# Adding Flavor to Beverages with Non-Conventional Yeasts
## 4 Discussion  
In our study we have screened non-_Saccharomyces_ cerevisiae yeast biodiversity in order to identify strains with more pronounced volatile compound formation than present in lager yeast strains. Pronounced differences in aroma alcohol production were identified between _S. cerevisiae_ and lager yeast strains, as expected from a clean pilsner beer produced by lager yeasts versus the more complex flavors produced by ale and wine yeasts. In our screening, we identified _W. anomalous_ strains as the most dominant flavor producers, which also included production of substantial amounts of acetic acid. The formation of floating cell layers such as seen for the _W. anomalous_ strains has been reported as a typical phenomenon in stored wines [20]. Yeast biodiversity holds a plethora of strains that show useful characteristics such as ethanol production and flavor formation. This requires a detailed evaluation of the initially identified favorable strains under different conditions, particularly in co-fermentation regimes [21]. It will be challenging to identify the most suitable co-fermentation setups, as flavor profiles will certainly be influenced by different ratios of non-conventional yeasts versus standard brewing strains. In earlier studies, _W. anomalous_ strains have been isolated from a range of cereal-based sources. It has been reported from sourdoughs and was found as the dominating yeast in sourdough microbial ecosystems next to _S. cerevisiae_. The prevalence of the fungus was associated with its osmotolerance and increased acid tolerance in comparison to _S. cerevisiae_[22]. Furthermore, it was shown that _W. anomalous_ provides some antimicrobial activity, e.g., mycocin production, that can be used to prolong the shelf life of bread [23; 24]. Other _Wickerhamonyces_ species have been put to use in baking using microbread baking platforms. Specifically, bread obtained with _Kazachstania ganospora_ and _Wickerhamonyces__subpelliculosus_ provided added broader aroma profiles compared to control baker's yeast [25]. _P. kluyveri_ CBS 188 produced a total of 41 volatiles during our fermentations. Yet, it was outstanding in its ester profile, e.g., ethyl acetate, isoamyl acetate or phenethyl acetate that was several folds higher than in the reference lager yeast strain _WS34/70_. _P. kluyveri_ strains are found in \"wild fermentations\" of wine but it is also commercially available to boost flavour production through sequential fermentations. _P. kluyveri_ strains together with strains of _K. marxianus_ were also presented as potential starter yeasts for controlled cocoa fermentation [26]. Based on increased demand for natural flavors produced from yeasts, the use of non-conventional yeasts as platform strains for the production of aroma volatile has gained attention. Hence, _K. marxianus_ was suggested as a cell factory for flavor and fragrance production based on several advantageous traits, e.g., thermotolerance and the wide array of volatile molecules it produces [27]. We had one strain of _K. marxianus_ (CBS 1557) in our collection. However, this strain was as low in aroma-compound production as our lager yeast reference. This indicates the need to obtain a larger collection of strains of one species and also to analyse volatile compound formation under different nutritional regimes and fermentation conditions [28]. It further requires the implementation of high-throughput screening tools and assays to identify suitable strains, which was actually successfully shown for _K. marxianus_ strains producing ethyl acetate [29]. Additionally, it requires more effort to acquire genomic, transcriptomic and metabolomic datasets of non-conventional yeasts in order to bridge the knowledge gap about _S. cerevisiae_[12; 30]. That said, our approach to screening non-conventional yeasts in non-industrial fermentation broths only provides an initial glance of the volatile production capabilities of the tested strains.