The purpose of this work was to characterize flavour compounds from rye flour leavens started with six mixed lactic acid bacteria (LAB). This material after fermentation is used in Poland for preparing sour soup (Polish “żurek”). The volatiles were isolated after 1, 2 and 3 day of fermentation using static and dynamic headspace techniques; organic acids, pH, titratable acidity and bacteria count were monitored. Gas chromatography analyses were performed with capillary columns of different polarities connected to flame ionization detector, electron capture detector and mass spectrometer. The organic acids were analysed by high performance liquid chromatography with HPX-87H column and Dual Adsorbance Detector. Totally 18 compounds were identified including 5 esters, 4 alcohols, 6 carbonyls, 2 organic acids. Ethyl lactate, ethanol, acetoin, lactic acid and acetic acid were prevailing compounds present in ppm levels. The number of lactic acid bacteria and organic acid production were correlated. Sensory quality of leavens aromas was elucidated by sensory descriptive method. Concerning all the data measured it can be concluded that the optimum quality results were obtained in the leaven started with mix of three strains of Lactococcus lactis ssp. lactis.