Diacetyl is a vicinal dichetone, which is formed as a by-product of valine metabolism by yeast in alcoholic fermentation, and contributes to the aromatic profile of many fermented products, including low fermentation beers. Its typical butter flavor is considered an "off flavor" in lager style beers and its removal has a great impact on the time and energy expenditure in breweries. Furthermore, in some cases it may also indicate microbial contamination when hygiene standards do not comply. The process of reduction of diacetyl by yeast is not well understood as that of formation, but depends on factors such as physiological conditions, cell membrane composition, temperature and pH. Several strategies are applied to improve the overall efficiency of the production system, which are based on minimising the formation of diacetyl in green beer and accelerating the reduction of diacetyl to 2,3-butanediol. This paper highlights the correlation between the reduction of diacetyl in fermentation and the number of generations of yeast, verifying the effective influence on the final quality of beer. In this regard, a study was carried out in collaboration with the Birra Peroni (PD) factory, in which several generations and strains of yeast (S. pastorianus) were exploited. The fermentation of brews has been analyzed and compared with the fermentations of other brews, present in the archive of Birra Peroni, and with the results of the study of "The effect of yeast generations on fermentation, maturation and volatile compounds of beer" by Kucharczyk K. et al. (2020). The experimental test confirmed that the third generation strains have a better performance, expressed in days, in the reduction of diacetyl, since the adaptation of yeast to must takes place in shorter times (reducing the "lag phase"). Serial re-inoculus and the use of third generation yeast seem to be a natural, simple and economical strategy for diacetyl control and yeast management in beer production.
Il diacetile è un dichetone vicinale, che si forma come sottoprodotto del metabolismo della valina da parte del lievito nella fermentazione alcolica, e contribuisce al profilo aromatico di molti prodotti fermentati, tra cui le birre a bassa fermentazione. Il suo tipico sapore di burro è considerato un “off flavor” nelle birre in stile lager e la sua rimozione ha un grande impatto sul tempo e sul dispendio di energia nei birrifici. In alcuni casi può anche indicare una contaminazione microbica quando gli standard igienici non sono conformi. Il processo di riduzione del diacetile da parte del lievito non è ben compreso come quello di formazione, ma dipende da fattori quali le condizioni fisiologiche, la composizione della membrana cellulare, la temperatura e il pH. Per migliorare l’efficienza complessiva del sistema di produzione si applicano diverse strategie, tra cui una minore formazione di diacetile nella birra verde e l’incremento della velocità di riduzione del diacetile in 2,3-butandiolo. Il presente elaborato mette in luce la correlazione tra l’abbattimento del diacetile in fermentazione e il numero di generazioni del lievito, verificando l’effettiva influenza sulla qualità finale della birra. A tal proposito è stato condotto uno studio in collaborazione con lo stabilimento di Birra Peroni (PD), in cui sono state sfruttate diverse generazioni e ceppi di lievito (S. pastorianus). La fermentazione delle cotte è stata analizzata e comparata con le cartelle di fermentazioni di altre cotte, presenti nell’archivio di Birra Peroni, e con i risultati dello studio di “The effect of yeast generations on fermentation, maturation and volatile compounds of beer” di Kucharczyk K. et al. (2020). La prova sperimentale ha confermato che i ceppi di terza generazione hanno una migliore performance, espressa in giorni, nella riduzione del diacetile, poiché l’adattamento del lievito al mosto avviene in tempistiche più brevi (riducendo la “lag phase”). Il re-inoculo seriale e l’uso di lieviti di terza generazione sembrano essere una strategia naturale, semplice ed economica per il controllo del diacetile e la gestione del lievito nella produzione della birra.
Produzione di diacetile durante la fermentazione alcolica: l’effetto della gestione del lievito nel processo di birrificazione
FAMOSO, TERESA
2023/2024
Abstract
Diacetyl is a vicinal dichetone, which is formed as a by-product of valine metabolism by yeast in alcoholic fermentation, and contributes to the aromatic profile of many fermented products, including low fermentation beers. Its typical butter flavor is considered an "off flavor" in lager style beers and its removal has a great impact on the time and energy expenditure in breweries. Furthermore, in some cases it may also indicate microbial contamination when hygiene standards do not comply. The process of reduction of diacetyl by yeast is not well understood as that of formation, but depends on factors such as physiological conditions, cell membrane composition, temperature and pH. Several strategies are applied to improve the overall efficiency of the production system, which are based on minimising the formation of diacetyl in green beer and accelerating the reduction of diacetyl to 2,3-butanediol. This paper highlights the correlation between the reduction of diacetyl in fermentation and the number of generations of yeast, verifying the effective influence on the final quality of beer. In this regard, a study was carried out in collaboration with the Birra Peroni (PD) factory, in which several generations and strains of yeast (S. pastorianus) were exploited. The fermentation of brews has been analyzed and compared with the fermentations of other brews, present in the archive of Birra Peroni, and with the results of the study of "The effect of yeast generations on fermentation, maturation and volatile compounds of beer" by Kucharczyk K. et al. (2020). The experimental test confirmed that the third generation strains have a better performance, expressed in days, in the reduction of diacetyl, since the adaptation of yeast to must takes place in shorter times (reducing the "lag phase"). Serial re-inoculus and the use of third generation yeast seem to be a natural, simple and economical strategy for diacetyl control and yeast management in beer production.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/67804