Qymyz is a traditional acidic and ethanolic beverage in central Asian countries made from mare milk fermentation with lactic acid bacteria (LAB) and yeasts. Modeling the growth of microorganisms during fermentation is one of the methods used to control the quality of fermented products. The objective of the study was, firstly, to model the growth kinetics of Kazachstania unispora found in qymyz, and, secondly, to understand their interaction with Lacticaseibacillus casei and Lactobacillus kefiri during the fermentation of mare milk. The K. unispora optimum values of pH and temperature were 4.81 ± 0.22 and 30.16 ± 0.53 °C, respectively, with an optimal growth rate (µopt) of 0.56 ± 0.02 h−1. K. unispora had an ethanol production rate of 6.1 × 10−8 mg·CFU−1. Growth, in terms of limiting substrates showed a lower Ks value for galactose at 0.13 ± 0.04 mg·mL−1 with µopt of 0.45 ± 0.01 h−1, while, for glucose, the Ks was 0.24 ± 0.03 mg·mL−1 with the same µopt. Cocultures of K. unispora were conducted with L. casei and L. kefiri in a synthetic medium and mare milk. The results showed that K. unispora growth was limited and, thus, its ethanol production capacity was inhibited. VOC analysis of mare milk fermented with the studied strains and their cocultures resulted in 37 major volatile compounds. Statistical analysis of the VOC profiles showed that K. unispora modulates the aroma production in coculture with LAB.
