The Grape & the Vine

Anatomy of the Grape Berry

Every wine begins with a single grape berry, and understanding its parts explains almost everything about how wine gets its color, tannin, and flavor. A ripe wine grape is made up of three basic parts: the skin, the pulp (or flesh), and the seeds, all attached to a woody stem system called the stalk or rachis.

The skin is the outermost layer, and it is where most of a grape's most important winemaking compounds are found:

• Color pigments (anthocyanins) — found only in the skins of black grapes. This is why juice pressed gently from black grapes is pale, and why red wine gets its color from time spent in contact with black grape skins during fermentation.
• Tannins — bitter, mouth-drying compounds concentrated in the skin (and, to a lesser extent, the seeds and stems). Tannins give red wine much of its structure and are far more important in red winemaking than white, because white wines are typically made with little or no skin contact.
• Aroma and flavor compounds — many of a wine's characteristic aromas, especially in naturally aromatic grapes like Muscat and Gewurztraminer, originate in or just beneath the skin.

The pulp, which makes up the bulk of the berry by weight, is mostly juice. It contains:

• Water — typically the largest single component of the pulp.
• Sugars — mainly glucose and fructose, which yeast converts into alcohol and carbon dioxide during fermentation. Sugar level rises as the grape ripens.
• Acids — mainly tartaric and malic acid, which give wine its fresh, tart character and help preserve it. Acid levels fall as the grape ripens.
• A modest amount of flavor compounds, though far less than the skin contributes.

Importantly, the pulp of nearly every grape variety — black or white — is essentially colorless. This is one reason it is possible to make a white-style wine from black grapes: if the juice is pressed off the skins quickly, very little color transfers into it.

The seeds (and the stems, if included) contain harsh, bitter tannins that are generally unwanted in a finished wine. Winemakers try to avoid crushing seeds too aggressively during pressing, and destemming — removing the stalks before fermentation — is common practice specifically to avoid adding this coarse, green tannin to the wine.

What the Vine Needs to Grow

The grapevine used for almost all of the world's wine belongs to a single species, Vitis vinifera. It is a perennial, deciduous, climbing plant that needs several basic inputs to grow, flower, and ripen fruit successfully.

Why Balance Matters

A recurring idea throughout grape growing is balance. A vine needs enough warmth, sunlight, and water to ripen its fruit fully, but not so much that the grapes become overripe, diluted, or the vine unhealthily stressed. The same idea of balance applies within the berry itself: a wine's quality depends on the grape reaching the right balance of sugar, acid, tannin, and flavor at the moment of picking, not simply on ripening as much as possible.

This concept of balance — in the vineyard and ultimately in the glass — underpins nearly every decision a grape grower and winemaker makes. It reappears throughout the rest of this study guide, from the ripening decisions covered next, to the climate and site factors that shape a vineyard's potential, to the winemaking style choices explored in later chapters. Understanding the grape berry's own anatomy is therefore the essential starting point: every later topic, from tannin management in red winemaking to the labelling of "old vine" wines, ultimately traces back to what is happening inside this small, complex fruit.

The Grape Bunch as a Whole

Grapes grow in clusters, or bunches, attached to the vine's shoots by the woody stalk system known as the rachis. Tightly packed bunches hold moisture between berries and are more prone to fungal disease, while looser bunches dry out faster after rain and stay healthier — bunch shape is partly genetic, and it is one reason some varieties are naturally easier to grow in damp climates than others.

Nearly all fine wine comes from a single grape species, Vitis vinifera, native to Europe and western Asia. Thousands of distinct varieties exist within this one species — Cabernet Sauvignon, Chardonnay, and Pinot Noir are all Vitis vinifera, as different from each other as apple varieties are within a single apple species. Every variety covered later in this guide shares the same basic berry anatomy and vine needs described above.