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Preparing of sourdough is one of the oldest biotechnological methods, but the research is still going on and is crucial. In Latvia the spontaneous sourdough is used in traditional rye bread baking which microflora is determined in flour and in microorganisms cultures presented in external environment. Literature data proved that spontaneous sourdough presents several lactic acid bacteria (LAB) and yeasts. Lactobacilli present in sourdough are both homofermentative and heterofermentative and depending on temperature can be presented as well as mesophylic and thermophilic. The latter present in scalding are essential to ensure technologocal process of rye bread. Metabolites of thermophilic LAB are responsible for providing sufficient dough acidity. Besides LAB sourdough contain yeasts including Saccharomyces cerevisiae, Pichia saitoi, Candida crusei, etc. The aim of the research was to analyze growth dynamics of microflora in three-stage spontaneous rye flour sourdough fermentation process and to isolate some of its representatives. One of the basic tasks for applying the research was to acquire methods of micro-organism identification. Results of experiments show predominance of LAB reaching 6.06 log10 cfu ml-1, high amount of yeasts reaching 5.22 log10 cfu ml-1 and a final pH value 3.83 representing that this sourdough has desirable properties for preparation of rye flour sourdough starter. For identification of LAB cultures API CH 50 test was acquired while ID 32 C for yeasts. Results of the experiments reveal heterofermentative LAB Lactobacillus Brevis and Saccharomyces cerevisiae yeast presence in sourdough. These microorganisms are typical members of sourdough microflora with reference to foreign scientific publications. [ABSTRACT FROM AUTHOR]