Winemaking
Winemaking, wine-making, or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. There is evidence that suggests that the earliest wine production took place in Georgia and Iran around 6000 to 5000 B.C. The science of wine and winemaking is known as oenology. A winemaker may also be called a [|vintner]. The growing of grapes is viticulture and there are many varieties of grapes.
Winemaking can be divided into two general categories: still wine production and sparkling wine production. Red wine, white wine, and rosé are the other main categories. Although most wine is made from grapes, it may also be made from other plants. Other similar light alcoholic drinks include mead, made by fermenting honey and water, cider, made by fermenting the juice of apples, and perry, made by fermenting the juice of pears, and kumis, made of fermented mare's milk.
Process
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; at this stage red wine making diverges from white wine making.Red wine is made from the must of red or black grapes and fermentation occurs together with the grape skins, which impart color, flavor and tannins to the wine through the process of maceration. White wine is made by fermenting juice 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, or by blending red wine with white wine. White and rosé wines extract little of the grape tannins contained in the skins. Orange wine is wine made with maceration in the manner of rosé or red wine production, but using white wine grape varieties instead of red.
To start primary fermentation, yeast may be added to the must for red wine, or may occur naturally as ambient yeast on the grapes. For white wine, yeast may be added to the juice. During this fermentation, which often takes between one and two weeks, the yeast converts most of the sugars in the grape juice into ethanol and carbon dioxide.
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 then kept warm and the remaining sugars are converted into alcohol and carbon dioxide.
The next process in the making of red wine is malolactic conversion, a bacterial process that converts "crisp, green apple" malic acid to "soft, creamy" lactic acid, softening the taste of the wine. Red wine is characteristically transferred to white oak barrels to mature for a period of weeks or months; this practice imparts oak aromas and some oak tannins 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 wines to over twenty years for wine of good structure with high levels of acid, tannin or sugar. However, only about 10% of all red and 5% of white wine will taste better after five years than they will after just one year. Depending on the quality of the 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.
Variations on the above procedure exist. With sparkling wines such as Champagne and Methodé Champenoise, an additional, "secondary" fermentation takes place inside the bottle, dissolving trapped carbon dioxide in the wine and creating the characteristic bubbles. Bottles then spend 6 months on a riddling rack before being disgorged to remove any sediment that has accrued. An expedited technique using sealed tanks to contain carbon dioxide is known as the bulk Charmat method. Other sparkling wines, such as prosecco, are fermented using force-carbonation — a faster process that involves using machinery to manually add CO2 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 to remain. This can be done by chilling the wine and adding sulphur and other allowable additives to inhibit yeast activity, or by sterile filtering the wine to remove all yeast and bacteria. In the case of sweet wines, initial sugar concentrations are increased by harvesting late, freezing the grapes to concentrate the sugar, 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, high proof neutral grape spirit is added to arrest the fermentation 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 process produces wastewater, pomace, and lees that require collection, treatment, and disposal or beneficial use.
Synthetic wines are a product that do not use grapes at all. Starting with water and ethanol, a number of additives are included, such as acids, amino acids, sugars, and organic compounds.
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 terroir. Given the sensitivity of grapes to weather patterns, winemaking is affected by climate change.Grapes are usually harvested from the vineyard 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, harvesting extends into May.
The most common species of wine grape is Vitis vinifera, which includes nearly all varieties of European origin.
Harvesting and destemming
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, acid and pH of the grapes. Other considerations include phenological ripeness, berry flavor, tannin development. 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. 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, mechanical harvesting of premium winegrapes is more common because of general labor shortages.
Manual harvesting is the hand-picking of grape clusters from the grapevines. 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.
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, as is done with some German Trockenbeerenauslese, avoids this step altogether with the grapes being individually selected.
Crushing and primary (alcoholic) fermentation
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. 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. 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 to encourage the retention of fruity aromas through partial carbonic maceration.
Most red wines derive their color from grape skins 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. It is possible to produce white wines from red grapes by the fastidious pressing of uncrushed fruit. This minimizes contact between grape juice and skins.
An alternative method to maceration is hot press or thermovinification. In this practice, winemakers heat up the grapes to extract the juice rather than pressing using a pressure method. The temperature and time ranges depending on the grape variety and preferences of the winemaker. In addition to extracting the juice, this method is sometimes referred to as pre-fermentation maceration as it extracts tannins and pigment from the skins. As a result this is applicable to red grape varieties that would otherwise undergo traditional maceration.
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 as well as potassium ions, which participate in bitartrate precipitation. 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 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 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, with the help of a specialized type of hydrometer called a saccharometer. If the sugar content of the grapes is too low to obtain the desired alcohol percentage, sugar can be added. In commercial winemaking, chaptalization is subject to local regulations.
Similar to chaptalization is amelioration. While chaptalization aims to raise final alcohol percentage through the addition of sugar, amelioration aims to raise the alcohol percentage and dilute the acidity levels through the addition of water and sugar into the grape must. This wine adjustment was commonly used in New York State's cooler wine regions, such as the Finger Lakes AVA. Amelioration is also subject to federal 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 can also take place, during which specific strains of bacteria convert malic acid into the milder lactic acid. This fermentation is often initiated by inoculation with desired bacteria.