Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. There are four main methods of sparkling wine production. The first is simple injection of carbon dioxide (CO2), the process used in soft drinks, but this produces big bubbles that dissipate quickly in the glass. The second is the Metodo Italiano - Charmat process, in which the wine undergoes a secondary fermentation in bulk tanks, and is bottled under pressure. This method is used for Prosecco and Asti in particular, and produces smaller, longer-lasting bubbles. This is now used widely around the world to produce light, delicate sparkling wines. The third method is the traditional method or méthode champenoise.[a] With this method the bubbles for more complex wines are produced by secondary fermentation in the bottle.