The first fermentation of all wine takes up to a month but at this stage the wine will be sharp in flavour. A second fermentation os required to convert the acidic flavours of the naturally formed malic acid in the wine to the milder lactic acid. This gives red wines a softer more rounded flavour. Wines designed to be drunk fairly young will undergo this process in large stainless steel tanks. Rosé is also created in this way. More complex red wines which are designed to improve with age will be stored in oak barrels from nine months to more than two years to encourage the fuller flavours to develop. The barrels contribute elements to the final flavour and add tannins to the wine which also affects the flavour and feel of the wine in the mouth. The wine will create murky deposits during this process and this will be filtered out prior to bottling in sterilized bottles.