In grape must of high sugar concentration, yeast growth, the viability rate of “resting” yeast cells, and fermentation activity were stimulated under certain conditions of aeration and temperature. This stimulation might be interpreted as being a result of the yeast cell sterol content. The addition of certain sterols to the fermenting medium was able to increase this sterol content. According to aeration conditions of the medium, which determined the sterol content of yeasts, the sterols added in the medium acted as (i) growth factors, (ii) fermentation inhibitors, and (iii) survival factors for the yeast.

The retardation and arrest of fermentation, observed before the complete sugar consumption of high-sugar grape must, come from an inhibition of the yeast metabolism during its decline phase and are variable with the strain. The addition of nutritional growth factors stimulates the initial growth of the yeast but is ineffective in the decline phase. Some substances, known previously as yeast anaerobic growth factors (sterols, oleanolic acid, oxytocin), in some conditions (initially aerated grape must and aerobically cultivated yeast) act by increasing the viability of the resting cells and prolonging their fermentation activity. These substances have been named “survival factors.”

<p style="text-align: justify;">Les levures du genre <em>Dekkera</em>/<em>Brettanomyces</em> sont des cellules caractéristiques, de petites tailles, de forme ogivale. Leur niche écologique a été précisée à partir de prélèvements sur des raisins, des moûts en fermentation, des vins en cours d'élevage ou de conservation en bouteilles, de différentes appellations de la région bordelaise et du Beaujolais; les clones isolés sont identifiés. C'est une levure de contamination des chais et du matériel vinaire. Leur incidence sur les caractères organoleptiques des vins a été étudiée: cette étude a confirmé que c'est généralement une levure d'altération modifiant profondément la qualité des vins.</p>