Must Pressing: A Key to Sparkling Wine Quality

Daniella Fracassetti's presentation, "Most Recent Advances in Sparkling Wine Production," delivered at Enoforum, provided a comprehensive overview of one of the most critical phases in sparkling wine production: must pressing. Her discussion honed in on the decision to press either whole clusters or destemmed grapes, highlighting the various factors influencing this choice, including production regulations. Through this analysis, Fracassetti expertly laid out both the benefits and drawbacks of each method, drawing attention to their respective impacts on the final wine's quality and characteristics.

One of the significant advantages of using whole clusters, as explained by Fracassetti, is the role that grape stems (rachis) play as a natural filtration system. This natural filtration helps to clarify the must in the early stages of pressing, a particularly important factor when producing base wines for sparkling wine. Since sparkling wine requires a cleaner must, the clarity gained in the early press fractions directly affects the final product's quality. Fracassetti also emphasized, however, that pressing with the stems introduces the risk of extracting herbaceous or bitter compounds. These potential negatives can be mitigated through careful pressing techniques that limit the extraction of such compounds.

In the initial stages of pressing, Fracassetti noted that the must is typically high in acidity and low in potassium. This balance is critical for sparkling wines, as it ensures stable acidity over time, a key parameter in the winemaking process for this style. She also underscored the importance of suspended solids in the must and how their management could influence the fermentation process and the wine's overall evolution. The presence of solids, while sometimes beneficial for fermentation dynamics, needs to be carefully controlled to avoid adverse effects on flavor and texture.

Fracassetti also touched upon the precise management of sulfur dioxide (SO₂) during the pressing process. Although this compound tends to dissipate early in fermentation, its influence on the solubility and extraction of phenolic compounds cannot be understated. SO₂ plays a vital role in determining the final balance of bitterness and astringency in the wine. In this context, its judicious use is essential to achieving a refined wine profile.

A key focus of Fracassetti's presentation was on phenolic compounds and their critical role in both the stability and sensory profile of sparkling wines. She highlighted that applying lower pressure during pressing reduces the extraction of phenolic compounds, particularly hydroxycinnamic acids and flavonoids. These compounds, while contributing to bitterness and astringency, are also prone to oxidation. Managing the phenolic extraction through controlled pressing thus becomes essential to prevent these undesirable attributes and maintain the wine's stability and sensory appeal.

One of the more innovative aspects of Fracassetti's talk was the mention of the "fingerprinting" technique. This method allows winemakers to obtain a detailed profile of the must during pressing by measuring absorbance at specific wavelengths. This analytical approach offers precise control over the extraction of phenolic compounds, such as hydroxycinnamic acids and anthocyanins. Anthocyanins, responsible for color, can be particularly problematic in sparkling wine production when dealing with varieties like Pinot Noir. Fracassetti warned that increased pressure during pressing could lead to higher anthocyanin extraction, which is undesirable in the production of sparkling wines made from red grape varieties like Pinot Noir when aiming for a clear or pale wine.

Color, as Fracassetti emphasized, serves as an important indicator of must oxidation. She pointed out that monitoring the absorbance at 420 nanometers is essential for evaluating the oxidation state of the must. Higher absorbance at this wavelength correlates with increased oxidation, which tends to occur with more intense pressing. The earliest fractions of must, extracted with the least pressure, generally exhibit lower absorbance values, signaling a fresher, less oxidized state.

Throughout her presentation, Fracassetti made clear that each step of the pressing process is crucial in determining the final quality of sparkling wine. A careful balance of pressing techniques, sulfur dioxide management, and phenolic extraction can significantly influence both the stability and sensory characteristics of the wine. Her detailed insights demonstrated that even minor adjustments in these parameters can lead to meaningful improvements in the quality of sparkling wine, underscoring the complexity and precision required in its production. The presentation at Enoforum 2023 offered valuable knowledge to winemakers looking to refine their practices and optimize the quality of their sparkling wines.