Evaluating Grape Pomace Cell Walls for Modern Winemaking

A recent study published in the journal Foods highlights grape pomace cell wall material as a promising, sustainable, and allergen-free alternative to traditional wine fining agents.¹ Results show competitive performance in flavanol reduction and comparable turbidity control to conventional methods, with notable effects on color stability. The study controlled key variables using a single wine matrix and outlines future work to assess performance under varying conditions, while addressing scalability challenges such as raw material variability, extraction efficiency, and storage stability.

Part 1 of our interview with José Miguel Hernández Hierro, an associate professor at the Universidad de Sevilla and the lead author of the paper based off this study, focused on how attenuated total reflectance Fourier transform infrared (ATR-FTIR) and principal component analysis (PCA) revealed grape pomace cell wall composition. Part 2 will discuss the scalability challenges in this work, touching upon variables such as raw material variability, extraction efficiency, and storage stability.

How did the fining efficacy of the grape pomace cell wall material compare to conventional agents such as bentonite or egg albumin, particularly in terms of turbidity reduction, color stability, and sensory impact?

To address the comparison with conventional agents, we must distinguish between our findings in a previous study using red grape cell walls and our current research.^1,2

In that earlier work with red grape skins (Tempranillo), we found that cell wall materials are highly competitive, particularly in flavanol reduction, where they achieved reductions of up to 50.87%.² This performance is comparable to, and in some cases surpasses, animal-based proteins like porcine gelatin (33.80% reduction) and is significantly more effective than bentonite (0.02%) or plant proteins like pea and potato.² Regarding turbidity, red grape cell walls showed a reduction between 17% and 27%, performing similarly to bentonite (24.30%), though they were less effective than gelatin (50.25%).² In terms of color stability, these materials showed a higher impact on anthocyanins (roughly 18–22% reduction) compared to traditional proteins, which typically only reduce them by approximately 2%.²

For our current study involving white grape varieties (Zalema, Pedro Ximénez, and Moscatel), we have specifically focused on their ability to reduce flavanols so far, where they have demonstrated significant potential for managing wine astringency.¹ We are currently working on analyzing the remaining parameters, including other families of phenolic compounds, turbidity reduction, color stability for these white grape samples to complete the comparative profile with conventional oenological agents.

Given that one stated advantage is allergen-free fining, what analytical or regulatory criteria were applied to substantiate this claim, especially considering that grape-derived materials may still carry trace proteins of concern to some consumers?

The potential proteins present in the fining material are endogenous to grape processing, because they originate from the skins themselves. This is the key advantage of using grape‑derived pomace as a fining agent: no external or allergenic proteins are introduced into the wine. Unlike animal‑ or cereal‑based fining agents, the material does not add any foreign proteins that could trigger allergen labelling or consumer concern. Instead, it relies on the reuse and valorization of a natural winery by‑product, introducing nothing into the wine that was not already present in the grape at harvest. As a result, the approach supports an allergen‑free, sustainable, and circular fining strategy.

Fining outcomes are known to be sensitive to wine pH, ethanol content, and ionic strength. How did the study account for or control these matrix variables when evaluating the performance of the cell wall material across different red wine compositions?

The sensitivity of fining efficiency to wine pH, ethanol content, and ionic strength is well established, and we acknowledge that these matrix variables can markedly influence the behavior of any clarifying agent. In our study, these factors were controlled by performing all experiments using the same Syrah red wine, which served as a constant model matrix. Consequently, pH, ethanol concentration, ionic strength, and the overall phenolic composition remained unchanged throughout the trials, ensuring that any differences observed in fining performance were attributable solely to the cell‑wall‑derived materials under evaluation.

Looking forward, and in line with the challenges imposed by climate change, which is driving wines toward higher ethanol levels and higher pH, we are planning to extend the study by systematically modifying these parameters in a designed experiment using a model wine. This will allow us to quantify how selected cell‑wall fining agents respond under more extreme and increasingly common compositional scenarios.

Finally, we are also evaluating the fining performance in different red grape varieties, since the phenolic profile, both qualitatively and quantitatively, differs considerably among cultivars. This varietal diversity may influence the interaction mechanisms and, ultimately, the efficiency of the fining process. These complementary studies will help determine the robustness and applicability of grape cell wall materials across a wider range of oenological conditions.

Moving from lab-scale fining trials to industrial application involves challenges around consistency of pomace sourcing, cell wall extraction yield, and shelf life of the fining agent. What steps are planned to address these translational hurdles, and how do you envision integrating this within an existing winery workflow?

The percentage of insoluble cell wall material relative to the total pomace weight varied widely among the selected samples, ranging from 7.44% to 96.82%. Although this evaluation was not included in the present study, it would also be feasible to assess and even predict extraction yield using vibrational spectroscopic techniques (e.g., NIR spectroscopy). Such an approach would enable rapid and non‑destructive screening of pomace batches to identify those offering the most industrially efficient and cost‑effective fining performance, thus supporting process optimization and scalability.

Building on this perspective, we are also currently evaluating the stability of the extracted cell wall material through NIR spectroscopy to determine its suitability for long‑term storage and its robustness as an oenological additive. Although there is still much to be explored, we hope to provide further advances in this area in the near future. We would also like to express our sincere gratitude to our colleagues for their dedication, hard work, and enthusiasm in addressing these new challenges.

The authors would like to thank the Junta de Andalucía for their financial support through project ProyExcel_00602 and the predoctoral contract (USE‑24002‑J) awarded to Julia Gómez Pérez, the doctoral student involved in the project. In addition, the authors acknowledge the support of the Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (CYTED) through the IberbioAl Network (325RT0170).

References

1. Gómez-Pérez, J.; Baca-Bocanegra, B.; Hernández-Hierro, J. M.; et al. White Grape Cell Walls as Fining Agents in Red Wine: Mechanistic Insights from ATR-FTIR Spectroscopy. Foods2026, 15 (6), 1050. DOI: 10.3390/foods15061050
2. Gómez-Pérez, J.; Baca-Bocanegra, B.; González-Miret, M. L.; et al. Development of an Objective Index for Evaluating New Fining Agents Used in Winemaking: A Case Study of the Cell Wall Material from Red Grape Skin. Foods 2025, 14 (21), 3708. DOI: 10.3390/foods14213707