To curb the occurrence of undesirable bacteria and other organisms limiting fermentation sterilize the wort is often sometimes with sulfur dioxide before trial. Fermentation of white wines Most white wines are fermented in stainless steel vats heat controlled. It is a "virgin fermentation", ie without contact with the skins, white must own for producing light wines and very clean. However, currently there are trends that opt for some maceration of the must with the skins, stopping the fermentation by cold treatments (a process called cold maceration). This method gives the wine more body, enhances the sensations in the mouth, increase its aromatic potency, allows a better evolution in the bottle and gives it a longer life to ferment white wines relatively low temperatures of 10 -15 C in order to slow the unfolding of the sugars into alcohol and the release of carbon dioxide, to thereby retain the aromas of wine and, therefore, achieve the highest quality possible ending. Alcoholic fermentation takes place for 10 to 15 days. The fermentation ends when the wine contains between 1 and 2 grams of sugar per liter, at which time it is completely dry, with little presence of sugars. However, there are more poor house white wine is completely dry and usually maintain a certain amount of residual sugar to achieve greater aromatic intensity. Sometimes voluntarily interrupted fermentation in wine alcohol for various reasons, one of the most common is that density has reached the statutory alcohol. In other cases the contrary is activated on a voluntary basis the process of fermentation by the addition of sugary materials, this phenomenon is called chaptalisation and is highly regulated in the wine producing countries.