Recipe, volatiles profile, sensory analysis, physico-chemical and microbial characterization of acidic beers from both sourdough yeasts and lactic acid bacteria

Abstract

The study focused on the recipe optimization, production, physico-chemical and sensory characterization of sourdough beer and their comparison to commercial beers. For the first time the whole sourdough microbiota (not only yeasts but also lactic acid bacteria) was used as a starter. The microbiota was not isolated, the starter was a practical suspension of sourdough in water. The changes of gravity, pH, fermentation rate, and microbial counts during fermentation were rationalized on the basis of microbial metabolism. The initial prevalence of lactic acid bacteria evolves to a predominance of yeasts with a minimum pH. The reduction of gravity and pH is correlated to the oxidative sugar consumption and production of organic acids and carbon dioxide. The samples’ volatile profile, crucial from a commercial point of view, was described. The most abundant volatiles are esters and alcohols. Ketones, aldehydes, and hydrocarbons are present to a lower extent. Vicinal diketones, responsible for beer off-flavor, and hydrocarbons are only present in sourdough samples but not in the corresponding beer samples or in commercial beer. A comparison between the volatile fingerprints of an acidic beer and that of the corresponding sourdough was performed. The former is simpler that the latter. Acidic beers are characterized by the presence of ethyl butanoate and ethyl decanoate. A beer judge described beer sensory attributes. Principal component analysis and clustering analysis enabled the discrimination among sourdough, acidic beer and commercial beer. The industrial scale-up of this process is desirable because there is an increasing worldwide consumption of specialty beer.