Volatile fingerprinting differentiates diverse-aged craft beers

Highlights

• Different ageing strategies led to distinct volatile fingerprints.

• Beers were separated in clusters relating production strategy with volatile composition.

• Wine volatiles were transferred to aged beers by barrel reuse.

• Volatile fingerprinting is a tool for dealing with sample heterogeneity in beer analysis.

Abstract

Beer ageing on wood is a complex and difficult to control process involving several reactions and compounds. Difficulties in understanding the underlying phenomena often lead to empirical and unpredictable processes and heterogeneous products. This work resorts to volatile fingerprinting along with multivariate analysis as tools to differentiate and highlight differences in beers derived from diverse production processes. Volatile composition of beers originating from barrel ageing processes and unaged beer were analyzed by GC-MS. The collected data was processed by principal component analysis, which allowed the evaluation of relations between samples and volatile compounds. Beers were distinguished by clusters comprising different groups of volatiles. Beer with the longest period in barrel was in the cluster with the most volatiles. Beer produced by resident barrel microbiota fermentation was characterized by presence of Brettanomyces sp. metabolites. Beer aged in barrel by a shorter time period showed characteristic content of ethyl esters and oak extractives. Beer produced in inox vat and beer fermented in barrel with pitching of S. cerevisiae appeared in the same cluster, relating with fermentative esters. Volatile fingerprinting was a viable approach to characterize and distinguish the analyzed beers, providing relevant information regarding the impact of production methodologies in volatile composition.

Introduction

Ageing of beverages in oak barrels is a common practice and is widely recognized for improving stability and organoleptic properties of the final product. During contact, several phenomena occur which impact beverage composition, namely the extraction of wood compounds, evaporation of beverage volatile compounds, oxidation of compounds in the beverage, and reaction between wood and beverage components (Mosedale & Puech, 1998). Extraction of volatiles from oak barrels depends mainly on wood extractible content, contact time, cellar conditions and beverage composition (Chira & Teissedre, 2014). Barrel usage is a crucial factor for ageing. The pool of extractable oak compounds is finite and the rate and amounts of compounds extracted diminish as the barrel is used in successive years (Wilkinson, Li, Grbin, & Warren, 2013). Furthermore, casks also retain compounds from the beverages aged in them, due to sorption of beverages components. As shown, oak wood retains compounds from the aged beverages, which can be transferred from one beverage to another through the reuse of the cask (Coelho, Domingues, Teixeira, Oliveira, & Tavares, 2019). Presence of lees in the cask can also take part on enhancing sensorial characteristics of alcoholic beverages, leading to higher body and aroma complexity as acknowledged in wine production (Del Barrio-Galán, Pérez-Magariño, & Ortega-Heras, 2011). Therefore, volatile composition of the aged beverage is influenced not only by the previously referred reactions occurring in the barrel but also by transference of compounds from one matrix to another, with the barrel posing as a vector for carrying such compounds and aromatic properties. Additionally, when envisaging beverages such as wine or beer, biological transformations occur during barrel ageing which furthermore modify chemical and sensory properties. Casks are often populated with microorganisms that alter significantly the beverage composition. Bacteria, such as Lactobacillus sp. and Enterobacter sp. and wild yeasts such as Brettanomyces sp., Debaryomyces sp. and Candida sp. can be found in wood and wine barrels with impact on beverage composition (Spitaels et al., 2014). Whilst mainly considered as spoilage organisms responsible for off-flavor production in wine, an increasing number of authors report that these endogenous microbes can add beneficial (or at least interesting) aromas that increase the flavor complexity of fermented beverages. On this field, Brettanomyces sp. strains are rising in importance, due to the ability to produce volatile compounds that enhance sensory properties of beer (Serra Colomer, Funch, & Forster, 2019). Several beer styles traditionally produced by fermentation in barrel rely on typical Brettanomyces sp. flavors such as seen for Lambic beers (Steensels et al., 2015) and Belgian red-brown acidic ales (Snauwaert et al., 2016).

With an increasing market which strives for innovative specialty products, mainly in craft beer, barrel ageing has been applied at great extent. Variables such as wood type and origin, presence of lees, resident barrel microbiota and ageing conditions lead to a large number of possible combinations to be performed. With such extent of variables to be manipulated and taking into account the multitude of compounds involved in beer sensory characteristics, ageing results are often unpredictable lead to heterogeneous products in regard to their chemical composition and sensory characteristics. In the case of wine, which has also complex composition, fingerprinting methodologies have been applied as omics tools for the discrimination, identification and quality control of dissimilar samples (Laaks, Letzel, Schmidt, & Jochmann, 2012) and for the investigation of the importance and effect of wine volatiles (González Álvarez, González-Barreiro, Cancho-Grande, & Simal-Gándara, 2011).

The aim of this work was the application and evaluation of volatile fingerprinting along with multivariate analysis as a tool to discriminate and characterize differences in barrel diverse-aged beers.