Performance of Wild Non-Conventional Yeasts in Fermentation of Word Based on Different Mal Extracts to Select Novel Starters for Low-Alcohol Beers  
[PERSON]  
1 Scuola di Scienze Agraie, Forestali, Alimentari ed Ambientali, Universita degli Studi della Basilicata, 85100 Potenza, Italy; [EMAIL_ADDRESS]  
flavours in these beers. In fact, the fermentative process plays a key role in determining the characteristics of the final product, as yeast metabolism affects not only the ethanol yield from the sugar substrate but also aroma composition. The yeast strains chosen for word fermentation and beer conditioning play a fundamental role in beer quality, as the production of numerous aromatic compounds is strain-dependent [1,2]. Pyruvate produced by yeasts during glycolysis provides carbon skeletons for the synthesis of several aroma compounds, such as esters and higher alcohols [3]. Furthermore, yeast's enzymatic activities can modify the phenolic composition of word, determining the release of volatile organic compounds. As a consequence, the use of non-conventional yeasts might allow the production of low-alcohol beers with peculiar aromatic traits. Therefore, management of fermentation by using novel yeast starters represents the widest space in which the brewer can easily operate for beer diversification. This is very attractive for the current beer market, which is seeking to extend their product portfolio to satisfy consumer demand, always looking for new styles of beer. Furthermore, this approach might be very useful for small and craft breweries. In these production plants, changing the yeast is a feasible modification compared with the substantial equipment investment necessary for the application of physical methods for dealcoholisation. In recent years, the selection of non-conventional yeasts for the production of low-alcohol beers has expanded. Although these yeasts have been conventionally considered detrimental for alcoholic beverages, as they can negatively affect sensorial characteristics of the final products [4, 5, 6, 7, 8], the set-up of a suitable selection protocol and the accurate management of fermentative process can contribute to the production of fermented beverages with innovative aromatic characteristics that fulfil the modern consumer's expectations of products with novel aromatic tastes obtained without the use of chemical additives. Numerous studies report the use of non-_Saccharomyces_ yeasts as bio-flavouring agents in wine production [9, 10, 11] but, in recent years, studies describing the use of these yeasts for brewing processes have become available [7, 12, 13]. As non-conventional yeasts generally are characterised by lower ethanol yield than _Saccharomyces_, they are frequently used in co-fermentation or in sequential fermentation with classical _Saccharomyces_ brewing yeasts, but some studies report the use of these yeasts as pure starter cultures for producing low-alcohol (0.5-1.2% \(v/v\)) or even alcohol-free (<0.5% \(v/v\)) beers, which are increasingly demanded beverages [14]. Strains belonging to _Bretanomyces_ or _Dekera_ genera are among the most investigated non-conventional yeasts for beer fermentation [15]. Most of these yeasts are able to ferment the main sugars present in word; furthermore, these yeasts hydrolyse glucoside-bound monoterpenes present in the hops, liberating monoterpenes such as linalool that are the key aroma substances from hops [16]. However, other yeasts have recently been used in the brewing process. For instance, _Saccharomyces_ ludwigii_[17] and _Pichia kluyveri_[18], characterised by an inefficient fermentation of maltose and maltotriose, were successfully used to produce alcohol-free beers with rich flavour. _Toruslugora delbrueckii_ has been proposed for a long time as a mixed culture in winemaking for its positive influence on wine aroma, whereas in the last few years, this species has also been used for ethanol reduction both in wine and beer [19, 20, 21]. The studies investigating the contributions of _T.