Chemometric analysis of the volatile fraction evolution of Portuguese beer under shelf storage conditions Ricardo Rendall a , Marco S. Reis a, ⁎, Ana Cristina Pereira a , Cristina Pestana b , Vanda Pereira c,d , José Carlos Marques c,d a CIEPQPF, Department of Chemical Engineering, University of Coimbra, Rua Sílvio Lima, 3030-790, Coimbra, Portugal b Empresa de Cervejas da Madeira, Parque Empresarial Zona Oeste, 9304-003 Câmara de Lobos, Portugal c Centre of Exact Sciences and Engineering, University of Madeira, Campus da Penteada, 9000-390 Funchal, Portugal d Institute of Nanostructures, Nanomodelling and Nanofabrication (I3N), University of Aveiro, Aveiro, Portugal abstract article info Article history: Received 17 September 2014 Received in revised form 24 November 2014 Accepted 24 January 2015 Available online 3 February 2015 Keywords: Lager beer Volatile profile Chemometrics Principal component analysis Clustering Variables' contributions In this work we present a multivariate statistical analysis of the evolution of the volatile fraction of Portuguese beer over an extended period of 1 year under standard shelf storage conditions, using gas chromatography coupled with mass spectrometry (GC–MS). A systematic methodology is proposed for detecting the onset of meaningful changes in chemical composition during shelf storage and to monitor its evolution along time. We also put forward and discuss chemometric procedures for analyzing the contributions of different chemical com- ponents in the definition of dynamic ageing trends. In summary, the chemometric analysis reveals that the chem- ical composition of beer presents a statistically meaningful deviation from the reference scenario after a period of 7 months, although the deviation trend has its onset during the 6th month. The analysis performed also under- lines the limitations of current variable contribution methods, and an alternative procedure was proposed based on the analysis in the original domain which finally led to a consistent and interpretable clustering structure of the volatile fraction compounds. Esters and higher alcohol compounds stand up on a cluster arrangement sug- gesting that their strict control can effectively point out meaningful changes on beer aroma. Organic acids, name- ly caprylic, capric and acetic acids can also be very helpful in that sense. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Brewery industry has been well-succeeded in dealing with a wide variety of relevant quality issues in its products. Quality aspects related with beer appearance and safety, namely colloidal stability, haze forma- tion or microbiological spoilage, are now considered to be completely under control. Currently, the most important quality parameter and the shelf-life-limiting quality aspect is beer flavor [1–4] and efforts have been conducted towards maximizing and predicting beer shelf life taking into account flavor information. Several compounds have been pointed out as key agents of beer sensory changes and suggested as deterioration markers during ageing, in particular diacetyl [5], acetaldehyde and ethyl acetate [6], (E)-2-nonenal [7], Iso-α-acids [8], riboflavin and amino acids [9] and 5-hydroxymethylfurfural [10]. However, the evaluation of beer shelf life should be more comprehensive and take into account the heteroge- neity of chemical volatile groups presented in beer, which can either individually or simultaneously, influence the beer stale flavor in a synergistic or antagonistic sense [11]. Furthermore, beer aroma is also an important aspect in customer preferences and loyalty, since the typ- ical beer consumer, once he/she has approved and selected a given brand, expects the same “degree of excellence” (i.e., quality) from the product on future experiences [6,12–15]. Aware of the importance of aroma evolution during ageing, brewers and the scientific community have been developing approaches to eval- uate the overall beer aroma quality as well as strategies to verify the ac- complishment of expected attributes in the final product. Electronic sensors have deserved special attention in that sense. A number of pa- pers have proposed the use of electronic tongue devices for quality con- trol, in particular regarding the prediction of beer sensory attributes frequently evaluated according to the brewers' panel list [16–19]. Re- sults achieved in these works suggest that e-tongue can be used as a fast screening tool to check quality control parameters in a routine way. Electronic nose systems have also been tested to evaluate aroma fingerprint changes in beer during the ageing process. M. Ghasemi- Varnamkhasti et al. reviewed the last applications of e-nose in brewery applied to quality assessment [20], reporting applications for hop's quality assessment [21], on-line process control [22], monitoring the odor and taste of active compounds [23] and as a brand authenticity checking tool [24,25]. All works reported in this review take advantage Chemometrics and Intelligent Laboratory Systems 142 (2015) 131–142 ⁎ Corresponding author. Tel.: +351 239 798 700; fax: +351 239 798 703. E-mail address: marco@eq.uc.pt (M.S. Reis). http://dx.doi.org/10.1016/j.chemolab.2015.01.015 0169-7439/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Chemometrics and Intelligent Laboratory Systems journal homepage: www.elsevier.com/locate/chemolab