Comparative metatranscriptomics of bacterial and yeast communities of two milk kefir beverages (MKAA1 and MKAA2) obtained by fermentation with two different frozen stocks of the kefir grain CIDCA AGK1, and differing in rheological features and organic acid amounts production was carried out to figure out the relation between differences in physicochemical and rheological properties of kefir and the microbial active profile associated with each product. The dominance of lactic acid bacteria and yeast and a marginal amount of acetic acid bacteria marked the microbiome. The bacterial families Lactobacillaceae and Streptococcaceae account for almost all bacterial gene transcripts, with Lactobacillus helveticus, L. kefiranofaciens, L. gallinarum and Lactococcus lactis being most frequent in the microbiome of MKAA1 beverage, and L. kefiranofaciens, Lc. lactis and Leuconostoc mesenteroides being most prevalent in the MKAA2. Dipodascaceae and Saccharomycetaceae were the leading yeast families represented by Yarrowia lipolytica, Saccharomyces unisporus, and Kluyveromyces marxianus. The MKAA1 and MKAA2 shared >75% KEGG Ortologs (KO) in bacteria and yeast libraries. Considerable decreases in total expressed genes (KEGG Ortolog) assigned to Lactobacillus helveticus and L. gallinarum might be related to the variations in rheological features of the beverages, probably by compromising the interrelations with L. kefiranofaciens which might explain the variations in rheological features of the beverages.