Session Chair:
Goran Matic (Western Europe Supply Chain Excellence and Innovation Director, Molson Coors, UK)
Formation of Desired Key Odorants in Wheat Beer – a Comparison with the Undesired Toxicologically Relevant Styrene
By Michael Granvogl and Valerian Kalb, Universität Hohenheim
The use of wheat and barley malts for wheat beer production introduces the so-called phenolic acids. During fermentation, these acids are transferred into the corresponding vinyl aromatics by top-fermenting yeasts. For ferulic and p-coumaric acid, decarboxylation results in the formation of the two key odorants 2-methoxy-4-vinylphenol and 4-vinylphenol, responsible for the typical, well-known clove-like and slightly phenolic wheat beer aroma. Unfortunately, this formation is accompanied by the release of the undesired and toxicologically relevant styrene (classified as possibly carcinogenic to humans (class 2B) by the “International Agency for Research on Cancer”) from cinnamic acid. Therefore, the desired and undesired volatile vinyl aromatics and the corresponding phenolic acid profiles of a large number of commercially available wheat beers were analyzed via stable isotope dilution analysis (SIDA) by means of HS-SPME GCxGC-ToF-MS and LC-MS/MS, respectively. Pale, unfiltered, alcohol reduced, light, and two dark wheat beers were analyzed to get knowledge on the impact of dealcoholization process, type of yeast, and roasting degree on the vinyl aromatic and phenolic acid pattern.
New kombucha with standardized microbial consortia
By Laurence Van Nedervelde et al., Institut Meurice
Kombucha is a traditional low-alcoholic beverage made from sweet tea and transformed by a microbial consortium (SCOBY) consisting of yeasts and acid bacteria. Considered as a niche beverage for decades, kombucha is now invading grocery stores, supermarkets, and cafés as an alternative to sodas. Its success is attributable to its low sugar content, its all-natural composition and the many health claims relayed by the scientific literature. This study aims to develop a standardized microbial consortium efficient for the production of kombucha. For this, we isolated and screened for the most suitable yeast and bacterial strains. In addition to the nature of the microorganisms constituting the SCOBY, different parameters influencing the taste and final characteristics of kombucha are investigated: the initial sugar concentration, the tea type, the proportion of each microbial partner within the SCOBY, the fermentation temperature, and the fermentation time. The results highlight the main impact of bacterial species on the organic acids profile and the secondary impact of yeast metabolism on the chemical composition of kombucha, via invertase and fermentative activities.
Bottle refermentation determines the quality of gueuze beers
By Dries Bongaerts et al., Vrije Universiteit Brussel
Lambic beer can be enjoyed as such but is usually a basis for other beers. An example is gueuze, a blend of young and old lambic beers, which is refermented in the bottle. To better understand the influence of storage time on the quality of gueuze, which is of interest for both consumers and producers, bottle refermentation was followed as a function of time. This was approached through novel microbiota and metabolite analysis techniques. Culture-dependent and -independent identification mapped the microbial species diversity and community dynamics. Metabolomics unravelled substrate consumption and metabolite production. The early bottle refermentation microbiota reflected that of the maturation phase of lambic beer production. However, the species diversity decreased over time and, after three months, mainly Brettanomyces occurred. The metabolites were mostly linked with this yeast metabolism, including an increase in several alcohols, ethyl acetate, and ethyl lactate. Other compounds linked with the typical Brett flavour slightly decreased during the first months of bottle refermentation but increased again after six months. These data can be used to optimize the storage time.
Ageing beer using the Solera Method
By Luis Miguel Barrera Arbelaez, Grupo Mahou-San Miguel
Application of the solera method to beer production. A solera is essentially a series of barrels containing an identical liquid of consecutive ages. In the case of sherry wine, the method consists of extracting a quantity of wine at intervals (25 to 50%) throughout the year, and then the barrel is refreshed with wine of the same style but a little younger. This is done because the younger wine will gradually take on the character of the older wine, and after several years, the wine in the barrel becomes practically indistinguishable from what it was before. The application of this method develops a dynamic maturation system whereby the products is transferred through a system of barrels of increasing age. For this experiment, we used a highly attenuated Saison style beer, with almost 10 degrees of alcohol and a Solera system of 8 sherry barrels. The system includes the Soleras – the oldest barrel or set of barrels – and the Criaderas or nurseries. The aim is to establish a robust methodology for the production of specialty beer and present the yearly evolution results (since 2018) using microbiological, chemical, and sensory analyses.