South Africa Wine Technical Yearbook 2025

DECEMBER

SHUTTERSTOCK

Yeast-derived acidification of red wines By Ana Hranilovic and Charlotte Vion

yeast strains during fermentation. 2 This includes lactic acid production through the unique sugar metabolism of Lachancea thermotolerans , used either in simultaneous or sequential inoculation with Saccharomyces cerevisiae . 3 Another approach is the use of novel S. cerevisiae strains capable of preserving or even producing malic acid during alcoholic fermentation (AF). 4 Higher levels of malic acid post-AF translate to increases in lactic acid after malolactic fermentation (MLF), an acid that is both microbially and chemically stable. This article presents results from fermentation trials conducted during the 2023 and 2024 vintages, highlighting the impact of LAFFORT ® ZYMAFLORE™ strains on wine acidity, along with other chemical and sensory parameters. But first, some facts about wine acids • Six organic acids account for > 95% of organic acids in wine (Table 1). The primary grape-derived acids are tartaric acid and malic acid. Tartaric acid is not metabolised during winemaking, but can be lost due to precipitation with potassium or calcium ions.

Acidity is a key quality parameter in wine. It defines not only its taste and style, but also its appearance, microbial stability and ageing potential. 1 In warm climates or vintages, grapes at harvest often lack acidity and require acid correction. As global temperatures continue to rise, ripening is increasingly shifted towards the hottest period of the year. High temperatures accelerate malic acid respiration in berries, thereby further exacerbating the acidity loss. As a result, winemakers increasingly rely on exogenous acidification of grapes, mainly via tartaric acid addition and less so with other organic acids (i.e., lactic, malic, citric and, as of recently, fumaric). However, these practices are tightly regulated and subject to labelling requirements. 1 Moreover, tartaric acid is susceptible to instability and precipitation, thereby imposing additional cost implications. As a result, there’s growing interest in approaches that help maintain acidity without relying on costly additives. The solution One promising strategy is biological acidification, or bioacidification, which involves the use of acidifying

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TECHNICAL YEARBOOK 2025