<p style="text-align: justify;">Weak malolactic fermentations in wine making are often attributed to the medium constituents such as ethanol and SO₂. However, some authors report that the interactions between <em><em>Saccharomyces cerevisiae</em></em> and <em>Leuconostoc oenos</em> could be responsible too.</p><p style="text-align: justify;">The aim of this work is to characterize the influence of <em>S. cerevisiae</em> on the growth of <em>L. oenos</em>. First, a qualitative study was performed on solid medium containing 8 g/l of L-malic acid. In this case, <em>L. oenas</em> was mixed to M.R.S agar and poured into Petri plate, then <em>S. cerevisiae</em> was seeded in rings on the agar surface. After incubation, the coculture result in an inhibition of <em>L. oenos</em> growth by <em>S. cerevisiae</em>.</p><p style="text-align: justify;">In order to quantify this phenomenon, a culture of <em>L. oenas</em> was carried out on liquid medium prefermented by <em>S. cerevisiae</em> (supplied with M.R.S nutrients) and was compared with a control on M.R.S medium. Both contained 8 g/l of L-malic acid. This technique allows to separate the microorganisms in order to avoid competitions between the strains.</p><p style="text-align: justify;">The prefermented medium affects <em>L. oenos</em> growth and the malolactic fermentation, but the results depended on the pH and the temperature. Globally, low pH (3,4) and high temperature (30°C) conditions increased the inhibitory effect of the prefermented medium. This medium contains inhibitory molecules for <em>L. oenas</em>. In agreement with some authors, those molecules could be the medium chain fatty acids (C₈ to C₁₂) released in the medium by <em>S. cerevisiae</em> because of their pH-dependent toxicity. However, those results may be different with other couples of strains of <em>S. cerevisiae</em> and <em>L. oenos</em>.</p>

The Lactobacillus acidophilus growth was investigated to find the optimal concentrations of 2 nitrogen sources (thought to be in excess) and 2 organic acids. A Plackett and Burman experimental design was used allowing identification of the more imlx)rtant factors with very few experiments. In the studied range, all the factors had a linear effect and a great influence on the final viability. 20 g/L of each nitrogen sources, 3 g sodium-citrate/L and 5 g sodium acetate/L are necessary, pH, temperature and glucose had poor influence.

J. Inst. Brew. 114(1), 69-75, 2008Yeast Brettanomyces bruxellensis is a contaminant found worldwide and is responsible for red wine spoilage due to the development of animal and phenolic off-odours. During this study, 24 Brettanomyces bruxellenis isolates were obtained from red wine samples from two French wineries and these were discriminated as 23 strains. Nine strains coming from 2 wineries and 4 vintages were cultivated in synthetic wine medium for 1500 hours and they gave nine different behaviours. Four main growth patterns (with different growth steps and durations) and three main different sugar consumption profiles were obtained. Glucose and fructose were not limiting substrates for all strains. The production level of 4-ethylphenol was found to vary from strain to strain (from 0.350 to 2.773 mg L -1 ) and was independent of the biomass concentration. Some strains presented a coupled-togrowth production of volatile phenols, others did not. This study showed that different strains of Brettanomyces bruxellensis behaved differently, one from another, under the given conditions taking into consideration several aspects. The results thus demonstrate a large intraspecific diversity.