Microbiologically unstable wine contains growing and metabolically active microorganisms which convert wine compositions into completely different components. Microbiologically instabile wine differ by their turbidity, sediment and/or foaming, and therefore wine destined for bottling has to be microbiologically stable. The signs of instability are observed as turbidity, which is often caused by certain species of yeast and bacteria. In the frame of this master thesis we analysed 57 samples of white, red and orange wines. They were evaluated by quality test methods, which included on air testing as well as in incubator testing, measurements of turbidity, spectroscopic methods and quantification of microorganisms on selective solid media. Further, these microorganisms were identified by using molecular methods for yeasts and bacteria. Our results showed that red wine samples had an increased turbidity. We identified thirteen different species of microorganisms, which includes yeasts Saccharomyces cerevisiae, Zygosaccharomyces bailii, Dekkera bruxellensis, Pichia manshurica, Nakazawaea holstii, Pichia membranifaciens, Saccharomyces paradoxus, Saccharomyces kudriavzevii, lactic acid bacteria Oenococcus oeni, Lactobacillus hilgardi, Lactobacillus casei, Pediococcus parvulus and acetic acid bacteria Acetobacter pasteurianus.
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