Understanding Phenolic Compounds in Red and White Grapes

The world of wine has long captivated both connoisseurs and enthusiasts alike. Central to this alluring beverage are phenolic compounds, whose study is crucial for understanding the distinctions among various types of wine. These compounds, responsible for characteristics such as color, flavor, and texture, offer a gateway into the art and science of enology.

Phenolic Compounds in Red Grapes

Red grapes contain a variety of phenolic compounds, mainly grouped into two categories: non-flavonoids and flavonoids.

• Non-Flavonoids: Primarily located in the pulp, non-flavonoids include hydroxycinnamic acids (such as caffeic and caftaric) and benzoic acids (like gallic acid). These acids play a pivotal role in shaping the wine's taste profile.
• Flavonoids: Flavonoids, such as flavanols and flavonols, are found in the seeds, skin, and stems. Flavanols, including catechins, significantly contribute to the astringency and structure of the wine. Flavonols, like quercetin and its glucosides, are primarily present in the skin and stems. Additionally, anthocyanins, which give color to the wine, are a type of flavonoid found in the grape skins.

The polymerization of these compounds begins in the grape itself, forming more complex structures like tannins, which are fundamental to the sensory perception of the wine.

Evolution of Phenolic Compounds During Maturation

During the maturation process, tannins and anthocyanins in red grapes undergo significant changes. Following veraison, the stage when the grape changes color, these compounds begin to accumulate, reaching their optimum level at maturity. Subsequently, their levels start to decrease. Interestingly, the tannins from the seeds, although reaching a high level at veraison, become more challenging to extract due to the lignification of the seeds.

Variables Affecting Phenolic Content in Red Grapes

Several factors influence the concentration of phenolic compounds in red grapes:

• The size and number of seeds, as well as the thickness of the skin, can alter the skin-to-pulp ratio, affecting the polyphenolic content.
• Factors such as sampling method, harvest timing, and climatic conditions can impact polyphenol concentration.
• Storage and transportation of samples also influence the extraction and concentration of these compounds.

Measuring Phenolic Compounds in Red Wines

For wine production, it is essential to know the amount of tannins, anthocyanins, and total polyphenols. However, the diversity of methods for measuring these compounds makes it difficult to compare results across different wines. Until an international standard method is established, it is more relevant to observe trends rather than absolute values.

Phenolic Compounds in White Grapes

Unlike red grapes, white grapes do not contain anthocyanins. During the production of white wine, contact with the skins is either nonexistent or limited, so the most relevant phenolic compounds are those present in the pulp, especially non-flavonoids such as hydroxycinnamic acids.

Monitoring Phenolic Parameters in White Wine

In white wine, it is possible to monitor certain phenolic parameters, such as the measure of total polyphenols, the concentration of hydroxycinnamates, and the total concentration of flavonoids.

This analysis of phenolic compounds in red and white grapes offers a deeper understanding of the elements that define each wine's personality. Through this knowledge, producers and oenologists can refine their techniques to create wines that not only delight the palate but also reflect the essence of their terroir.