Technical Yearbook 2023

Introduction During alcoholic fermentation, wine yeasts produce ethanol, carbon dioxide and several by-products. These by-products include varying concentrations of volatile and aromatic compounds such as higher alcohols, fatty acids, esters and volatile thiols, which contribute significantly to the aromatic composition of the finished wine. The aroma compounds present at the end of fermentation depend primarily on yeast metabolism; however, the concentrations are also significantly modified during fermentation due to losses resulting from volatilisation. A considerable amount of carbon dioxide is produced during alcoholic fermentation. From 100 g of glucose, 51.1 g of ethanol and 48.9 g of carbon dioxide are formed. Some formed carbon dioxide will dissolve into the fermenting must and wine. However, most of the formed carbon dioxide will make its way to the surface of the fermenting must and into the headspace of the fermentation vessel. From there, it escapes from the vessel through a fermentation lock into the cellar atmosphere, where it will mix with the air. Together with the formed carbon dioxide, other fermentation by-products will also escape the fermenting vessel, such as the aromatic compounds responsible for the sensory perception of the wine. The loss of these sought-after fermentation-derived aroma compounds can result in a reduced concentration of the compounds in the finished wine, potentially lowering the aromatic quality of the wine. A recent study investigated the aromatic losses due to volatilisation and the potential repurposing of the lost fermentation by-products of a Sauvignon blanc wine. Specifically, fermentation-derived carbon dioxide (which serves as a carrier for the naturally-formed aroma compounds) was collected and pressurised. The gas was then used to carbonate water and compared to water carbonated with industrially-produced carbon dioxide. Materials and methods Sauvignon blanc grapes from a vineyard in Lednice, Czech Republic, were processed, and the must was inoculated with IOC Be Thiols yeast. The fermentation gas was captured through a pipe connected to a collection tank based on the principle of an expansion tank with a rubber bag. The fermentation gas was cooled in the collection tank before entering a compression unit fitted with a condensation and filtration unit. After fermentation, the compressed gas was used to carbonate water. The study also included water carbonated with industrially-produced carbon dioxide to serve as a control. The carbonated waters were subjected to sensory analysis. Results • Sensory attributes arising from the sensory evaluation of the water carbonated with fermentation gas included

“bananas”, “pears”, “honey”, “citrus” and “sweets”. “Bananas” and “pears” were the most prominent sensory attributes listed. • Compared to industrially-carbonated water, the wine evaluators rated the water carbonated with fermentation gas much higher in perceived sweetness, while the industrially-carbonated water was perceived as being sourer. Other sensory attributes (savoury, bitter and ferrous) were rated slightly lower in intensity in the water carbonated with fermentation gas when compared to the industrially-carbonated water. • Wine evaluators were asked to assess the wines according to the fineness of the gas bubbles in the carbonated waters. Results showed that the water carbonated with fermentation gas had smaller, more sensorially pleasing bubbles when compared to the industrially-carbonated water. References https://www.wineland.co.za/repurposing-sauvignon-blanc fermentation-gas-for-natural-aroma-enrichment/ Conclusion Fermentation gas naturally enriched with Sauvignon blanc aromatic substances was used to carbonate water. The sensory assessment showed that the captured gas modified the composition of the water resulting in increased fruit aromas and perceived sweetness, while adding sensorially-pleasing bubbles. The results from this study show that a significant amount of compounds are volatilised and lost during fermentation and that the gas can be captured and repurposed. Industrially-produced carbon dioxide is often used in the wine industry as an inert gas for blanketing, sparging and sparkling wine production. Captured fermentation gas could be used for these winery applications as a natural aroma-rich alternative to industrial carbon dioxide. The fermentation gas can also be used in other industries to enrich beverages naturally. Capturing and reusing natural fermentation gas could also improve wineries’ sustainability and carbon footprint. Regulatory implications should be considered as there might be restrictions affecting the legal use of this technique. Abstract Fermentation gas naturally enriched with Sauvignon blanc aromatic substances was used to carbonate water. A sensory assessment showed that the captured gas modified the composition of the water favourably. The repurposing of fermentation gas could be applied in many industries. 

For more information, contact Carien Coetzee at carien@basicwine.co.za.

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TECHNICAL YEARBOOK 2023