Fortified wines are wines that require the addition of alcohol during production. The addition can occur in the must after the pressing of the grapes. In this way fermentation is prevented and sweet fortified wines are produced. In other cases, the addition occurs during fermentation: the moment of addition and the amount of alcohol vary depending on the type of wine, which will be more or less sweet (this is the case of Port). Finally the addition can occur at the end of fermentation, as in Jerez (or Sherry).