Annual Growth Cycle of the Grapevine
Harvest
Depending on the grape variety, region, and wine style, the ripening process can last anywhere from 30 to 70 days after véraison. As for regions, cooler climates, like Germany, typically have longer ripening cycles, while hotter ones, like California’s Central Valley or the Chianti region in Tuscany, Italy (Figure 1.8), have shorter cycles. In general, August, September, and October mark prime time for the annual grape harvest for most wineries in Europe and North America. Australia, New Zealand, South America, and South Africa typically harvest from February to April. Both hemispheres often have harvest extensions on either side of their harvest windows depending on the individual growing season, grape ripeness, and various vintage factors.
Chemical Composition of the Fruit
Berry development includes the accumulation and metabolism of hundreds of compounds, many in tiny quantities, which may contribute to fruit quality attributes. The single largest component of berries is water, followed by the sugars (predominantly fructose and glucose), then the acids tartaric and malic. Other important classes of chemical compounds found in grape berries include sugars, organic acids, potassium levels, phenolic compounds, nitrogenous compounds, and aroma compounds.
Sugars
The majority of soluble solids in grape juice are sugars, mostly glucose and fructose. Sugars increase in concentration during ripening, and may reach 25 percent or more of berry fresh weight by the time of harvest. At veraison, glucose exceeds the fructose concentration but at the ripening stage, glucose and fructose are usually present in equal amounts (1:1 ratio). In overripe grapes, the concentration of fructose exceeds that of glucose.
Organic Acids
Next to sugars, organic acids are the most abundant solids present in grape juice. Acids give crispness, brightness, and thirst-quenching qualities to wines and are essential components of the balance in a fine wine. They have a marked influence on wine stability, color, and pH. Excessive grape acidity can lead to tart, acidic wines.
Phenolic Compounds
Phenolic compounds are often referred to as polyphenolics, polyphenols or simply phenols. Phenolic compounds are important constituents of grapes because they play a key role in determining fruit color and also provide most of the characteristic taste and aging properties in wine.
Nitrogenous Compounds
Grapes contain various nitrogenous compounds such as amino acids, peptides, and proteins. Nitrogen containing compounds are important because they serve as the nutrient for yeast and lactic acid bacteria.
Aroma Compounds
Wine grape aromas come from compound classes like terpenes (floral/citrus in Muscat, Riesling), methoxypyrazines (green bell pepper in Sauvignon Blanc/Cabernet), norisoprenoids (spicy notes in Chardonnay/Syrah), and thiols (passionfruit/gooseberry in Sauvignon Blanc), along with C6 compounds (grassy) and esters (fruity), creating complex aromas from floral and fruit to spicy and vegetal notes, existing in both free and bound forms within the grape. Fermentation creates esters (fruity), higher alcohols, and other volatiles, with aging adding vanillin, lactones, and phenols, all interacting to define a wine’s unique smell and taste profile.
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