Understanding How Grapes Used in Wine Vary
Many attributes distinguish each grape variety from the next. The attributes of grape varieties fall into two categories: personality traits and performance factors. Personality traits are the characteristics of the fruit itself — its flavors, for example. Performance factors refer to how the grapevine grows, how its fruit ripens, and how quickly it ripens.
Personality traits of grape varieties
Skin color is the most fundamental distinction among grape varieties. Every grape variety is considered either a white variety or a red (or “black”) one, according to the color of its skins when the grapes are ripe. (A few red-skinned varieties are further distinguished by having red pulp rather than white pulp.)
Individual grape varieties also differ in other ways:
Aromatic compounds: Some grapes (like Muscat) contribute floral aromas and flavors to their wine, for example, while other grapes contribute herbaceous notes (as Sauvignon Blanc does) or fruity character. Some grapes have very neutral aromas and flavors and, therefore, make fairly neutral wines.
Acidity levels: Some grapes are naturally disposed to higher acid levels than others, which influences the wine made from those grapes.
Thickness of skin and size of the individual grapes (called berries): Black grapes with thick skins naturally have more tannin than grapes with thin skins; ditto for small-berried varieties compared to large-berried varieties, because their skin-to-juice ratio is higher. More tannin in the grapes translates into a firmer, more tannic red wine.
The composite personality traits of any grape variety are fairly evident in wines made from that grape. A Cabernet Sauvignon wine is almost always more tannic and slightly lower in alcohol than a comparable Merlot wine, for example, because that’s the nature of those two grapes.
Performance factors of grape varieties
The performance factors that distinguish grape varieties are vitally important to the grape grower because those factors determine how easy or challenging it will be for him to cultivate a specific variety in his vineyard — if he can even grow it at all. The issues include:
How much time a variety typically needs to ripen its grapes. (In regions with short growing seasons, early-ripening varieties do best.)
How dense and compact the bunches of grapes are. (In warm, damp climates, grape varieties with dense bunches can have mildew problems.)
How much vegetation a particular variety tends to grow. (In fertile soils, a vine that’s disposed to growing a lot of leaves and shoots can have so much vegetation that the grapes don’t get enough sun to ripen.)
The reasons some grape varieties perform brilliantly in certain places (and make excellent wine as a result) are so complex that grape growers haven’t figured them all out yet. The amount of heat and cold, the amount of wind and rain (or lack of it), and the slant of the sun’s rays on a hillside of vines are among the factors affecting a vine’s performance. In any case, no two vineyards in the world have precisely the same combination of these factors.