Stems Sweeten Wine: New Research

A recent study by the International Viticulture and Enology Society (IVES) has shed new light on the role of whole cluster winemaking in influencing the sweet flavor profile of wines. The research highlights how the inclusion of stems, known as "escobajos," during fermentation can significantly affect the concentration of astilbin, a phenolic compound that contributes to the perceived sweetness in wines.

The study was conducted across renowned wine regions in France, including Bordeaux, Burgundy, and Beaujolais. These areas were chosen for their diverse grape varieties—Merlot, Gamay, and Pinot Noir—allowing researchers to examine the effects of stem inclusion across different types of grapes. The experiments varied the proportion of stems included in the fermentation process, ranging from 15% to 50% of the total grape clusters, and compared these to wines made with completely destemmed grapes.

Results from the study indicated a noticeable increase in astilbin levels in wines produced with whole clusters. On average, these wines contained 24.3 mg/L of astilbin, compared to 19.7 mg/L in destemmed wines. Given that the taste detection threshold for astilbin is around 5.7 mg/L, these findings suggest that the compound significantly contributes to the sweetness perceived in the final product.

The impact of stem inclusion varied by grape variety. Merlot wines showed an average 36% increase in astilbin concentration when stems were included, while Pinot Noir and Gamay wines exhibited increases of 21% and 12%, respectively. However, in absolute terms, Pinot Noir and Gamay wines had higher astilbin levels than Merlot wines, regardless of winemaking technique.

Further investigation into the distribution of astilbin within the grape cluster revealed that stems and skins are the primary sources of this compound, with minimal amounts present in the pulp and seeds. This distribution pattern varied by grape variety: for Merlot, stems were the predominant source of astilbin, while in Pinot Noir and Gamay, the compound was more evenly distributed between stems and skins.

The study's authors caution that while whole cluster winemaking can enhance the perceived sweetness of wines through increased astilbin levels, it can also introduce other compounds that affect the sensory profile, such as those contributing to bitterness, astringency, or herbal notes. Therefore, they recommend a thoughtful and informed approach to using this technique, balancing the desired and undesired effects on the final wine.

This study underscores the importance of understanding how winemaking practices influence the sensory components of wine. For winemakers, these insights can guide more informed decisions regarding the use of stems during fermentation, ultimately helping to achieve the desired flavor profile and enhance the wine's appeal. As the industry continues to explore the complexities of winemaking, such research provides valuable knowledge that can shape future practices and consumer experiences.

source: https://doi.org/10.20870/oeno-one.2024.58.1.7872