The Choice of Pressing: Whole Grapes or Destemmed Grapes?
In winemaking, the pressing stage plays a crucial role, especially when deciding whether to work with whole or destemmed grapes. This choice can be influenced by several factors, including the production specifications.
Using the whole cluster may have some disadvantages, such as the release of bitter and herbaceous components from the stalk. However, the pressing techniques adopted in the vinification of sparkling wine bases, due to their gentleness, limit the extraction of these undesirable compounds.
In this video extract, taken from the presentation “Most recent advances in sparkling wine production” given by Daniela Fracassetti (University of Milan, Italy) at Enoforum 2023, we analyze how to produce a must for a sparkling wine base.
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The Role of Whole Grapes in Pressing
Utilizing whole grapes during pressing also allows the solid parts of the grape to act as a natural filter. This can influence the turbidity of the different fractions of must collected, ultimately impacting the clarity and quality of the final product.
Focus on Critical Parameters for Sparkling Wine Base Production
Let’s focus on some critical parameters in sparkling wine base production, particularly pH and suspended solids. The must obtained in the early stages of pressing has a higher concentration of acids and a lower concentration of salts, especially potassium. As a result, it is possible to maintain a higher level of acidity over time.
Another essential factor to consider alongside pH is the presence of sulfur dioxide (SO2). Sulfur dioxide tends to dissipate just a few hours after fermentation begins. Adding SO2 can increase the solubility of polyphenols, leading to greater extraction of these compounds. The lower the pressure applied during the pressing phase, the less phenolic content is extracted.
The Importance of Phenolic Compounds
Phenolic compounds play a crucial role in both the stability of the wine and the perception of its volatile components, as well as its bitterness and astringency. When higher pressure is applied during pressing, specific phenolic compounds, particularly hydroxycinnamic acids (such as caffeic acid), catechin, and epicatechin, are more influenced. These compounds are key contributors to the bitterness and astringency, especially in flavonoids, and they also impact stability due to their susceptibility to oxidation.
Advanced Techniques: Phenolic Fingerprinting
To better support producers, a phenolic fingerprinting method has recently been proposed. This technique provides a detailed profile of the must obtained during pressing. As pressure increases, the absorbance at wavelengths of 280-320 nanometers—associated with the presence of phenolic acids and hydroxycinnamic acids—also increases.
In the case of pressing Pinot Noir grapes, as pressure increases, there is also a greater extraction of anthocyanins, which significantly impacts color. This is particularly undesirable in white winemaking using Pinot Noir.
The Role of Color Indices in Wine Oxidation
Color is the primary parameter for assessing the oxidation state of must or wine. By monitoring absorbance at 420 nanometers, it becomes clear that as pressing continues, absorbance increases. The absorbance values at 420 nanometers are notably lower in the first and second pressing fractions, indicating a lower degree of oxidation.
If you want to learn more about this topic on Infowine Premium there is the entire presentation “Most recent advances in sparkling wine production” given by Daniela Fracassetti (University of Milan, Italy) at Enoforum 2023.
