The chemistry of wine involves a range of chemical compounds and complex processes that shape its production, characteristics, and how it changes over time. This field explores how various molecules interact and evolve, influencing everything from color to aroma and taste.
The Essential Building Blocks
Wine is primarily composed of water, making up 70% to 85% of its volume, derived directly from the grapes. This high water content acts as the main solvent for all other compounds, allowing them to dissolve and interact, contributing to the wine’s overall structure.
Ethanol, or alcohol, is the second most abundant component, ranging from 7% to 15% by volume in fermented wines. It forms during fermentation when yeast consumes the sugars in grape juice, converting them into ethanol and carbon dioxide. Ethanol provides wine with its body, viscosity, and acts as a carrier for many aromatic compounds.
Acids are also present in wine, contributing about 0.5% of its composition, and are measured on a pH scale, between 3 and 4. Organic acids such as tartaric, malic, and citric acids originate from the grapes, while lactic and succinic acids are often formed during fermentation. These acids contribute to freshness, microbiological stability, and influencing the wine’s mouthfeel.
Residual sugars are natural grape sugars that remain after the fermentation process. While dry wines contain very little residual sugar, sweeter wines have higher amounts. These sugars, primarily glucose and fructose, contribute to the wine’s sweetness and can balance its acidity.
Crafting Taste and Aroma
Phenolic compounds are a diverse group found in wine, influencing its color, astringency, and bitterness. Anthocyanins, responsible for the red and purple hues in wine, while tannins contribute to the drying sensation and structure. These compounds are present in higher concentrations in red wines and play a role in their aging potential.
Esters are aromatic compounds formed during fermentation and aging, contributing to fruity, floral, and other complex aromatic notes. These molecules are created through reactions between alcohols and acids, evolving over time to develop different scent profiles.
Terpenes are another class of compounds that give certain grape varieties, like Muscat and Gewürztraminer, their distinctive floral and aromatic profiles. These volatile compounds are present in the grape skins and are released during winemaking, imparting specific aromatic characteristics.
Pyrazines are compounds that contribute vegetal or herbaceous notes, often described as green bell pepper or asparagus, found in wines from grape varieties like Cabernet Sauvignon. These compounds are present in the grapes themselves and contribute to the varietal character of the wine.
Other trace compounds, while present in minute quantities, also contribute to wine’s complex aroma. For instance, lactones can impart buttery or creamy notes, often associated with malolactic fermentation.
Transformations and Influences
Fermentation is a chemical transformation in winemaking, where yeast, converts grape sugars into ethanol and carbon dioxide. This process also yields various byproducts, including glycerol, acetic acid, and succinic acid, which contribute to the wine’s flavor and aroma. Malolactic fermentation involves lactic acid bacteria converting malic acid into softer lactic acid, which can reduce acidity and introduce buttery notes.
Aging, whether in barrels or bottles, introduces further chemical changes that refine wine’s characteristics. Oxidation, a controlled exposure to oxygen, can soften tannins and develop new aromatic compounds, leading to tertiary aromas like dried fruit, tobacco, or leather. Tannins can also polymerize, forming larger molecules that reduce astringency and contribute to mouthfeel over time.
Environmental factors, such as soil composition and climate, influence the chemical makeup of grapes. Soil minerals, temperature, and sunlight exposure affect the ripeness of the grapes and the development of compounds like sugars, acids, and phenolics. For example, warmer climates produce grapes with higher sugar content, leading to wines with higher alcohol levels.
Winemaking interventions also play a chemical role in shaping the final product. Sulfur dioxide (SO2) is frequently used as an antioxidant and antimicrobial agent to prevent spoilage and preserve freshness. Its application helps control undesirable microbial growth and protects the wine from excessive oxidation, maintaining its desired chemical balance.