Along with generating alcohol, the process of fermentation builds gas which is released as bubbles in sparkling wine, once the wine has been opened and poured.
Champagne, Cava, Prosecco
A wine that contains very high levels or sugar is considered a sweet wine, or desert wine. By leaving the grapes on the vine for extended ripening time, the buildup of sugars in the grape continues. Due to the excessive sugar levels achieved, even after fermentation, much of the sugar still remains in the wine.
Gewürztraminer, Riesling, Moscato, Port
If the alcohol content of the wine has been increased by the addition of neutral spirits or bandy it is considered to be fortified.