# Evolution of Aromatic Profile of _Toruslapora delbrueckii_ Mixed Fermentation at Microbrewery Plant
## 1 Introduction  
In the last years, there has been a worldwide growth in microbreweries, which leads to competition in the beer market to find new beers and also those that are characterized by peculiar aroma taste. To achieve this, the brewers paid attention to the ingredients which are water, malls, hops, and yeast [1; 2; 3; 4]. In particular, the brewers focused their attention on the yeast strains to use in brewing fermentation which are selected not only for their good fermentation efficiency but also for their characteristic aroma and flavors.  
In this regard, several recent investigations were focused on the selection of non-conventional yeasts [5; 6; 7; 8]. Non-_Saccharomyces_ yeasts represent a large source of biodiversity to produce new beer styles. In the last years, different non-_Saccharomyces_ yeasts were proposed in brewing, such as _Brettanomyces bruxellensis_, _Toruslapora delbrueckii_, _Candidia shehatae_, _Candidia tropicalis_, _Zygosaccharomyces rouxxii_, _Lachancea thermodeleras_, _Saccharomyces ludwigii_, and _Pichia kuyveri_[9; 10; 11; 12; 13]. _T. delbrueckii_ is one of the most well-known non-_Saccharomyces_ yeasts and it can be found in wild environments such as plants and soils as well as in wine or in fermented food processes. In the brewing process, _T. delbrueckii_ received particular attention due to its ability to ferment maltose, produce ester compounds, and biotransform the monoterenoid flavor compounds of hops [14; 12; 15; 16]. In particular, _T. delbrueckii_ canimprove the amount of different fruity aromas, such as \(\beta\)-phenyl ethanol (\"rose\" flavors), n-propanol, iso-butanol, amyl alcohol (\"solvent brandy\" aroma), and ethyl acetate [17; 18; 19].  
[PERSON] et al. [6; 12] evaluated the use of _T delbrueckii_ for beer production, both pure and in mixed cultures with different _S. cerevisiae_ starter strains. _T. delbrueckii_ in mixed fermentation with different _S. cerevisiae_ starter strains showed different behavior and resulting in beers with distinctive flavors. Generally, the main aromatic compounds that were affected by _T. delbrueckii_ are some fruity esters. Furthermore, in mixed fermentation, _T. delbrueckii_ provided higher levels of higher alcohols, in contrast to data obtained in winemaking, where higher alcohols had lower levels. Moreover, beers obtained with _T. delbrueckii_ pure cultures were characterized by a distinctive analytical, aromatic profile, and a low alcohol content (2.66% _v/v_) [12].  
[PERSON] et al. [16] investigated different _T. delbrueckii_ strains coming from different habitats. One strain was able to produce a fruity and floral aroma (\(\beta\)-phenyl ethanol) and amyl alcohols. Furthermore, two strains were found to be suitable for producing low-alcohol beer owing to their inability to ferment maltose and maltotriose but still produced good flavor. However, investigation into the use of non-conventional yeasts in the brewing process has been performed at a laboratory scale or at a pilot scale while validation trials are lacking at the industrial level, which would give a more accurate assessment of their brewing ability. For this reason and based on the results of previous investigations [6; 12] in this study, the contribution of _T. delbreuckii_ in mixed fermentation with _S. cerevisiae_ starter strain at inoculum ratio 1:20 was assessed at the microbrewery plant. The effect of this non-conventional yeast in mixed fermentation on the evolution of biomass and aroma profile as well as on the final beer composition was evaluated. The sensorial profile of the final beers was also tested.