The objective of this study was to determine the impact of the fermentation conditions on the quality of leavens produced from red beets and their suitability to make red-beet soup (borscht), a traditional Polish dish. Leavens fermented traditionally with a slice of rye bread as well as with the addition of Lactobacillus plantarum starter culture against a control sample without any additives were evaluated. On the basis of microbiological analyses, sensory evaluation of colour, taste and smell and instrumental assessment of colour and dye content, all the examined leavens were described as suitable to make borscht. All the leavens were assessed as safe for health because the level of nitrites was very low and these ions were absent in samples with the addition of L. plantarum. The pH level in all leavens was below 4.5, which protected them against the development of the majority of pathogenic bacteria. The sample’s acidity was found to increase the quickest in samples with the addition of the starter culture.