South Africa Wine Technical Yearbook 2025

OCTOBER

Over the past few decades, the wine industry has increasingly relied on selected microorganisms to enhance the reliability and predictability of fermentation. While this has brought consistency and quality to winemaking, emerging consumer expectations around sustainability are prompting producers to look further. One less-explored strategy with promising potential is the use of specific yeast strains to reduce energy consumption in wineries. Why cooling matters A major source of energy use in wineries is refrigeration. According to a recently published report by the OIV, “Energy saving in winemaking – impact of alcoholic fermentation,” 1 approximately 90% of a winery’s electricity bill is linked to cooling processes, including controlling fermentation temperature, cold stabilisation and cold storage. Among these, fermentation temperature control is particularly demanding, accounting for up to 45% of total energy consumption. Fermentation produces heat, and the production of white and rosé wines, in particular, requires precise temperature control to preserve aroma and freshness. This means that winemakers must continuously apply cooling during fermentation, an energy-intensive process. Small changes, big impact Traditionally, lower fermentation temperatures are believed to yield more aromas, particularly in the production of white wine. However, research suggests that this assumption does not always hold. In fact, the optimal fermentation temperature varies depending on the yeast strain and the specific fermentation conditions. The OIV report mentions several research projects that have demonstrated that modest increases in fermentation temperature can lead to substantial energy savings without compromising the wine’s sensory or chemical profile. • An increase in the fermentation temperature of 4°C (from 15°C to 19°C) of a Chardonnay sparkling base wine resulted in an approximately 65% reduction in energy use, with no measurable differences in chemical parameters or sensory characteristics. 2 Wine yeasts and energy saving in wineries By Ana Hranilovic & Karien O’Kennedy

ADOBE STOCK

• An increase in fermentation temperature of 5°C (from 14°C to 19°C) in a Riesling must resulted in energy savings of up to 70% with no impact on wine quality. 3 • In fermentations of Glera (for Prosecco) and Pinot grigio musts, energy savings of up to 35% were obtained when temperatures were adjusted from between 15°C and 17°C to 19°C, with no significant impact on chemical parameters or sensory outcomes. 4 Fermentation temperature and wine aroma Over the past few decades, numerous studies have investigated the effect of fermentation temperature on wine aroma. A study conducted in New Zealand on Sauvignon blanc yielded results similar to those reported by the OIV, comparing fermentations at 12.5°C and 25°C. 5 Despite variations in the wine’s chemical parameters, a sensory panel could not perceive significant differences in 75% of the wine pairs fermented at the two temperatures. For the 25% of wines where sensory differences were identified, the wines fermented at 25°C were unexpectedly perceived as fruitier, primarily due to elevated concentrations of the varietal thiol, 3SH (3-sulfanylhexan-1-ol). The researchers concluded that fermentation at higher temperatures could reduce energy costs without adversely affecting wine quality. Studies generally indicate that the concentrations of the two varietal thiols, 4MSP (4-methyl-4-sulfanylpentan 2-one) and 3SH, increase with increasing fermentation temperature. However, the academic literature presents conflicting results regarding 3SHA (3-sulfanylhexyl acetate), an acetate thiol formed from 3SH during fermentation, as well as other fermentation esters. 6 This discrepancy can be partially attributed to the manner in which the experiments were conducted. For example, 3SHA has higher volatility than 4MSP and 3SH, and can be lost via volatilisation if the fermentation is maintained at an elevated temperature. The two major groups of wine esters are ethyl esters of fatty acids and acetate esters of higher alcohols. 7 The levels of ethyl esters primarily depend on the concentration of their fatty acid precursors (e.g., butanoic acid, hexanoic acid and octanoic acid), which, in turn, are strongly influenced by fermentation conditions. For instance, challenging conditions such as lower temperatures and low turbidity can enhance the formation of medium-chain fatty acids (MCFAs) and, consequently, their corresponding ethyl esters. This behaviour contrasts with acetate esters, whose

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TECHNICAL YEARBOOK 2025