The lactic acid bacterium Oenococcus oeni is used as starter culture for the degradation of malic acid during winemaking. This microorganism could only be grown to high cell densities in complex media supplemented with tomato juice. For the characterization of so far unknown growth stimulating factors pressings or extracts from fruits or leaves were prepared and tested for their growth stimulating properties. Grape juice and peel extracts from mango exhibited the highest growth promoting properties when added to culture media of oenococci. Elementary analysis in combination with solid phase extraction revealed that the manganese concentration of the juices and extracts was one of the factors responsible for growth stimulation. It became obvious that two growth optima existed, one at 67 µM and the other 34 mM. Most likely the activity of enzymes which use manganese as cofactor are stimulated at micromolar concentrations, while at millimolar concentrations manganese can form oxidation protecting complexes. The manganese concentration in the applied growth media for oenococci is much lower than that found in this study for optimal growth. The addition of other minerals to the basic culture medium had no extra stimulating effect. A determination of the titre of cells grown in the presence of fruit juice fractions obtained after treatment with cation exchange resin as well as lemon mesocarp extracts with a low manganese content revealed that the growth stimulating properties of some extracts could not be explained by the presence of manganese alone. Organic compounds, most probably polyphenols, were responsible for the further growth stimulation as revealed by polyvinylpolypyrrolidone treatment of the fruit juices. This may be the explanation for the rapid growth start and the high cell titre of oenococci observerd in culture media supplemented with polyphenolic compounds. We recommend that you consult the full text of this article, which was published in Deutsche Lebensmittel-Rundschau, 2005, 101 (7) 286-293