053: A Thiol Trapping System to Improve Wine Quality Thiol Trapping System to Improve Wine Quality

Introduction

Thiols are key aroma compounds in wine formed from grape precursors during fermentation. In anaerobic environments, reductive aromas are attributed to the formation of methyl and ethyl thiols which are unpleasant to the consumer. Additionally, recent events of wildfires in various wine-growing regions led to smoke taint, which adversely affected the wine's overall quality. Thiophenols are among the compounds responsible for smoke taint in wine. The ability to selectively remove specific amounts of thiols could improve the wine's quality without altering other quality parameters.

Methods

An inert closed-loop system was devised, and simple solutions were tested as a proof of concept on ethyl thiol and thiophenol. The thiol was added to a buffer solution in a source flask, while 5,5’-dithiobis(2-nitrobenzoic acid) (DTNB), a known thiol quantification compound, was used to trap the volatile thiols in a separate flask. This system ensured that the trapping solution would not mix with the initial solution/wine. Aliquots were drawn from the source and trapping flask and the absorbance was taken with a UV-Vis spectrophotometer to quantify the amount of thiol trapped. The parameters suspected to influence the trapping efficiency were investigated, including the concentration of thiol, the concentration of DTNB, the size and number of bubbles, the buffer solution, pH and temperature.

Results

Thiols could be trapped with the proposed non-contact system. After 60 minutes, approximately 85% of the ethyl thiol added was trapped. While the heavier thiophenol took longer to trap, the trapping efficiency could be increased by raising the temperature or introducing a nebulizer. Furthermore, adjusting the pH of the source flask allows for the selective removal of ethyl thiol over thiophenol.

Significance

Removing volatile thiols associated with reduction or smoke-taint in wines is the stepping stone to developing a selective column that is food safe and can be incorporated into winemaking processes. Further research would verify the selectivity of the process and include other reductive faults like H2S. The column could benefit the winemaking community by possibly mitigating the impact of wildfire events or improving reductive wine quality.

Authors: Lik Rong Lim, Elizabeth Tomasino, Michael Penner