South Africa Wine Technical Yearbook 2025

TABLE 1. Main organic acids present in healthy grape must and wine. 2 Acid Source

Typical concentrations in grapes (g/L)

Typical concentrations in wines (g/L)

Tartaric

Grapes

2 - 10

2 - 10

Malic Citric Lactic

Grapes and yeasts Grapes and yeasts LAB* and yeasts

1 - 7

0 - 7

0.1 - 0.7

0 - 0.8

0 0 0

0 - 3

Succinic

Yeasts

0.5 - 1.5 0.1 - 0.5

Acetic

Yeasts, LAB* and AAB**

The table was adapted from its original form as permitted by the Creative Commons License of Oeno One. * Lactic Acid Bacteria; ** Acetic Acid Bacteria.

TABLE 2. Overview of the yeast trial.

Syrah, 100 kg lots (2023 and 2024)

OMEGA LT + KLIMA

FX10

XAROM 20 g/hL

KLIMA

20 + 10 g/hL

SUPERSTART ™ ROUGE 20 g/hL at 20°C LACTOENOS™ BERRY Direct 1 g/hL (24 hours after yeast addition) NUTRISTART ™ AROM 30 g/hL at ⅓ of AF Identical winemaking protocols AF at 25 - 28°C, regular punch downs, seven-day skin contact, racking (2x), SO 2 addition (50 mg/L), bottling three months after vinification.

Putting theory into practice: LAFFORT® yeast trials Experimental layout Four yeast treatments were tested in a winemaking trial carried out in two consecutive vintages (2023 and 2024). These included ZYMAFLORE™ yeasts FX10, XAROM, KLIMA and co-inoculation of OMEGA LT and KLIMA (Table 2), rehydrated in water at ambient temperature (20°C) with SUPERSTART™ ROUGE (20 g/hL). The O. oeni starter LACTOENOS™ BERRY Direct , capable of preserving citric acid during MLF, was inoculated (1 g/hL) 24 hours after yeast addition. At ⅓ of AF, complex yeast nutrient NUTRISTART™ AROM was added. After seven-day skin contact, coinciding with almost simultaneous AF and MLF completion, the wines were racked of skins and stabilised with SO 2 (50 mg/L). Bottling under screw cap occurred three months after vinification, and the final wines underwent detailed chemical and sensory profiling. Main results Despite vintage variation, the main oenological parameters of wines obtained from different yeast treatments showed similar trends (Figure 1).

• Malic acid can be either consumed or produced by wine microorganisms. Most S. cerevisiae strains partially consume malic acid (i.e., approximately 15 - 40%) during AF. 4 Malic acid is transformed into lactic acid through MLF conducted primarily by Oenococcus oeni . • Strains of O. oeni differ in their capacity to degrade citric acid, another grape-derived acid. This can affect both wine acidity and flavour profile, as citric acid is a precursor to several compounds, including diacetyl (buttery aroma). • In addition to MLF, l-lactic acid can also be produced from grape sugars via lacto-ethanolic fermentation by L. thermotolerans . • Absent in grapes, succinic acid is often the third most abundant metabolite formed by fermenting yeast (after ethanol and glycerol). While it has little effect on pH, it contributes significantly to the increase in TA post-AF. • Acetic acid is the main volatile acid in wines, which can be formed throughout various winemaking stages, via yeasts, lactic acid bacteria (LAB), and acetic acid bacteria (AAB). • Other organic acids are also present in grapes and/or in wines in various quantities, including pyruvic, fumaric, gluconic, d-lactic acid, amino acids, fatty acids and others.

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TECHNICAL YEARBOOK 2025