3.2.2. Organic Acids

From practical experience, wines with l-malic acid levels below 1 g/<sup>L</sup> are not as conducive to MLF by *O. oeni*, as are wines with l-malic acid concentrations between 2 and 4 g/L. Wines with levels of l-malic acid above 5 g/<sup>L</sup> often start l-malic acid degradation, but do not go to completion. The cause is thought to be the result of the inhibition of the bacteria by increasing concentrations of l-lactic acid derived from the MLF itself. Since acidification with the organic acids lactic acid, <sup>l</sup>(−) or dl malic acid, l(+) tartaric acid and citric acid is authorized in many wine regions, and Vincent Gerbaux from the Institut Français de la Vigne et du Vin (IFV) in France has studied the influence of organic acid additions on the development of MLF (data not published). In this study, six selected wine LAB strains were inoculated into a Chardonnay wine, and five selected *O. oeni* wine LAB strains were inoculated into a Pinot noir wine, both of which were adjusted to a pH of 3.25. Increasing the amounts of l-malic acid, 0.75 to 5.2 g/<sup>L</sup> for Chardonnay and 3.0 to 5.7 g/<sup>L</sup> for Pinot noir, increased the time required to complete MLF, but the speed of l-malic acid degradation increased with increasing content of l-malic acid. The differences between selected wine LAB strains were observed. The addition of D-malic acid had no noticeable effect on MLF.

The presence of l-lactic acid in the wine inhibits the implantation and growth of the inoculated *O. oeni* strains, resulting in an inhibition of MLF. An initial content of l-lactic acid in the range of 1.5 g/<sup>L</sup> slows MLF, but a content of 3.0 g/<sup>L</sup> inhibits MLF by most of the tested *O. oeni* strains. Problems inducing MLF by inoculation with selected wine LAB cultures may be encountered when l-lactic acid was added to must or wine or in wines with a partial MLF. The impact of dl-lactic acid and d-lactic acid has ye<sup>t</sup> to be investigated.
