Microbiota and metabolites of aged bottled gueuze beers converge to the same composition

• Aging of gueuze beers has an impact on the microbiota and metabolites.
• Yeast could be isolated from all bottles, but bacteria disappeared.
• Lactic acid and ethyl lactate were produced during aging.
• Isoamyl acetate and ethyl decanoate concentrations decreased during aging.
• Considerable bottle-to-bottle variations were found.

Gueuze beers are prepared by mixing young and old lambic beers and are bottle-refermented spontaneously for aging. The present study analyzed the microbiota and metabolites present in gueuze beers that were aged between a few months and up to 17 years. Yeasts were cultivated from all beers sampled, but bacteria could not be grown from beers older than 5 years. Lactic acid and ethyl lactate concentrations increased steadily during aging, whereas ethanol concentrations remained constant. The concentrations of isoamyl acetate and ethyl decanoate decreased during the aging process. Hence, ethyl lactate and ethyl decanoate can be considered as positive and negative gueuze beer-aging metabolite biomarkers, respectively. Nevertheless, considerable bottle-to-bottle variation in the metabolite profiles was found, which hindered the generalization of the effects seen during the aging of the gueuze beers examined, but which illustrated the unique character of the lambic beers. The present results further indicate that gueuze beers are preferably aged for less than 10 years.