Winemaking, or
vinification, is the production of
wineWine is an alcoholic beverage typically made of fermented grape juice. The natural chemical balance of grapes is such that they can ferment without the addition of sugars, acids, enzymes or other nutrients. Wine is produced by fermenting crushed grapes using various types of yeast. Yeast consumes...
, starting with selection of the
grapeA grape is the non-climacteric fruit, botanically a true berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, and grape seed oil...
s or other produce and ending with bottling the finished wine. Although most wine is made from grapes, it may also be made from other fruit or non-toxic plant material. Mead is a wine that is made with honey being the primary ingredient after water.
Winemaking can be divided into two general categories: still wine production (without carbonation) and
sparkling wineSparkling wine is a wine with significant levels of carbon dioxide in it making it fizzy. The carbon dioxide may result from natural fermentation, Sparkling wine is a wine with significant levels of carbon dioxide in it making it fizzy. The carbon dioxide may result from natural fermentation,...
production (with carbonation).
The science of wine and winemaking is known as
oenologyOenology, œnology , or enology is the science and study of all aspects of wine and winemaking except vine-growing and grape-harvesting, which is a subfield called viticulture. “Viticulture & oenology” is a common designation for training programmes and research centres that include both the...
(in American English, enology).
Process
After the harvest, the grapes are crushed and allowed to
fermentThe process of fermentation in wine is the catalyst function that turns grape juice into an alcoholic beverage. During fermentation yeast interact with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide...
. Red wine is made from the
mustMust is freshly pressed fruit juice that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace; it typically makes up 7%–23% of the total weight of the must. Making must is the first step in wine-making...
(pulp) of red or black grapes that undergo fermentation together with the grape skins, while white wine is usually made by fermenting
juiceJuice is a liquid naturally contained in fruit or vegetable tissue. Juice is prepared by mechanically squeezing or macerating fresh fruits or vegetables without the application of heat or solvents. For example, orange juice is the liquid extract of the fruit of the orange tree. Juice may be...
pressed from white grapes, but can also be made from must extracted from red grapes with minimal contact with the grapes' skins.
RoséA rosé wine has some of the color typical of a red wine, but only enough to turn it pink. The pink color can range from a pale orange to a vivid near-purple, depending on the grapes and wine making techniques.-Skin contact:...
wines are 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, but little of the
tanninTannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit or red wine...
s contained in the skins.
During this primary fermentation, which often takes between one and two weeks,
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
converts most of the
sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
s in the grape juice into
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
(alcohol) and carbon dioxide. After the primary fermentation, the liquid is transferred to vessels for the secondary fermentation. Here, the remaining
sugarsThe sugars in wine grapes are what make winemaking possible. During the process of fermentation, sugars are broken down and converted by yeasts into ethanol alcohol and carbon dioxide. Grapes accumulate sugars as they grow on the grapevine through the translocation of sucrose molecules that are...
are slowly converted into alcohol and the wine becomes clear. Some wines are then allowed to age in oak barrels before bottling, which add extra aromas to the wine, while others are bottled directly. Still others may be aged in stainless steel tanks or glass carboys. The time from harvest to drinking can vary from a few months for
Beaujolais nouveauBeaujolais nouveau is a red wine made from Gamay grapes produced in the Beaujolais region of France. It is the most popular vin de primeur, fermented for just a few weeks then officially released for sale on the third Thursday of November...
wines to over twenty years for top wines. 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 wines such as Champagne, an additional fermentation takes place inside the bottle, trapping carbon dioxide and creating the characteristic bubbles.
Sweet winesThe sweetness of a wine is defined by the level of residual sugar in the fermentation process.Residual sugar is the measure of the amount of sugars that remain unfermented in the finished wine.-History:...
are made by ensuring that some residual sugar remains after fermentation is completed. This can be done by harvesting late (
late harvest wineLate harvest is a term applied to wines 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 naturally dehydrated while on the vine...
), freezing the grapes to concentrate the sugar (
ice wineIce wine 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 a more concentrated grape must to be pressed from the frozen grapes, resulting in a smaller amount of more...
), or adding a substance to kill the remaining yeast before fermentation is completed; for example, high
proofAlcoholic proof is a measure of how much alcohol is contained in an alcoholic beverage. The measure is commonly used in the United States, where it is defined as twice the percentage of alcohol by volume, and has caused some people to question the necessity of dual labeling.The measurement of...
brandyBrandy is a spirit produced by distilling wine, the wine having first been produced by fermenting grapes. Brandy generally contains 36%–60% alcohol by volume and is typically taken as an after-dinner drink...
is added when making
port winePort wine is a Portuguese fortified wine from the Douro Valley in the northern provinces of Portugal. It is typically a sweet red wine, but also comes in dry, semi-dry and white varieties. It is often served as a dessert wine...
. 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 as süssreserve.
The process produces wastewater,
pomacePomace 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. The OED cites the term marc as having the same meaning....
, and
leesLees refers to deposits of dead yeast or residual yeast and other particles that precipitate, or are carried by the action of "fining", to the bottom of a vat of wine after fermentation and aging. The yeast deposits in beer brewing are known as trub...
that require collection, treatment, and disposal or beneficial use.
The grapes
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
terroirTerroir was originally a French term in wine, coffee and tea used to denote the special characteristics that geography bestowed upon particular varieties. Agricultural sites in the same region share similar soil, weather conditions, and farming techniques, which all contribute to the unique...
.
Grapes are usually harvested from the
vineyardA vineyard 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....
in the autumn (fall), in the northern hemisphere from early September until the beginning of November, or the middle of February until the beginning of March in the southern hemisphere. In some cool areas in the southern hemisphere, for example Tasmania, Australia, harvest extends into the month of May.
The most common species of wine grape is
Vitis viniferaFor the town in Australia, see Vinifera, VictoriaVitis vinifera is a species of Vitis, native to the Mediterranean region, central Europe, and southwestern Asia, from Morocco and Spain north to southern Germany and east to northern Iran.It is a liana growing to 35 m tall, with flaky bark...
, which includes nearly all varieties of European origin.
Harvesting and destemming
HarvestIn agriculture, the harvest is the processes of gathering mature crops from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper. The harvest marks the end of the growing season, or the growing cycle for a particular crop, and this is the...
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),
acidThe acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeasts during fermentation and protecting the wine...
(TA or Titratable Acidity as expressed by
tartaric acidTartaric acid is a white crystalline diprotic organic acid. It occurs naturally in many plants, particularly grapes, bananas, and tamarinds, and is one of the main acids found in wine. It is added to other foods to give a sour taste, and is used as an antioxidant. Salts of tartaric acid are known...
equivalents) and
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
of the grapes. Other considerations include phenological ripeness, berry flavor, tannin development (seed colour and taste). Overall disposition of the grapevine and weather forecasts are taken into account.
Mechanical harvesters are large tractors that straddle grapevine
trellisTrellis may refer to:* Trellis Drainage System* Trellis , a structure that supports climbing plants* Trellis , a special kind of graph, often used in coding...
es and, using firm plastic or rubber rods, strike the fruiting zone of the grapevine to dislodge the grapes from the
rachisThe rachis is the main axis of the inflorescence, or spike, of wheat and other cereals, to which the spikelets are attached. It is also the part of the axis that the pinnae are attached to in ferns, the main stem of a compound leaf , or the main axis in compound inflorescences in other...
. 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 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.
Manual harvesting is the hand-picking of grape clusters from the
grapevineVitis is a genus of about 60 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, both for direct consumption of the fruit and for fermentation to produce...
s. In the United States, grapes are traditionally picked into 30 pound boxes, and in many cases these boxes are consolidated into ½ ton bins or two-ton bins for transport 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.
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 and vegetal flavors in the resulting wine. Single berry harvesting, like what is done with some German
TrockenbeerenausleseTrockenbeerenauslese is a German language wine term for an intensely sweet dessert wine-style wine. Trockenbeerenauslese is the highest category in the Prädikatswein category of the Austrian and German wine classifications...
, avoids this step altogether with the grapes being individually selected.
Crushing and primary fermentation
Crushing is the process of gently squeezing the berries and breaking the skins to start to liberate the contents of the berries. Desteming 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 desteming 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 2-
methoxyIn chemistry , methoxy refers to the functional group consisting of a methyl group bound to oxygen. It has the formula:...
-3-isopropylpyrazine which has an aroma reminiscent of green
bell pepperBell pepper is a cultivar group of the species Capsicum annuum. Cultivars of the plant produce fruits in different colors, including red, yellow, green and orange. Bell peppers are sometimes grouped with less pungent pepper varieties as "sweet peppers". Peppers are native to Mexico, Central America...
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 or Syrah, all or part of the grapes might be left uncrushed (called "whole berry") to encourage the retention of fruity aromas through partial
carbonic macerationCarbonic 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 prior to crushing. Conventional alcoholic fermentation involves crushing the grapes to free the juice and pulp from the...
.
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
anthocyaninAnthocyanins are water-soluble vacuolar pigments that may appear red, purple, or blue according to pH. They belong to a parent class of molecules called flavonoids synthesized via the phenylpropanoid pathway; they are odorless and nearly flavorless, contributing to taste as a moderately stringent...
) 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 (
macerationMaceration is the winemaking process where the phenolic materials of the grape— tannins, coloring agents and flavor compounds— are leached from the grape skins, seeds and stems into the must. The term is usually used in reference to wine, but is sometimes used with other drinks, such as...
). 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 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
BentoniteBentonite is an absorbent aluminium phyllosilicate, generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some...
addition) as well as
PotassiumPotassium is the chemical element with the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash...
ions, which participate in bitartrate precipitation (cream of tartar). 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 wine maker was making a white wine.
Yeast is normally already present on the grapes, often visible as a powdery appearance of the grapes. The 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.
During the primary fermentation, the yeast cells feed on the sugars in the must and multiply, producing carbon dioxide gas and
alcoholIn chemistry, an alcohol is any organic compound in which a hydroxyl group is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is C
nH
2n+1OH...
. 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 weightMust weight is a measure of the amount of sugar in grape juice , and hence indicates the amount of alcohol that could be produced if it is all fermented to alcohol, rather than left as residual sugar...
, with the help of a saccharometer. If the sugar content of the grapes is too low to obtain the desired alcohol percentage, sugar can be added (
chaptalizationChaptalization 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...
). In commercial winemaking, chaptalization is subject to local regulations.
During or after the alcoholic fermentation,
malolactic fermentationMalolactic fermentation is a process of a change used in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid.-Use in winemaking:...
can also take place, during which specific strains of bacteria convert
malic acidMalic acid is an organic compound with the formula HO
2CCH
2CHOHCO
2H. This dicarboxylic acid is the active ingredient in many sour or tart foods. Malic acid is found mostly in unripe fruits....
into the milder
lactic acidLactic acid , also known as milk acid, is a chemical compound that plays a role in several biochemical processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of C
3H
6O
3...
. 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. 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 moveable surface and slowly decrease the volume between the two surfaces. Modern presses are able to follow a pressing program which dictates the duration and pressure at each press cycle, usually ramping from 0
BarThe bar is a unit of pressure equal to 100 kilopascals, and rougly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the decibar , centibar , and millibar...
to 2.0 Bar. Sometimes winemakers choose pressures at which they wish to separate the streams of pressed juice, which is called making "press cuts." As the pressure increases on the grape skins so too increase the amount of tannin extracted into the juice, 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 or pulp, whereas tannins are found primarily in the pericarp, or
skinThe skin is the outer covering of the body. In humans, it is the largest organ of the integumentary system made up of multiple layers of mesodermal tissue, and guards the underlying muscles, bones, ligaments and internal organs. Skin of a different nature exists in amphibians, reptiles, birds...
, and
seedA seed , referred to as a kernel in some plants, is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s), pressed juice or wine tends to be lower in acidity with a higher pH than the free-run juice.
Before the advent of modern winemaking, most presses were
basket pressA wine press is a device used to extract juice from crushed grapes during wine making. There are a number of different styles of presses that are used by wine makers but their overall functionality is the same. Each style of press exerts controlled pressure in order to free the juice from the fruit...
es 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, place the top plate in place and begin to lower it until juice began to flow from the wooden slats. As the juice flow decreased to a minimum, the plate was ratcheted down again until a similar flowrate was achieved. This process would continue until the press operator determines that the quality of the pressed juice or wine is below standard, or all liquids have been pressed from the grape skins. Since the early 1990s, modern mechanical basket presses have seen a resurgence amongst higher-end producers seeking to replicate the gentle pressing of the historical basket presses. Because basket presses have relatively compact design,
the press cake offers a longer relative pathway through which the juice must 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 negatively impact the quality of the press juice.
With red wines, the must is pressed after the 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 its
leesLees refers to deposits of dead yeast or residual yeast and other particles that precipitate, or are carried by the action of "fining", to the bottom of a vat of wine after fermentation and aging. The yeast deposits in beer brewing are known as trub...
), and transferred to a new container where any additional fermentation may take place.
Pigeage
Pigeage is a
FrenchFrench is a Romance language globally spoken by about 65 million people as a first language , by 50 million as a second language, and by about another 200 million people as an acquired foreign language, with significant speakers in 57 countries. Most native speakers of the language live in France,...
winemaking term for the traditional stomping of grapes in open
fermentationFermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. A more restricted definition of fermentation is the chemical conversion of sugars into ethanol...
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 pushed 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
tanninsTannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit or red wine...
, the cap needs to be mixed through the liquid each day, or "punched," which traditionally is done by stomping through the vat.
Cold and heat stabilization
Cold stabilization is a process used in winemaking to reduce
tartrateA tartrate is a salt or ester of the organic compound tartaric acid, a dicarboxylic acid. Its formula is O−OC-CH-CH-COO− or C4H4O62−....
crystals (generally
potassium bitartratePotassium bitartrate, also known as potassium hydrogen tartrate, has formula KC4H5O6. It is a byproduct of winemaking. In cooking it is known as cream of tartar...
) in wine. These tartrate crystals look like grains of clear sand, and are also known as "wine crystals" or "wine diamonds". They may appear to be
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
in the wine, but they are not. During the cold stabilizing process, the temperature of the wine, after fermentation, 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.
During "heat stabilization", unstable proteins are removed by
adsorptionAdsorption is the accumulation of atoms or molecules on the surface of a material. This process creates a film of the adsorbate on the adsorbent's surface. It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution...
onto
bentoniteBentonite is an absorbent aluminium phyllosilicate, generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some...
, preventing them from
precipitatingPrecipitation is the formation of a solid in a solution during a chemical reaction. When the reaction occurs, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate...
in the bottled wine.
Secondary fermentation and bulk aging
During the secondary fermentation and aging process, which takes three(3) to six(6) months, the fermentation continues very slowly. The wine is kept under an
airlockThe fermentation lock or airlock is a device used in beer brewing and wine making that allows carbon dioxide released by the beer to escape the fermenter, while not allowing air to enter the fermenter, thus avoiding oxidation....
to protect the wine from oxidation.
ProteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s from the grape are broken down and the remaining yeast cells and other fine particles from the grapes are allowed to settle.
Potassium bitartratePotassium bitartrate, also known as potassium hydrogen tartrate, has formula KC4H5O6. It is a byproduct of winemaking. In cooking it is known as cream of tartar...
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
rackedRacking is the process of siphoning the wine or beer off the lees into a new, clean barrel or in the case of beer off the trub. Racking allows clarification and aids in stabilization. Wine that is allowed to age on the lees often develops "off-tastes". A racking hose or tubing is used and can be...
during this process to remove the
leesLees refers to deposits of dead yeast or residual yeast and other particles that precipitate, or are carried by the action of "fining", to the bottom of a vat of wine after fermentation and aging. The yeast deposits in beer brewing are known as trub...
.
The secondary fermentation usually takes place in either large
stainless steelIn metallurgy, stainless steel, also known as inox steel or inox, is defined as a steel alloy with a minimum of 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as ordinary steel...
vessels with a volume of several cubic meters of wine, or oak barrels, depending on the goals of the winemakers. Unoaked wine is fermented in a barrel made of stainless steel or other material having no influence in 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 their wine; these vessels (sometimes called
demijohns) have a capacity of 4.5 to 54 liters (1.2–14.3 US gallons). 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 fermentationMalolactic fermentation is a process of a change used in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid.-Use in winemaking:...
is carried out by bacteria which metabolize
malic acidMalic acid is an organic compound with the formula HO
2CCH
2CHOHCO
2H. This dicarboxylic acid is the active ingredient in many sour or tart foods. Malic acid is found mostly in unripe fruits....
and produce
lactic acidLactic acid , also known as milk acid, is a chemical compound that plays a role in several biochemical processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of C
3H
6O
3...
and carbon dioxide. The resultant wine is softer in taste and has greater complexity. The process is used in most red wines and is discretionary for white wines.
Laboratory tests
Whether the wine is aging in tanks or barrels, tests are run periodically in a
laboratoryA laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...
to check the status of the wine. Common tests include
°BrixDegrees Brix is a measurement of the dissolved sugar-to-water mass ratio of a liquid. It is measured with a saccharimeter that measures specific gravity of a liquid or more easily with a refractometer. A 25 °Bx solution is 25% , with 25 grams of sugar per 100 grams of solution...
,
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
, titratable acidity, residual sugar, free or available sulfur, total sulfur, volatile acidity and percent alcohol. These tests are often performed throughout the making of the wine as well as prior to bottling. In response to the results, a winemaker can then decide if more sulfur needs to be added or other slight adjustments before it is bottled.
°Brix is a 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 Soluble Solids (TSS) However, sugar is by far the compound in greatest quantity and so for all practical purposes Brix is a measure of sugar level. The level of sugar in the grapes is important not only because it will determine the final alcohol content of the wine, but also because it is an indirect index of grape maturity. Brix (Bx for short) is measured in grams per hundred grams, so 20 Bx means that 100 grams of juice contains 20gm of dissolved compounds. There are other common measures of sugar content of grapes, Specific gravity, Oechsle (Germany) and Beaume (France). The French
BauméThe Baumé scale is a pair of hydrometer scales developed by French pharmacist Antoine Baumé in 1768 to measure density of various liquids. Notated variously as degrees Baume, degrees Baumé; B°, Be°, Bé°, Baume. One scale measures the density of liquids heavier than water and the other, liquids...
(Be° or Bé° for short) has the benefit that one Be° gives approximately one percent alcohol. Also one Be° is equal to 1.8 Brix, that is 1.8 grams of sugar per one hundred grams. This helps with deciding how much
sugar to add if the juice is low in sugar; to achieve one percent alcohol add 1.8 grams per 100 ml or 18 grams per liter. This is the process of chaptalization, legal in some countries illegal in others. However, perfectly acceptable for the home winemaker.
Generally, for the making of dry table wines a Bx of between 20 and 25 is desirable, this is equivalent to Be° of 11 to 14.
A Brix test can be ran either in the lab or out in field for a quick reference number to see what the sugar content is at. Brix is usually measured with a refractometer whilst the other methods use a hydrometer. Generally, hydrometers are a cheaper alternative.
For more accurate use of sugar measurement it should be remembered that all measurements are affected by the temperature at which the reading is made, suppliers of equipment generally will supply correction charts.
Volatile acidity test verifies if there is any steam distillable acids in the wine. Mainly present is acetic acid but lactic, butyric, propionic and formic acids can also be found. Usually the test checks for these acids in a cash still, but there are new methods available such as HPLC, gas chromatography and even enzymatic methods. The amount of volatile acidity found in sound grapes is negligible. It is a by-product of microbial metabolism. It's important to remember that acetic acid bacteria require oxygen to grow. Eliminating any air in wine containers as well as a sulfur dioxide addition will limit their growth. Rejecting moldy grapes will also prevent 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.
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, 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).
GelatinGelatin is a translucent, colorless, odorless, brittle, nearly tasteless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning...
has been used in winemaking for centuries and is recognized as a traditional method for wine fining, or clarifying. Generally no gelatin remains in the wine because it reacts with the wine components, as it clarifies, and forms a
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
which is removed by filtration prior to bottling.
Besides gelatin, other fining agents for wine are often derived from animal and fish products, such as micronized potassium casseinate (
caseinCasein is the predominant phosphoprotein that accounts for nearly 80% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins, K-Casein, thus originating an unstable micellar state that results in clot formation. When coagulated with rennin, casein is...
is milk protein), egg whites, egg
albuminAlbumin refers generally to any protein with water solubility, which is moderately soluble in concentrated salt solutions, and experiences heat coagulation...
,
bone charBone char, also known as bone black, ivory black, animal charcoal, or abaiser, is a granular material produced by charring animal bones: the bones are heated to high temperatures in an oxygen-depleted atmosphere to control the quality of the product as related to its adsorption capacity for...
,
bullCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
's blood,
isinglassIsinglass is a substance obtained from the swimbladders of fish . It is a form of collagen used mainly for the clarification of wine and beer.-Use in foods and drinks:...
(Sturgeon bladder), PVPP (a dairy derivative protein),
lysozymeLysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, are a family of enzymes which damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine...
, and
skim milk powderPowdered milk is a manufactured dairy product made by evaporating milk to dryness. One purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for...
.
Some aromatized wines contain
honeyHoney is a sweet food made by some insects using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans...
or egg-yolk extract.
Non-
animal-basedAnimal products are either produced by an animal or taken from the body of an animal. The term is primarily used in relation to diet, particularly for vegetarians, vegans and those concerned with maintaining a Kosher, Halaal, or raw food diet....
filtering agents are also often used, such as
bentoniteBentonite is an absorbent aluminium phyllosilicate, generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some...
(a volcanic clay-based filter),
diatomaceous earthDiatomaceous earth — also known as DE, TSS, diatomite, diahydro, kieselguhr, kieselgur, brand names include Celatom or celite — is a naturally occurring, soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder, with a particle size extending from less than 1...
,
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
pads, paper filters and membrane filters (thin films of plastic
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
material having uniformly sized holes).
Preservatives
The most common preservative used in winemaking is
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
. Another useful preservative is
potassium sorbatePotassium sorbate is the potassium salt of sorbic acid. Its primary use is as a food preservative . Potassium sorbate is effective in a variety of applications including food, wine, and personal care.-Chemistry:...
.
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 ferment it will have the effect of preventing or stopping
malolactic fermentationMalolactic fermentation is a process of a change used in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid.-Use in winemaking:...
, 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 stabilize color otherwise it is used at the end of malolactic ferment and performs the same functions as in white wine. However, small additions (say 20 mg per liter) should be used to avoid bleaching red pigments and the maintenance level should be about 20 mg per liter. Furthermore, small additions (say 20 mg per liter) may be made to red wine after alcoholic ferment and before malolactic ferment to over come 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
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
, especially for sweet wines in bottle. However, one potential hazard is the metabolism of sorbate to
geraniolGeraniol is a monoterpenoid and an alcohol. It is the primary part of rose oil, palmarosa oil, and citronella oil . It also occurs in small quantities in geranium, lemon, and many other essential oils. It appears as a clear to pale-yellow oil which is insoluble in water, but soluble in most common...
a potent and very unpleasant by-product. 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
filtrationFiltration is a mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
.
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.
The process of clarification is concerned with the removal of particles; those larger than 5–10 micrometers for coarse polishing, particles larger than 1–4 micrometers for clarifying or polishing. Microbial stabilization requires a filtration of at least 0.65 micrometers. However, filtration at this level may lighten a wines color and body. Microbial stabilization does not imply sterility. It simply means that a significant amount of yeast and bacteria have been removed.
Bottling
A final dose of
sulfiteSodium metabisulfite or sodium pyrosulfite is an inorganic compound of chemical formula Na2S2O5. The name is sometimes referred to as disodium...
is added to help preserve the wine and prevent unwanted fermentation in the bottle. The wine bottles then are traditionally sealed with a
corkCork material is an impermeable, buoyant material, a subset of generic cork tissue that is harvested for commercial use primarily from Quercus suber that is endemic to southwest Europe and northwest Africa...
, although
alternative wine closuresAlternative 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 protect against "cork taint" caused by the presence of...
such as synthetic corks and screwcaps, which are less subject to
cork taintCork 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...
, 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.
Winemakers
Traditionally known as a
vintner, a
winemakerA winemaker or vintner is a person engaged in making wine. They are generally employed by wineries or wine companies, where their work includes:*Cooperating with viticulturists...
is a person engaged in making wine. They are generally employed by
wineriesA 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...
or wine companies.
See also
- 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" section below.-A.B.C.:...
- Acids in wine
The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeasts during fermentation and protecting the wine...
- Champagne production
- Governo
Governo is a winemaking technique reportedly invented in Tuscany in 14th century to help complete fermentation and stabilize the wine. The technique involves saving a batch of harvested grape and allowing them to partially dry...
- Sugars in wine
The sugars in wine grapes are what make winemaking possible. During the process of fermentation, sugars are broken down and converted by yeasts into ethanol alcohol and carbon dioxide. Grapes accumulate sugars as they grow on the grapevine through the translocation of sucrose molecules that are...
External links