## 4 Discussion  
The high-throughput sequencing technique provide a very useful tool for the rapid and exhaustive characterisation of microbial populations connected with wineries and wine production [19]. Recently, there have been numerous reports from many countries with wine-making traditions on the influence of various factors on the microbiota of grapes, wines, and the environments connected with them [28; 29]. This is the first report from Poland in which the reader can find information about Polish red wines as analysed using a metagenomic approach. The literature provides evidence that the abundance and diversity of microorganisms in spontaneously fermented wines depend on grape microbiota, the course of fermentation, the metabolites produced, and environmental conditions [18; 19]. Generally, among fungal populations found in vineyard grapes, the most frequently occurring yeast genera are _Hansenispora_, _Saccharomyces_, _Candida_, _Debaryomyces_, _Metschnikowia_, _Pichia_, _Torulaspora_, _Zygosaccharomyces_, _Saccharomyces_, _Brettanomyces_, _Cryptococcus_, _Isaatchenkia_, and _Starnerella_[30; 31; 32]. Many of these yeasts have also been reported to be present in musts during alcoholic fermentation [33; 34; 35]. The Polish red wines had similar populations of yeasts, among which _Saccharomyces_, represented by _S. cerevisiae_ and _S. caricamus_, was the most abundant genus. Moreover, _Hansenispora_ and _Candidia_ were present in all the wines, while _Pichia_, _Torulaspora_, _Metchnikowia_, and _Lachancea_ were detected in two of the three wines. Bacterial communities are usually more plentiful and varied than yeast communities on grapes, in must, and in wine. According to the literature, the most abundant bacteria found on vineyard grapes belong to the taxa _Firmicutes_, _Lactobacillus_, _Bacillus_, _Enterobacteriales_, _Pseudomononadales_, _Rhodospirilliales_, _Pasteuellales_, _Bacteroides_, and _Actinobacteria_[33; 34; 36]. On the other hand, bacterial populations in musts are limited to _Lactobacillus_, _Bacillus_, _Enterobacteriales_, _Pseudomononadales_, _Rhodospirilliales_, and _Oenococcus oeni_[33]. In the present study, we detected many of these groups of bacteria, namely _Lactiplantiobacillus_, _Bacillus_, _Enterobacter_, and _Gluconobacter_. _Oenococcus_ was not found in any of the wines, while _Tatumella_ was present in all samples. It has been stated that many bacterial genera and species have a wide range of occurrence. Nevertheless, fermentation usually reduces microbial diversity in favour of _Saccharomyces_ yeasts. The Polish red wines obtained from grapes of the Regent variety had different TPC and DPPH radical scavenging activities and distinct glucose, fructose, and lactic acid concentrations, but they did not differ significantly in ethanol concentration. Generally speaking, the investigated wines contained similar concentrations of ethanol and organic acids, and had pH, TA, TPC, and DPPH values similar to those determined by other authors in wines of the same grape variety, independent of the country of origin [37; 38; 39; 40]. It is interesting that ethanol concentration values in our wine samples, which were obtained using spontaneous fermentation, were similar to those reported by [PERSON] et al. [39] and [PERSON] et al. [38], in whose studies the active yeasts _S. cerevisiae_ were used to run the fermentation, and the values reported in [PERSON] et al. 's work [40], in which sequential fermentation with _Metchnikowia_ or _Hansenispora_ cultures together with _S. cerevisiae_ was carried out. The associations between the characteristic microbiota and the physicochemical parameters of wines are interesting but rarely touched upon in the scientific literature.