Sparkling winemaking covers the processes involved in the manufacture of sparkling wines. The classic Champagne method carries out a second fermentation inside the bottle, building fine, persistent bubbles and complex autolytic flavours during extended ageing on the lees; the tank or Charmat method conducts the secondary fermentation in bulk under pressure, giving fresher, fruitier styles such as prosecco. Direct carbonation by gas injection is the cheapest route but produces coarser, shorter-lived bubbles. Whichever method is used, the wine must be strong enough in bottle and closure to contain several atmospheres of pressure safely.