Only the fortified wines of Oporto can officially use the name. Porto is made by arresting the fermentation of wine (made with up to 80 different varieties) when there is still a high level of residual sugar, adding neutral brandy of wine (fortification), which increases the alcohol level above 18% and then kills the yeast necessary for the fermentation. The Porto resultant is then aged for up to two years before being bottled, where it can continue to age for decades. There are seven main types of Porto: ruby, tawny, vintage, colheita, crusted, late–bottled vintage and white.
