How is Sparkling Wine Produced?
The production of sparkling wines has been well practiced around the world for many years. The most famous of these are the wines of France's Champagnes and Crémants, Italy's Prosecco, and Spain's Cava. Other sparkling wine producing countries include North America, New Zealand, Australia, Germany, Portugal, Hungary, Russia, South Africa, and Romania.
The styles of these wines are very different from each other, not solely because of the grapes used, but also owing to the methods of their production. The grapes used obviously play a big role in the flavour and aroma components of a wine. Like in Champagne, some of the best examples of English sparkling wine use Chardonnay, Pinot noir and Pinot meunier. Some producers use varieties that have been well established as growing well in the UK, such as Seyval blanc, Reichensteiner and even Gamay.
In the production of Cava in Spain, in the North East region of Penedes, traditionally, the indigenous varieties of Macabeo, Xarel-lo and Parellada have been used, but more and more frequently, the classic international varieties of Champagne wines are being used. Italian Prosecco, which has recently been awarded status as a wine producing region, near the Veneto region. The grapes used in the production of Prosecco are called Glera, but are becoming known as Prosecco as a variety. The production of Prosecco employs the Metodo Italiano or Metodo Charmat-Martinotti, whereby secondary fermentation is carried out in large stainless steel tanks, making the production process somewhat cheaper than bottle fermentation.
Sparkling wines can be created in a number of ways. The first - traditional method - whereby a secondary fermentation is encouraged within the bottle through the addition of sugars and yeast and the subsequent storage on yeast lees (sediment) for a number of years. This method is employed by Champagne houses and is also known as methode Champenoise. Most English sparkling wine is made in this way, in part owing to the fact that the process enables desirable aromas and flavours to develop, balancing the crisp acidity of the base wine.
Other methods include secondary fermentation taking place in stainless steel tanks after having gone through primary fermentation and ageing in bottles, later being moved to bottles (transfer method and Charmat method). Another method is through the carbonation of wine through the addition of carbon dioxide other than from its own fermentation. These methods are used for larger scale production of sparkling wines of lesser quality than traditional method wines. Carbonated wines have much bigger bubbles and are much less uniform in their movements to other sparkling wines.
The grapes used in the production of English sparkling wines will almost always be picked by hand rather than using machines. The reason for this is to ensure that the juice in the grapes remains intact, to limit oxidation potential. The whole bunches are carefully picked and placed into baskets which are delivered to the winery and loaded into a press.
The process of making an English sparkling wine in the traditional method - where the wines go through a bottle fermentation - involves the processing of the whole bunches of grapes (with stalks intact) in a very gentle manner, sometimes through the use of a press known as a Coquard. This is a pneumatic press that goes through cycles pressing the grapes softly to avoid over extraction which can deliver undesired elements of astringency and colour into the juice. There are many different types of press that offer a press programme aimed at gentle extraction.
Once pressed, the juice is fermented in the same manner as a still wine, using yeast to cause a fermentation. In most cases, this occurs in temperature controlled stainless steel tanks. When the fermentation has finished and the wines have been settled and filtered to remove skin and grape particles, the wine is known as the sparkling base. In many wineries, a number of separately fermented base wines require blending to reach the desired combination of characters from each. When the winemaker is happy with the blend, the wines can be bottled. It is at this stage that the wines start their journey to becoming sparkling wines.
This process is known as tirage and involves the mixing of yeast and sugar (liqueur de tirage) into the base wine, sometimes accompanied by fining agents, before bottling and capping with a crown cap (like a beer top). The bottles are then stacked and stored in a cool environment for two or three years. The addition of yeast and sugar to the wine and its sealing causes a secondary fermentation. As yeast converts the sugar in the wine into alcohol, it also produces Carbon dioxide. Once the conversion is complete the yeast dies and becomes a sediment within the bottle.
After the years spent in the bottle the dead yeast cells (lees) in the wine need encouraging to fall to the neck of the bottle. This is known as riddling (rémuage). Traditionally done by hand, using a pupitre (an A-framed stand with holes to hold the bottles by their necks) requires 6-8 weeks of regular turning of the bottles. Alternatively, and less labour intensively, a gyropallet (a cage holding 504 bottles that spins slowly on a nine-day cycle,
gently simulating and expediting reumage) can be used. Following this, the sediment from the secondary fermentation will have settled in the neck of the bottle.
The next step is to remove the sediment from the bottle. By freezing the neck of the bottle in a super-coolant, the removal of a small frozen section in the cap containing the lees is possible. The wine shoots out of the bottle owing to the volatility caused by the presence of pressurised CO2, so this process must be carried out quickly so as to cause minimal wine loss. The bottle is placed back under pressure and topped up with the same wine, along with a dosage of liqueur d'expedition (a base wine mixed with sucrose to give the wine its sweetness - Brut, Demi-sec etc.), and SO2 to protect the wine from oxidation or microbial spoilage.
Once the disgorgement and topping up has taken place, the wine is immediately corked and muzzled, before being laid down for a further period of time (the longer the better, but a minimum of 6 weeks is required to allow the liqueur d'expedition to integrate with the wine). After the period of integration, the bottles can be foiled, labelled, and boxed and are then ready to drink.