Wine is fermented grape juice. Yeasts convert the grapes' sugar into alcohol and carbon dioxide, and along the way create hundreds of aroma compounds that give wine its smell and taste.
Three forces shape every finished wine.
The grape
Different varieties carry different potential. A thick skin gives dark colour and more tannin; a thin skin gives pale, elegant wines. How ripe the grape is at harvest sets the balance between sugar and acidity.
The place
Climate, soil and slope affect ripening. A cool climate gives more acidity and lower alcohol. A warm climate gives riper fruit and higher alcohol. That's why a wine from northern France tastes nothing like one from southern Spain.
The people
The winemaker's choices — when to harvest, how warm the fermentation runs, whether the wine ages in oak and how long it rests — decide the style in the glass.
Keep these three in mind and you already have a framework for understanding almost any wine.