How White Wines Are Made
There are many styles of white wines, as white wines have many grape varieties. Some of the grape varieties grown in Australia are:
There are many styles of white wines, as white wines have many grape varieties. Some of the grape varieties grown in Australia are:
Each type of wine can be made in a number of different styles. Wines grouped into particular types do not all taste the same, some will smell and taste distinctively of the grapes from which they were made, while others will be more influenced by the winemaking technique or by age.
Wines from the varieties Riesling, Gewurztraminer and Sauvignon Blanc are normally light to medium bodied, having predominant primary fruit aromas and flavours. Wines from the varieties Chardonnay and Semillon are normally medium to full bodied styles and often their character is enhanced by wine making techniques which add complexity, texture and interest.
Harvesting the Grapes
Vintage is the period when the grapes are harvested and the wine is made, this generally occurs between February and May. The decision to remove the grapes from the wine is based on several factors, including:
Harvest commences when the winemaker considers that the grapes have ripened to the right stage for a particular style of wine.
Traditionally grapes have been hand picked into baskets. Hand picking removes whole bunches, leaving the berries attached to their stalks. It also gives minimal berry damage and therefore reduces skin contact and potential oxidation prior to fermentation. While this practice still continues today, many of the larger vineyards are now picked by machines – called mechanical or machine harvested.
Mechanical harvesters operate by moving along the row and shaking the vines. The
movement of the shoots causes the berries to be shaken off their stalks. The berries fall onto a conveyor belt contained in the machine and are carried by the moving belt to a bine for transport to the winery.
Mechanical harvesting has the following advantages:
Mechanical harvesters cannot be used in situations where the vineyard is sited on steep slopes, or where the winemaking technique requires whole bunches of grapes.
Winemaking Process
The major difference between white wine and red wine in terms of processing is that white wine fermentation does not include the contact with the skins. Therefore the juice must be separated first. Listed below are some of the processes.
The grapes are gently crushed. The stalks are removed during this process. The must (juice and skins) is cooled to reduce oxidation and also to get the temperature down for the fermentation process.
Prior to separation from the skins, some skin contact (4-24 hours) may occur dependent upon the grape variety and the winemaker’s philosophy. This is done to extract more varietal character.
In some instances whole bunch pressing will occur, bypassing the crushing process.
After crushing and cooling, the must is extracted from the berries. The greater the pressure the more flavour, colour and tannins will be extracted. Dependent on the quality of the pressings and the style of the wine to be made, the early to mid stage pressings may immediately be blended with the free run.
Prior to fermentation, the juice is generally clarified. Removal of the solids from solution will result in a cleaner fermentation and also assist in controlling the rate of fermentation. The degree of clarification will once again be dependant on winemaker’s philosophy and the style of wine being made.
Clarification is carried out by allowing the juice to stand whilst the smaller solid particles settle to the bottom of the tank. The clear juice is then drawn off into the fermentation vessel. Additional clarification may be conducted by using centrifuges where the solids are removed via centrifugal force, or filtration units.
White wine fermentations are usually carried out at considerably cooler temperatures than red (8-18ºC). This is done to control the fermentation rate so that varietal characters and desirable fermentations characters are retained and reduce off characters, which are produced from “hot” ferments.
In the making of dry white table wines, the fermentation is allowed to continue until all the sugar is fermented to alcohol, with sweet white table wines the fermentation may be stopped part way through. This leaves some fermented unfermented sugar behind which gives the wine its sweet taste.
The fermentation will take place in:
Pure strain yeast are selected according to their ability to ferment under the desired
conditions, produce desirable characters and minimise “off” characters such as hydrogen sulphide.
Wines that rely on varietal aroma (eg Riesling) tend to be fermented completely in stainless steel, clarified and stabilised quickly after fermentation and bottled soon afterwards.
The modern trend with other varieties, such as Chardonnay and Semillon, is to give them full or partial fermentation in oak. These wines may be allowed to have extended lees contact (yeast cells and other precipitates after fermentation) and allowed to undergo malo-lactic fermentation. All of these processes add complexity to the wine. If a wine is to retain some natural residual sugar, fermentation is arrested by lowering the temperature and clarified normally by centrifugation.
Prior to bottling, white wines are generally stabilised to remove unstable proteins and
bitartrate instability. The former is done by using natural clay called bentonite, which
electrostatically combines with the proteins and removes them from solution. The
bitartrates are generally removed by cold stabilisation at temperatures of minus 3ºC.
During the period of time from the end of fermentation to bottling, the winemaker may refine the taste of the wine by adding fining agents such as gelatine and egg white. These fining agents react with and remove phenolic compounds in the wine that would otherwise give overly bitter or course tastes. They also assist in ensuring the wine will be clear, stable and sound.
Bottling
After constantly tasting and assessing the wine, the wine maker will make the decision to bottle the wine. It will be checked for clarity and stability before being filtered into a bottle or cask. Most white wines, particularly sweet white wines, will be sterile filtered which ensures that the wine will be free of any yeast or bacteria that could grow in the wine after bottling. The aim of bottling is to maintain the quality of the wine and also to protect it from oxidisation.
