There are two different methods for producing Prosecco which are both based on the principle of introducing enough carbon dioxide to make the wine effervescent. In both cases, this is achieved by a secondary fermentation, either in a large tank (as in the Charmat Method) or in the bottle itself (Metodo Classico).
The Charmat Method (also known as the Italian Method)
This is the most common method of producing Prosecco. Once the grapes have been harvested they are transported to the winery, where specially designed machinery presses the grapes very gently, so that only the free-run juice from the heart of the grape is extracted (100 kilograms of grapes should give no more than 70 litres of wine). This cloudy juice, known as the ‘must’, is then allowed to settle in a stainless-steel tank, where it is kept at a cool 5-10?C for around ten to 12 hours.
Once the cloudy part of the must has settled, natural yeast is added to the clear liquid and the fermentation process begins. The addition of yeast encourages the natural sugars in the grape juice to convert into alcohol. This first stage of the fermentation process usually takes between 15 and 20 days, during which the tank is kept at a constant temperature of 18-20?C.
The base wine produced in this first stage is then blended with other types of wine before being submitted to a second phase, known as the prise de mousse. It is during this phase that the still wine is transformed into a sparkling wine. After being carefully blended and tasted, the still wine is introduced into pressurised, stainless-steel tanks, along with yeast and sugar, which stimulate the production of bubbles of carbon dioxide in the wine. As soon as the wine has reached the desired alcohol level, it is cooled and filtered, and all of the yeast used in the fermentation process is removed. Some of the residual sugar is kept to give it a bit of sweetness, and finally the Prosecco is bottled under pressure, to ensure that it keeps its bubbles. This part of the production process tends to take around 30 days.
The Metodo Classico (also known as the Traditional Method or Méthode Champenoise)
This is the traditional way of producing sparkling wine, and is much more time- and labour-intensive than the Charmat Method. For this reason, the Traditional Method is less common these days, although it is still the preferred technique for producing champagne in France.
The first phase of the production process is identical to that of the Charmat Method: the grapes are picked and pressed, and yeast is added to the free-run juice once it has settled, to kick-start the fermentation process. The real difference between the two methods is in the second phase of the fermentation process, when the still wine is transformed into a sparkling wine. With the Traditional Method, this phase is completed in the bottle, rather than in a large, pressurised tank. Yeast and sugar are introduced into the bottle of blended still wine, which is then sealed with a crown cap. The bottle is then stored horizontally for several months (or even years, in the case of champagne) as bubbles of carbon dioxide are produced.
The residual yeast must be removed before the sparkling wine is fit for consumption. Every day, for around 10 to 14 days, the bottles are given a slight shake and the storage rack is put at a slightly steeper angle, until eventually the bottles are upside-down. This process is known as riddling, and it allows the residual yeast to gather in the neck of the bottle, which is then frozen so that the plug of ice containing the yeast can be removed. A small dose of sugar is added, and finally the bottles are sealed with corks, labelled, and boxed up in crates.