Background. Whey, a waste product from cheese production, is an underutilized raw material with high nutritional value. This waste product may be used in the production of fermented  beverages. The aim of this study was to develop an innovative fermented beverage based on whey and fruit vinegar and to determine the survivability of two probiotic strains of lactic acid  bacteria. The study included the preparation of individual components, the selection of their appropriate proportions and the verification of the influence of storage conditions and time on the  survivability of the strains. The biological material consisted of Saccharomyces cerevisiae wine yeast strain, Acetobacter pasterianus O4 and Acetobacter pasterianus MW3 acetic bacteria strains  and lactic acid bacteria strains: Lacticaseibacillus rhamnosus GG ATCC 53103 and Lactiplantibacillus plantarum LMG P-21021. The survivabilityl of lactic acid bacteria was tested under  anaerobic conditions. The beverage was made of whey mixed with 10 % to 50 % apple cider vinegar. The above beverage was kept at a temperature of 21 ± 2 °C and 3 ± 2 °C for 21 days.
Results and conclusion. The beverage was analyzed once a week, and the number of lactic acid bacteria after 21 days of storage was at a high level, exceeding the WHO recommended number of  bacteria in probiotic beverages – 106 ÷ 107 CFU/cm³. The beverage based on whey and the addition of 10 % vinegar was a good medium, and the number of lactic acid bacteria in each variant of  the beverage was on average 8.4 ± 0.29 log CFU/cm³.