The science of grapes

Grapes, specifically those of the species Vitis vinifera, are among the most significant fruits in global agriculture and commerce. Their importance extends from their role as a staple fresh fruit to their central place in winemaking, an industry with deep cultural and economic roots. The grape berry is often seen as a simple fruit, but scientific analysis reveals a complex structure and chemistry that underpins its value.

A grape berry grows in clusters on the vine. Each cluster is made up of a main stalk, called the peduncle, which branches into smaller stems known as pedicels that hold individual berries. The berries themselves make up the majority of the cluster’s weight. Each berry is divided into three main parts: the skin (exocarp), the pulp (mesocarp), and the seeds.

The skin forms the outer layer and serves as a protective barrier. It is covered by a waxy cuticle that helps prevent water loss and can host wild yeasts important for fermentation. The skin contains few functional stomata, which means grapes are prone to heat stress and splitting after heavy rain. Just beneath the surface, specialized cells synthesize phenolic compounds such as tannins and anthocyanins—pigments responsible for color in red grapes.

The pulp makes up most of the berry’s mass and is composed of large cells filled with water, sugars, and organic acids. This part of the berry is where juice is stored, and it is rich in glucose and fructose, which accumulate during ripening. The balance between these sugars and organic acids like tartaric and malic acid determines the taste profile of both table grapes and wine. The pulp also contains minerals such as potassium, which can influence wine stability.

Seeds are found at the center of the berry. Most grape berries contain one to four seeds, though some varieties are seedless. Seeds are rich in tannins—compounds that contribute bitterness and astringency to wine—and oils high in unsaturated fatty acids like linoleic acid. These seeds also contain proteins and fiber, making them valuable for uses beyond winemaking.

Grape development follows a double sigmoid growth curve with three stages: rapid initial growth after flowering; a lag phase; and then ripening, marked by véraison when berries soften and change color. During ripening, sugar content rises sharply while acidity drops due to dilution and metabolic changes within the berry.

The chemical composition of each part of the grape has direct implications for its use. In winemaking, white wines are typically produced by pressing grapes to separate juice from skins and seeds before fermentation, minimizing extraction of phenolics that could add bitterness or color. Red wines are made by fermenting juice together with skins and seeds to extract color, tannins, and aroma compounds.

The skin is especially important for wine quality because it contains anthocyanins (color pigments), tannins (which affect mouthfeel), flavonols (which stabilize color), and aromatic precursors that contribute to varietal character. Sunlight exposure increases flavonol content but must be managed carefully to avoid sunburn damage.

Seeds are not only important for wine structure but have become valuable in other industries. Grape seed extract (GSE) is produced from seeds left over after winemaking. GSE is rich in proanthocyanidins—powerful antioxidants studied for their potential cardiovascular benefits, including lowering blood pressure and improving blood flow. Grape seed oil, another byproduct, is high in polyunsaturated fats and vitamin E.

The entire solid residue from winemaking—known as pomace—contains skins, seeds, and stems. Once considered waste, pomace is now used as a source of dietary fiber, natural food colorants (from anthocyanins), antioxidants for food preservation, animal feed supplements, and ingredients for cosmetics.

Scientific research continues to explore new uses for grape components. For example, breeding programs aim to develop grape varieties with specific chemical profiles suited to changing climates or enhanced health benefits. As global temperatures rise, understanding how climate affects grape chemistry will be crucial for maintaining wine quality.

In summary, every part of the grape berry—from skin to pulp to seed—plays a distinct role in determining its value for food, beverage, health products, and beyond. Advances in viticulture, enology, and food science continue to unlock new applications for this ancient fruit while addressing modern challenges such as sustainability and climate adaptation.