Technical Yearbook 2024

Conclusion Results from the study suggest that the number of inoculated yeast cells could affect not only the fermentation rate, but also the formation and release of potent aroma compounds such as the volatile thiols. Adjusting this fermentation parameter could potentially lead to increases in 3MH and 4MMP, which may result in wines with more intense sensory characteristics, such as passionfruit and blackcurrant. However, further work is needed to ascertain whether this is true for juices of varying composition, volumes and yeast strains. The scientific explanation for the observations in the study also needs to be clarified. The inoculum size is a parameter which can be easily adjusted and does not require specialised equipment or monitoring; however, it will add to production costs. Abbreviations 4MMP: 4-mercapto-4-methylpentan 2-one; 3MH: 3-mercaptohexan-1-ol; 3MHA: 3-mercaptohexyl acetate.  The number of yeast cells present during fermentation had little effect on the concentration of 3-mercaptohexyl acetate (3MHA), and all the wines had relatively similar levels.

parameters (alcohol, pH and titratable acidity) of the resulting wines. However, a trend in alcohol reduction was observed as the inoculum size increased. The highest inoculum size (1 x 10 12 yeast cells/mL) resulted in a 0.17% v/v reduction in alcohol compared to the control wine. Interestingly, the volatile thiol concentration in the resulting wines differed significantly depending on the yeast inoculum rate. As the inoculum size increased, the 3-mercaptohexan 1-ol (3MH) concentration also increased. However, this increase was not linear. An increase in the yeast population from 1 x 10 6 to 1 x 10 8 cells/mL resulted in a 10% increase in 3MH concentration, while an increase from 1 x 10 6 to 1 x 10 10 cells/mL resulted in a 24% increase. However, further increases in yeast cell density (to 1 x 10 12 cells/mL) did not result in any further increases in 3MH. Similarly, 4-mercapto-4 methylpentan-2-one (4MMP) concentration also increased with yeast cell density; however, the increase was linear in this case. Increasing the yeast population from 1 x 10 6 to 1 x 10 8 cells/mL resulted in an 11% increase in 4MMP concentration while increasing the yeast population from 1 x 10 6 to 1 x 10 10 cells/mL resulted in a 69% increase. Further increases in yeast cell density (to 1 x 10 12 cells/mL) resulted in a significant change in 4MMP concentration, resulting in a wine with a 153% increase in 4MMP compared to the control wine.

recommended yeast inoculum rate. However, a recent study questioned the effect of varying the yeast population at the time of inoculation and how it affects the overall fermentation performance of a commercial wine yeast with a particular focus on the formation of volatile thiols, which are potent aroma compounds responsible for an array of fruit-driven sensory descriptors such as passionfruit, grapefruit, blackcurrant and guava. Materials and methods Small-scale fermentations were carried out in 750 mL bottles using 700 mL of sterilised Sauvignon blanc juice (Marlborough, New Zealand). The juice was inoculated with rehydrated Saccharomyces cerevisiae X5 yeast (Laffort), and fermentation was conducted at 15°C until dryness. The juice was inoculated at four different yeast population rates: • 1 x 10 6 yeast cells/mL (control)

• 1 x 10 8 yeast cells/mL • 1 x 10 10 yeast cells/mL • 1 x 10 12 yeast cells/mL. Results Ferments inoculated with an increased number of yeast cells

finished the fermentation one to two days earlier than the control. This result is expected as a higher yeast cell density will increase the volumetric productivity of the fermentation process, thus making the fermentation process faster and more robust. There were no significant differences in the general oenological

Reference https://www.wineland.co.za/yeast-cell-density-and-the-effect-on-volatile-thiol-formation/

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

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TECHNICAL YEARBOOK 2024