As we stand on the cusp of the harvest season at Zegini’s Winery, the anticipation and excitement are palpable. The vineyards are abuzz with activity, and the grapes are at their peak, ready to be transformed into exquisite wines. But what exactly happens to these grapes as they ripen? Let’s dive into the fascinating chemistry of grape ripening through the eyes of Dimitris, our dedicated wine grower, and explore how climate intricately weaves its influence into this process.
The Journey of Grape Ripening
Grapes undergo a remarkable transformation as they ripen, a process driven by complex chemical changes that are pivotal for producing high-quality wine. According to Dimitris, “Ripening is where the magic begins. It’s when grapes develop the flavors, aromas, and balance that define our wines.”
1. Phenolic Compounds: The Guardians of Flavor and Color
Phenolic compounds are responsible for the color, tannin structure, and flavor complexity in wine. During ripening, the concentration of these compounds increases, particularly in the skins and seeds of red grape varieties. Dimitris explains, “As the grapes ripen, anthocyanins accumulate in the skins, giving red wine its vibrant color. Tannins also evolve, becoming less astringent and more refined, contributing to the wine’s mouthfeel.” The phenolic compounds have a wide variety of structures, divided into flavonoids and non-flavonoids. Among the flavonoids, anthocyanins and flavan-3-ols are particularly important in oenology, as they are respectively the red pigments in grapes and tannins.
A comparison of the phenolic composition of grapes and wine shows that, as well as molecules derived directly from the grape, other polyphenols appear in the wine. During vinification and ageing, polyphenolic compounds take part in various types of reaction. In red wine, the colour constantly evolves during maturation and ageing, gradually changing from a purplish red to a tile-like hue.
2. Sugars: The Sweet Heart of Ripeness
The sweetness of grapes is a direct result of sugar accumulation, primarily glucose and fructose. These sugars are the primary source of fermentable material that yeast will later convert into alcohol. “We monitor Brix levels closely,” Dimitris notes, “which tells us the sugar content of the grapes. The ideal balance of sugars is crucial for achieving the desired alcohol level and sweetness in the wine.”
3. Acid Levels: Striking the Perfect Balance
Acidity plays a key role in the taste profile and preservation of wine. During ripening, the levels of tartaric and malic acids shift. “In the early stages, grapes are high in malic acid, which gives a sharp, green apple-like taste,” says Dimitris. “As they ripen, malic acid decreases, and tartaric acid becomes more prominent, providing a more stable and desirable acidity.”
4. Aroma Precursors: The Birth of Bouquet
The development of aroma compounds, such as terpenes, norisoprenoids, and thiols, is another critical aspect of grape ripening. These compounds are precursors to the aromas and flavors that make each wine unique. “We can already smell the subtle hints of what’s to come in the wine,” Dimitris enthuses. “These aroma precursors are like a sneak peek into the future personality of the wine.”
A couple of examples of these aroma compounds that are only freed and detectable post-fermentation are:
Thiols: Thiols are responsible for the box tree, passion fruit, grapefruit, and gooseberry in Sauvignon Blanc. Volatile thiols are more prevalent in Sauvignon Blanc, but other grape varieties contain trace amounts of thiols, such as Riesling, Colombard, Semillon, and Merlot. These thiols are in two general categories of 4MMP and 3MH.
Terpenes: Terpenes give aromatic, fruity, and floral characteristics to a final wine. Linalool and Geraniol give classic grapey characteristics to different Muscat varieties. Classic descriptors for other terpenes (more than 50 different terpene molecules have been identified) are floral, rose, citrus, coriander, and spicy. Terpenes can also be found in Riesling, Gewürztraminer
The Climate’s Influence
The climate is a powerful force that shapes the ripening process. Each season presents unique challenges and opportunities. Dimitris shares, “This year, we had a warmer spring and a mild summer, which accelerated ripening. Consistent sunshine has been perfect for sugar accumulation, while cooler nights helped preserve acidity.”
However, climate change is introducing more unpredictability. “We’ve seen more extreme weather patterns,” Dimitris reflects. “Late frosts, intense heatwaves, and unexpected rain can all impact the ripening process. It requires constant vigilance and adaptability.”
Join Us in the Vineyard
Understanding the ripening process and the chemical changes in grapes enriches our appreciation for the wine in our glass. It’s a journey from the vineyard to the bottle, where nature and science work in harmony.
At Zegini’s Winery, we invite you to join us in this journey. Visit us during the harvest season to witness the ripening process firsthand, engage with our passionate team, and savor the fruits of our labor. As Dimitris says, “There’s nothing quite like tasting a grape straight from the vine and imagining the wine it will become.”
Stay tuned to our blog for more insights into vine growing, winemaking, and the magic that happens here at Zegini’s Winery. Cheers to the harvest and the wonderful wines to come!
Source :
Vilela, Alice. (2020). Modulating Wine Pleasantness Throughout Wine- Yeast Co-Inoculation or Sequential Inoculation. Fermentation. 6. 22. 10.3390/fermentation6010022.
Cheynier V., Souquet J.M., Fulcrand H., Sarni P., Moutounet M., Stabilisation Tanins - Anthocyanes - Donnees Generales, INRA Montpellier
Write by :
Chrysanthi Zegini
Enologist MSc Enology-Viticulture, ISVV Bordeaux