South Africa Wine Technical Yearbook 2025

10 15 20 25 30 35 40 45

1 000 1 500 2 000 2 500 3 000 3 500

1 000 1 500 2 000 2 500 3 000 3 500

1

12000

1

10000

8000

6000

Aromatic index

4000

Ester concentration (µg/L)

Ethyl esters (µg/L) Acetate esters (µg/L)

Ethyl esters (µg/L)

Ethyl esters of fatty acids Acetate esters of higher alcohols

Acetate esters (µg/L)

0 5

0 500 KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21°C

0 500

3011,5 1817,5

7355 6186

2000

KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21 °C KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21°C 2157 1463 4MSP 3SH 3SHA FIGURE 1. Volatile thiol production by two yeasts fermented at different temperatures in Sauvignon blanc must. 8

°C

11150 10160

0

KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21°C KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21°C

FIGURE 3. Acetate esters formed by two yeasts fermented at different temperatures in Sauvignon blanc must. 8

els of volatile thiols esters in Sauvignon blanc wines fermented at two temperatures (means of duplicates).

emperatures (means of duplicates).

1 000 1 500 2 000 2 500 3 000 3 500

12000

10000

such as 18°C instead of 13°C, while also conserving energy compared to fermenting at 13°C. However, to render the wine more appealing to specific consumers or increase the overall complexity of aromas, a slightly lower fermentation temperature (e.g., 16°C) can be employed to enhance ester retention, while reducing energy consumption compared to fermentation at 13°C. Fermentations may also be initiated at higher temperatures to facilitate thiol release and conversion, followed by a reduction towards the end of fermentation to prevent ester volatilisation. 2000 4000 6000 8000 Acetate esters (µg/L) Conclusions Experimenting with fermentation temperatures is a worthwhile consideration for winemakers seeking to minimise their energy footprints during white wine production. Winemakers are encouraged to: • Collaborate with yeast suppliers to run fermentation trials at slightly higher temperatures. • Explore new yeast strains well-adapted to 0 KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21°C higher-temperature fermentations, such as 18°C instead of 13°C, without compromising aroma or fermentation reliability. • Experiment with temperature variation by initiating fermentation at elevated temperatures and then lowering the fermentation temperature towards the end of the process. Optimising fermentation temperature is a straightforward intervention that, if carefully managed, can contribute meaningfully to environmental targets, while maintaining or even enhancing wine quality. 

Ethyl esters (µg/L)

0 500

_21 °C

KLIMA_16 °C KLIMA_21 °C XAROM_16 °C XAROM_21°C

formation depends more on acetyl transferase enzymatic activity (e.g., Atf1p) and less on substrate concentration. ZYMAFLORE TM yeasts and fermentation temperature Fermentation experiments were conducted in Bordeaux using ZYMAFLORE TM XAROM and ZYMAFLORE TM KLIMA in Sauvignon blanc grape must at 16°C and 21°C. 8 Wines produced at 21°C demonstrated significantly higher concentrations of varietal thiols than those fermented at 16°C (Figure 1). Conversely, concentrations of mainly the ethyl esters were reduced at the elevated temperature, underscoring the necessity of aligning the yeast strain with FIGURE 2. Ethyl ester production by two yeasts fermented at different temperatures in Sauvignon blanc must. 8

wo temperatures (means of duplicates).

the desired wine style (Figures 2 & 3). Practical guidelines for winemakers

A winemaker seeking to enhance mainly thiol aromas in a wine can achieve this by fermenting with ZYMAFLORE TM KLIMA or ZYMAFLORE TM XAROM at higher temperatures,

For more information, contact Morné Kemp at morne.kemp@laffort.com. Reference https://www.wineland.co.za/wine-yeasts-and-energy-saving-in-wineries/

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TECHNICAL YEARBOOK 2025