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Kim Tyrer
 
27 April 2013 | Stories | Kim Tyrer

Wine Making- the Process

Vintage, in wine-making, is the process of picking grapes and creating the finished product. A vintage wine is one made from grapes that were all, or primarily, grown and harvested in a single specified year.

In wine produced on the colder limits of wine production, vintage is often very important, because some seasons will be much warmer and produce riper grapes and better wine for people to drink. On the other hand, a poor growing season can lead to grapes low in sugar, which lowers the quality of the resulting wine.

Wines of superior vintages from prestigious producers and regions will often command much higher prices than those from average vintages. This is especially the case if wines are likely to improve further with some age in the bottle.Some wines are only labeled with a vintage in better-than-average years, to maintain their quality and reputation, while the vast majority of wines are produced to be drunk young and fresh.

Harvest is the picking of the grapes and in many ways the first step in wine production. Grapes are either harvested decision to harvest grapes is typically made by the winemaker and informed by the level of sugar (called Brix),acid(TA as expressed bytartaric acid equivalents) and pH 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.

Destemming is the process of separating stemsfrom the grapes. Depending on the winemaking procedure, this process may beundertaken before crushing with the purpose of lowering the development of tannins and vegetal flavors in the resulting wine. The corkscrew shaped feed augar sits on top of a mechanical crusher/destemmer. Grape clusters are then fed into the machine where they are first crushed, then destemmed. Stems exit at the end while juice, skins, seeds and some debris exit the bottom. Central component of a mechanical destemming. Paddles above the small circular slots rotate to remove the larger chunks of stems. Grapes are pulled off the stems and fall through the holes. Some small amount of stem particles are usually desired to be kept with the grapes for tannin structure.

Winemaking, or vinification, is the production of wine, starting with selection of the grapes or other produce and ending with bottling the finished wine. Although most wine is made from grapes, it may also be made from other fruit or non-toxic plant material. Winemaking can be divided into two general categories: still wine production (without carbonation) and sparkling wine production (with carbonation). The science of wine and winemaking is known as onenogy .

After the harvest, the grapes are crushed and allowed to ferment.Red wine is made from the must(pulp) of red or black grapes that undergo fermentation together with the grape skins, while white wine is usually made by fermenting juice pressed from white grapes, but can also be made from must extracted from red grapes with minimal contact with the grapes' skins. Rose 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 tannins contained in the skins.

 During this primary fermentation, which often takes between one and two weeks, yeast converts most of the sugars in the grape juice into ethanol (alcohol). After the primary fermentation, the liquid is transferred to vessels for the secondary fermentation. Here, the remaining sugars are slowly converted into alcohol and the wine becomes clear. Wine is then allowed to age in oak barrels before bottling, which add extra aromas to the wine, while others are bottled directly. 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 wines are made by ensuring that some residual sugar remains after fermentation is completed. This can be done by harvesting late (late harvest wine), freezing the grapes to concentrate the sugar (ice wine), or adding a substance to kill the remaining yeast before fermentation is completed; for example, high proof brandy is added when making port wine. 

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 large rwineries, 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 . 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 maceration.

Image; Sauvignon Blanc grapes pouring into the crusher at Galafrey Wines.

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 atank 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 sparkling wine, which is derived from Pinot noir, ared 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 grape seeds, 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. 

In the case of rose 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 ifthe 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.

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.

During or after the alcoholic fermentation, malactic 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.

Pressing is the act of applying pressure to grapes or pomacein 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.

Image; pumping grape juice into the 4 tonne bag press.

Image; Basket press at Galafrey Wines for small batches

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 Bar to 2.0 Bar." 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  pulp, whereas tannins are found primarily in the skin,and seeds),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 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, 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 flow rate 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 lees), and transferred to a new container where any additional fermentation may take place.

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 terrior.

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@ 09/02/2017 at 9:12 PM
I read whole article it is just great.I will share it with my friends and family if any student who are not aware about wine making process. It is quite interesting topic I think.

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