. This process continued until the press operator determined that the quality of the pressed juice or wine was below standard, or all liquids had been pressed. Since the early 1990s, modern mechanical basket presses have been revived through higher-end producers seeking to replicate the gentle pressing of the historical basket presses. Because basket presses have a relatively compact design, the press cake offers a relatively longer pathway for the juice to travel before leaving the press. It is believed by advocates of basket presses that this relatively long pathway through the grape or pomace cake serves as a filter to solids that would otherwise affect the quality of the press juice.
With red wines, the must is pressed after primary fermentation, which separates the skins and other solid matter from the liquid. With white wine, the liquid is separated from the must before fermentation . With rose, the skins may be kept in contact for a shorter period to give color to the wine, in that case the must may be pressed as well. After a period in which the wine stands or ages, the wine is separated from the dead yeast and any solids that remained (called
lees), and transferred to a new container where any additional fermentation may take place.
Pigeage
Pigeage is a
French term for the management of acidity and secondary pressing of grapes in
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 ...
tanks. To make certain types of wine, grapes are put through a crusher and then poured into open fermentation tanks. Once fermentation begins, the grape skins are
floated to the surface by carbon dioxide gases released in the fermentation process. This layer of skins and other solids is known as the cap. As the skins are the source of the
tannins
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', f ...
, the cap needs to be mixed through the liquid each day, or "punched", which traditionally is done by stomping through the vat.
Cold stabilization
''Cold stabilization'' is a process used in winemaking to reduce
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 ...
crystals (generally
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 ...
) in wine. These tartrate crystals look like grains of clear sand, and are also known as "wine crystals" or "wine diamonds". They are formed by the union of tartaric acid and potassium, and may appear to be
edimentin the wine, though they are not. During the cold stabilizing process after fermentation, the temperature of the wine is dropped to close to freezing for 1–2 weeks. This will cause the crystals to separate from the wine and stick to the sides of the holding vessel. When the wine is drained from the vessels, the tartrates are left behind. They may also form in wine bottles that have been stored under very cold conditions.
Secondary (malolactic) fermentation and bulk aging
![FermentationVessels](https://upload.wikimedia.org/wikipedia/commons/0/02/FermentationVessels.jpg)
During the secondary fermentation and
aging process
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 ...
, which takes three to six months, the fermentation continues very slowly. The wine is kept under an
airlock
An airlock, air-lock or air lock, often abbreviated to just lock, is a compartment with doors which can be sealed against pressure which permits the passage of people and objects between environments of differing pressure or atmospheric compo ...
to protect the wine from oxidation.
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, respo ...
s from the grape are broken down and the remaining yeast cells and other fine particles from the grapes are allowed to settle.
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 ...
will also precipitate, a process which can be enhanced by
cold stabilization to prevent the appearance of (harmless) tartrate crystals after bottling. The result of these processes is that the originally cloudy wine becomes clear. The wine can be
racked
Vox Media, Inc. is an American mass media company based in Washington, D.C., and New York City. The company was established in November 2011 by Jim Bankoff and Trei Brundrett to encompass ''SB Nation'' (a sports blog network founded in 2005 b ...
during this process to remove the
lees.
The secondary fermentation usually takes place in large
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
vessels with a volume of several cubic meters, oak barrels or glass demijohns (also referred to as carboys), depending on the goals of the winemakers. Unoaked wine is fermented in a barrel made of stainless steel or other material having no influence on the final taste of the wine. Depending on the desired taste, it could be fermented mainly in stainless steel to be briefly put in oak, or have the complete fermentation done in stainless steel. Oak could be added as chips used with a non-wooden barrel instead of a fully wooden barrel. This process is mainly used in cheaper wine.
Amateur winemakers often use glass carboys in the production of their wine; these vessels (sometimes called ''demijohns'') have a capacity of . The kind of vessel used depends on the amount of wine that is being made, the grapes being used, and the intentions of the winemaker.
Malolactic fermentation
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 ...
occurs when
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 bacte ...
metabolize
malic acid
Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ...
and produce
lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
and carbon dioxide. This is carried out either as an intentional procedure in which specially cultivated strains of such bacteria are introduced into the maturing wine, or it can happen by chance if uncultivated lactic acid bacteria are present.
Malolactic fermentation can improve the taste of wine that has high levels of malic acid, because malic acid, in higher concentration, generally causes an unpleasant harsh and bitter taste sensation, whereas lactic acid is more gentle and less sour. Lactic acid is an acid found in dairy products. Malolactic fermentation usually results in a reduction in the amount of total acidity of the wine. This is because malic acid has two acid radicals (-COOH) while lactic acid has only one. However, the pH should be monitored and not allowed to rise above a pH of 3.55 for whites or a pH of 3.80 for reds. pH can be reduced roughly at a rate of 0.1 units per 1 gram/litre of tartaric acid addition.
The use of lactic acid bacteria is the reason why some chardonnays can taste "buttery" due to the production of
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 ...
by the bacteria. Most red wines go through complete malolactic fermentation, both to lessen the acid of the wine and to remove the possibility that malolactic fermentation will occur in the bottle.
White wines vary in the use of malolactic fermentation during their making. Lighter aromatic wines such as Riesling, generally do not go through malolactic fermentation. The fuller white wines, such as barrel-fermented chardonnay, are more commonly put through malolactic fermentation. Sometimes a partial fermentation, for example, somewhere less than 50% might be employed.
Laboratory tests
Whether the wine is aging in tanks or barrels, tests are run periodically in a
laboratory
A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physicia ...
to check the status of the wine. Common tests include
Brix,
pH, titratable
acidity
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
,
residual sugar
The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of alcohol, acids, and tannins. Sugars and alcohol enhance a wine's sweetness, whil ...
,
free or available sulfur, total sulfur,
volatile acidity
A wine fault or defect is an unpleasant characteristic of a wine often resulting from poor winemaking practices or storage conditions, and leading to wine spoilage. Many of the compounds that cause wine faults are already naturally present in wine ...
(V.A.) and percent alcohol. Additional tests include those for the crystallization of cream of tartar (
potassium hydrogen tartrate
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 a ...
) and the precipitation of
heat unstable protein; this last test is limited to white wines. These tests may be performed throughout the making of the wine as well as prior to bottling. In response to the results of these tests, a winemaker can decide on appropriate remedial action, for example the addition of more sulfur dioxide. Sensory tests will also be performed and again in response to these a winemaker may take remedial action such as the addition of a protein to soften the taste of the wine.
![Aeration Oxidation apparatus during an AO SO2 test](https://upload.wikimedia.org/wikipedia/commons/1/12/Aeration_Oxidation_apparatus_during_an_AO_SO2_test.jpg)
Brix (°Bx) is one measure of the soluble solids in the grape juice and represents not only the sugars but also includes many other soluble substances such as salts, acids and tannins, sometimes called
total dissolved solids
Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular ( colloidal sol) suspended form. TDS concentrations are often repor ...
(TDS). Because sugar is the dominant compound in grape juice, these units are effectively a measure of sugar level. The level of sugar in the grapes determines the final alcohol content of the wine as well as indirect index of grape maturity. °Bx is measured in grams per hundred grams of solution, so 20 °Bx means that 100 grams of juice contains 20 g of dissolved compounds. There are other common measures of sugar content of grapes,
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
,
Oechsle (Germany) and
Baumé (France). °Bx is usually measured with a refractometer while the other methods use a hydrometer which measures specific gravity. Generally, hydrometers are a cheaper alternative. In the French Baumé (Be° or Bé° for short) one Be° corresponds approximately to one percent alcohol. One Be° is equal to 1.8 °Bx, that is 1.8 grams of sugar per one hundred grams. Therefore, to achieve one percent alcohol the winemaker adds sugar at a rate of 1.8 grams per 100 ml (18 grams per liter) – a practice known as
chaptalization
Chaptalization is the process of adding sugar to unfermented grape must in order to increase the alcohol content after fermentation. The technique is named after its developer, the French chemist Jean-Antoine-Claude Chaptal. This process is not in ...
, which is illegal in some countries and in California.
Volatile acidity test verifies if there is any steam distillable acids in the wine. Mainly present is
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
(the dominant component of
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 et ...
), but
lactic,
butyric,
propionic, and
formic acid
Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Es ...
can also be found. Usually the test checks for these acids in a cash still, but there are other methods available such as HPLC, gas chromatography and enzymatic methods. The amount of volatile acidity found in sound grapes is negligible, because it is a by-product of microbial metabolism. Because acetic acid bacteria require oxygen to grow, eliminating any air in wine containers as well as addition of
sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
(SO
2) will limit their growth. Rejecting moldy grapes also prevents possible problems associated with acetic acid bacteria. Use of sulfur dioxide and inoculation with a low-V.A. producing strain of ''Saccharomyces'' may deter acetic acid producing yeast. A relatively new method for removal of volatile acidity from a wine is reverse osmosis. Blending may also help – a wine with high V.A. can be filtered (to remove the microbe responsible) and blended with a low V.A. wine, so that the acetic acid level is below the sensory threshold.
Sulphur dioxide can be readily measured with relatively simple laboratory equipment. There are several methods available; a typical test involves acidification of a sample with phosphoric acid, distillation of the liberated SO
2, and capture by hydrogen peroxide solution. The SO
2 and peroxide react to form sulphuric acid, which is then titrated with NaOH to an end point with an indicator, and the volume of NaOH required is used to calculate the SO
2 level. This method has inaccuracies associated with red wine, inefficient condensers, and excessive aspiration rate, although the results are reproducible, having an accuracy with just a 2.5–5% error, which is sufficient to control the level of sulphur dioxide in wine.
Blending and fining
Different batches of wine can be mixed before bottling in order to achieve the desired taste. The winemaker can correct perceived inadequacies by mixing wines from different grapes and batches that were produced under different conditions. These adjustments can be as simple as adjusting acid or tannin levels, to as complex as blending different varieties or vintages to achieve a consistent taste.
Fining agents are used during winemaking to remove
tannins
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', f ...
, reduce astringency and remove microscopic particles that could cloud the wines. The winemakers decide on which fining agents are used and these may vary from product to product and even batch to batch (usually depending on the grapes of that particular year).
Gelatin
elatine
''Elatine'' is one of only two genera in the plant family Elatinaceae, the waterwort family. It contains about 25 species of aquatic plants known generally as waterworts. These are annual or perennial plants found in wet areas worldwide.
, Plant ...
has been used in winemaking for centuries and is recognized as a traditional method for wine fining, or
clarifying. It is also the most commonly used agent to reduce the tannin content. Generally no gelatin remains in the wine because it reacts with the wine components, as it clarifies, and forms a
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
which is removed by filtration prior to bottling.
Besides gelatin, other fining agents for wine are often derived from animal products, such as micronized potassium caseinate (
casein
Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins (CSN1S1, αS1, aS2, CSN2, β, K-casein, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of ...
is milk protein),
egg whites, egg
albumin
Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...
,
bone char
Bone char ( lat, carbo animalis) is a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made; however, it consists mainly of tricalcium phosphate (or hydroxyapatite) 57–80%, calci ...
,
bull
A bull is an intact (i.e., not castrated) adult male of the species ''Bos taurus'' (cattle). More muscular and aggressive than the females of the same species (i.e., cows), bulls have long been an important symbol in many religions,
includin ...
's blood,
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.
The ...
(Sturgeon bladder),
PVPP (a synthetic compound),
lysozyme
Lysozyme (EC 3.2.1.17, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside ...
, and
skim milk powder. Although not common, finely ground eggshell is also sometimes used.
Some aromatized wines contain
honey
Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
or egg-yolk extract.
Non-
animal-based filtering agents are also often used, 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-mon ...
(a volcanic clay-based filter),
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 le ...
,
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 wall ...
pads, paper filters and membrane filters (thin films of plastic
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
material having uniformly sized holes).
Preservatives
The most common
preservative
A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...
used in winemaking is
sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
(SO
2), normally added in one of the following forms: liquid sulfur dioxide, sodium or
potassium metabisulphite
Potassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent odour. It is mainly used as an antioxidant or Sterilization (microbiology)#Chemical sterilization, chemical sterilant. As a disulfi ...
. Another useful preservative is
potassium sorbate
Potassium sorbate is the potassium salt of sorbic acid, chemical formula CH3CH=CH−CH=CH−CO2K. It is a white salt that is very soluble in water (58.2% at 20 °C). It is primarily used as a food preservative (E number 202). Potassium so ...
.
Sulfur dioxide has two primary actions, firstly it is an anti microbial agent and secondly an anti oxidant. In the making of white wine it can be added prior to fermentation and immediately after alcoholic fermentation is complete. If added after alcoholic fermentation it will have the effect of preventing or stopping
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 ...
, bacterial spoilage and help protect against the damaging effects of oxygen. Additions of up to 100 mg per liter (of sulfur dioxide) can be added, but the available or free sulfur dioxide should be measured by the aspiration method and adjusted to 30 mg per liter. Available sulfur dioxide should be maintained at this level until bottling. For rose wines smaller additions should be made and the available level should be no more than 30 mg per liter.
In the making of red wine, sulfur dioxide may be used at high levels (100 mg per liter) prior to ferment to assist in color stabilization. Otherwise, it is used at the end of malolactic ferment and performs the same functions as in white wine. However, small additions (say, ) should be used to avoid bleaching red pigments and the maintenance level should be about 20 mg/L. Furthermore, small additions (say 20 mg per liter) may be made to red wine after alcoholic ferment and before malolactic ferment to overcome minor oxidation and prevent the growth of acetic acid bacteria.
Without the use of sulfur dioxide, wines can readily suffer bacterial spoilage no matter how hygienic the winemaking practice.
Potassium sorbate is effective for the control of fungal growth, including
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 constitut ...
, especially for sweet wines in bottle. However, one potential hazard is the metabolism of sorbate to
geraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil, palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in w ...
which is a potent and unpleasant by-product. The production of geraniol occurs only if
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 ...
is present during malo-lactic fermentation. To avoid this, either the wine must be sterile bottled or contain enough sulfur dioxide to inhibit the growth of bacteria. Sterile bottling includes the use of
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 ...
.
Some winemakers practice natural wine making where no preservative is added. Once the wine is bottled and corked, the bottles are put into refrigeration with temperatures near .
Filtration
Filtration in winemaking is used to accomplish two objectives, clarification and microbial stabilization. In clarification, large particles that affect the visual appearance of the wine are removed. In microbial stabilization, organisms that affect the stability of the wine are removed therefore reducing the likelihood of re-fermentation or spoilage.
![Wine labels machine - 20091205](https://upload.wikimedia.org/wikipedia/commons/2/29/Wine_labels_machine_-_20091205.jpg)
The process of clarification is concerned with the removal of particles; those larger than for coarse polishing, particles larger than 1–4 micrometers for clarifying or polishing.
Microbial
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
stabilization requires a filtration of at least 0.65 micrometers for yeast retention and 0.45 µm for bacteria retention. However, filtration at this level may lighten a wine's color and body. Microbial stabilization does not imply
sterility, i.e. eliminating (removing) or killing (deactivating) of all forms of life and other biological agents. It simply means that a significant amount of yeast and bacteria has been removed to a harmless level for the wine stability.
Clarification of the wine can take place naturally by putting the wine into refrigeration at . The wine takes about a month to settle and it is clear. No chemicals are needed.
Bottling
A final dose of
sulfite
Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid ( sulfurous acid) is elusive, its salts are wide ...
is added to help preserve the wine and prevent unwanted fermentation in the bottle. The wine bottles then are traditionally sealed with a
cork
Cork or CORK may refer to:
Materials
* Cork (material), an impermeable buoyant plant product
** Cork (plug), a cylindrical or conical object used to seal a container
***Wine cork
Places Ireland
* Cork (city)
** Metropolitan Cork, also known as G ...
, although
alternative wine closures
Alternative wine closures are substitute closures used in the wine industry for sealing wine bottles in place of traditional cork closures. The emergence of these alternatives has grown in response to quality control efforts by winemakers to p ...
such as synthetic corks and screwcaps, which are less subject to
cork taint
Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening. Though modern studies have sh ...
, are becoming increasingly popular. The final step is adding a capsule to the top of the bottle which is then heated for a tight seal.
Wine bottle closure methods vary greatly considering taste, closure effectiveness, and aesthetic.
Regulation
In the
European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
, each member state is required by Article 146 of
Regulation
Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. For ...
1308/2013 - Establishing a common organisation of the markets in agricultural products and repealing Council Regulations (EEC) No 922/72, (EEC) No 234/79, (EC) No 1037/2001 and (EC) No 1234/2007 - to appoint one or more "competent national authorities" responsible for ensuring compliance with EU rules in the wine sector.
listof these authorities is maintained by the EU.
Winemakers
Traditionally known as a ''vintner'', a
winemaker
A winemaker or vintner is a person engaged in winemaking. They are generally employed by wineries or wine companies, where their work includes:
*Cooperating with viticulturists
*Monitoring the maturity of grapes to ensure their quality and to deter ...
is a person engaged in making wine. They are generally employed by
wineries
A winery is a building or property that produces wine, or a business involved in the production of wine, such as a wine company. Some wine companies own many wineries. Besides wine making equipment, larger wineries may also feature warehouses, b ...
or
wine companies
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are ma ...
, although there are many independent winemakers who make wine at home for their own pleasure or small commercial operation. Additionally, winemaking is still carried in traditional ways by families producing wine for their own consumption.
List of top 15 wine producing countries by volume.
(Volume in thousands of hectoliters)
See also
*
Winery
A winery is a building or property that produces wine, or a business involved in the production of wine, such as a wine company. Some wine companies own many wineries. Besides wine making equipment, larger wineries may also feature warehouses, ...
*
Acids in wine
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Glossary of wine terms
The glossary of wine terms lists the definitions of many general terms used within the wine industry. For terms specific to viticulture, winemaking, grape varieties, and wine tasting, see the topic specific list in the "''#See also, See also''" sec ...
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Governo
Governo is a winemaking technique reportedly invented in Tuscany in the 14th century to help complete fermentation and stabilize the wine. The technique involves saving a batch of harvested grapes and allowing them to partially dry. If fermentat ...
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History of wine
Wine has been produced for thousands of years, with evidence of ancient wine production in Georgia from BC (the earliest known traces of wine),
West Azerbaijan province of Iran from BC, Armenia from BC (large-scale production), and Sicil ...
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Homebrewing
Homebrewing is the brewing of beer or other alcoholic beverages on a small scale for personal, non-commercial purposes. Supplies, such as kits and fermentation tanks, can be purchased locally at specialty stores or online. Beer was brewed dom ...
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List of 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 ...
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Sugars in wine
References
Further reading
* Thomas Pinney. ''The Makers of American Wine: A Record of Two Hundred Years.'' Berkeley. University of California Press, 2012.
*James Simpson. ''Creating Wine: The Emergence of a World Industry, 1840-1914''. Princeton University Press, 2012.
External links
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Fermentation in food processing