Environmental sustainability and the circular economy are gaining importance in agricultural industries globally. Consequently, South Africa Wine dedicates significant resources to funding research projects focused on these critical areas. Additionally, South Africa Wine prioritises the transfer of knowledge and technologies (local and international) related to environmental sustainability and the circular economy to enhance the effective implementation of advancements within the industry.
Yeast lees as yeast nutrients
The art of winemaking is steeped in tradition, yet innovation continues to push the boundaries of what is possible. One of the latest advancements comes from a team of Australian researchers who have turned a common by-product of winemaking, yeast lees, into a valuable resource that can enhance subsequent fermentations. Researchers explored the feasibility of using processed yeast lees generated during alcoholic fermentation as a nutrient supplement in subsequent fermentations. The addition of processed yeast lysates into grape juice was shown to improve fermentation timeframes and influence the production of yeast-derived fermentation volatile compounds in a dose-dependent manner. This study demonstrates that recycling spent lees from winery waste is feasible and provides some strategies for extracting nutrients from winery waste.
The role of nitrogen in fermentation
Nitrogen is a critical nutrient for yeast during the fermentation process. It influences the growth and reproduction of yeast cells and the speed and efficiency of fermentation. Nitrogen is essential, because it supports the synthesis of proteins, nucleic acids and other cellular components within the yeast cells. Without enough nitrogen, yeast cells can become stressed, leading to incomplete fermentation and the production of undesirable compounds that can affect the flavour and aroma of the wine.
Winemakers often supplement grape musts with nitrogen sources to ensure a healthy fermentation process. Common supplements include inorganic nitrogen salts like diammonium phosphate (DAP) and organic nitrogen compounds like yeast cell lysates.
The untapped potential of yeast lees
In addition to producing wine, the fermentation process generates a significant amount of nutrient-rich biomass known as lees. This sediment, which includes dead yeast cells, grape solids and other particulate matter, is typically discarded or used in low-value applications. However, this study explored the potential of recycling yeast lees as a nutrient source for subsequent fermentations.
Yeast lees are rich in nitrogenous compounds, including amino acids and peptides, which are crucial for yeast metabolism. By breaking down the lees, winemakers can recover valuable nutrients that would otherwise go to waste. This offers a sustainable alternative to traditional nitrogen supplements and enhances the winemaking process’s overall efficiency.
Accelerated autolysis and enzymatic lysis
Autolysis is a natural process wherein yeast cells self-destruct, releasing intracellular contents, including nitrogenous compounds. Accelerated autolysis speeds up this process by applying heat or other stress factors. Enzymatic lysis, on the other hand, employs specific enzymes to break down the yeast cell walls more efficiently. Both methods ensure a higher yield of nutrients from the lees, which yeasts can readily assimilate in the subsequent fermentation.
This study assessed three lees treatments: Accelerated autolysis, enzymatic and mechanical lysis. These methods enhanced the lees’ nutrient profile and reduced fermentation times in Chardonnay must. Accelerated autolysis and enzymatic lysis (using Alcalase enzyme) were particularly effective in breaking down yeast cells and releasing nutrients (Table 1).
TABLE 1. Nutrient characterisation of winery yeast lysates. All values are in mg/L. (Reproduced as permitted by the open access policy of Oeno One.)
The benefits of using yeast lees
The reuse of yeast lees as a nutrient supplement offers several advantages:
- Enhanced fermentation efficiency: Treated lees provide a rich source of nutrients that support yeast growth and metabolism, leading to faster and more complete fermentations. This can be particularly beneficial in preventing stuck fermentations, a common challenge in winemaking.
- Improved wine quality: Adding nutrient-rich lees can positively influence the production of yeast-derived volatile compounds, contributing to the wine’s aroma and flavour profile. These compounds include esters, higher alcohols and other metabolites that enhance the wine’s sensory characteristics.
- Sustainability: Recycling lees reduces the need for external nitrogen supplements and minimises waste, aligning with sustainable winemaking practices. By repurposing lees, wineries can lower their environmental impact and promote a more circular economy within the industry.
Challenges and future directions
While the findings are promising, some challenges must be addressed before implementing these methods on a commercial scale. Winery-produced lees can vary significantly in composition and may contain higher levels of grape solids and diverse microbial populations, which could pose a risk of contamination. Further research is needed to optimise the treatment conditions and ensure the microbial safety of the treated lees.
Additionally, the study highlights the need to control the sodium content in treated lees, which can be high due to the treatment process. Adjusting the conditions for accelerated autolysis and enzymatic treatments could help mitigate this issue. High sodium levels can affect the taste of the wine and potentially harm the fermentation process, so careful monitoring and control are essential.
Another aspect to consider is the economic feasibility of these treatments. While the potential benefits are clear, wineries must assess whether the costs of processing the lees outweigh the savings from reduced nitrogen supplement use and improved fermentation performance. Pilot studies and cost-benefit analyses will be crucial in determining the practicality of adopting these methods on a larger scale.
Conclusion
The re-utilisation of wine yeast lees presents a compelling opportunity for the wine industry to enhance fermentation performance and embrace more sustainable practices. By transforming what was once considered waste into a valuable nutrient source, winemakers can improve the efficiency and quality of their products, while reducing their environmental footprint. As research continues to refine these methods, the future of winemaking looks set to benefit from this innovative approach to nutrient recycling.
Reference
Onetto, C., McCarthy, J., Solomon, M., Borneman, A.R. & Schmidt, S.A., 2024. Enhancing fermentation performance through the re-utilisation of wine yeast lees. Oeno One 58(1). https://doi.org/10.20870/oeno-one.2024.58.1.7749.
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