Influence of pH and ageing on beer organoleptic properties. A sensory analysis based on AEDA data Christine Guyot-Declerck a , Nancy Franc ßois b , Christian Ritter b , Bernadette Govaerts b , Sonia Collin a, * a Universit e catholique de Louvain, Unit e de Brasserie et des Industries Alimentaires, Croix du Sud 2, Boite 7, B-1348 Louvain-la-Neuve, Belgium b Universit e catholique de Louvain, Institut de statistique, Voie du Roman Pays 20, B-1348 Louvain-la-Neuve, Belgium Received 17 November 2003; received in revised form 5 February 2004; accepted 19 April 2004 Available online 20 June 2004 Abstract Brewers need to know how ageing affects the organoleptic properties of beer. This paper describes sensory assessments of aroma changes in lager beer subjected to accelerated staling (5 days at 40 °C) at different pH values (4.2 and 4.6), according to a new methodfortrainingpanellists,basedonAEDAresults.Itshows,for10keycompoundswhoseconcentrationsareknowntoincrease during staling, how modifications in pH affect ageing and perception thereof. In agreement with the AEDA results, ‘‘dimethyltrisulphide’’-, ‘‘trans-2-nonenal’’- and ‘‘methional’’-like perceptions increased significantly as a result of ageing in regular pH 4.2 lager beers. A higher pH led to a smaller age-related intensity increase in the ‘‘cardboard’’ note (‘‘trans-2-nonenal’’-like). It also enhanced the ‘‘coconut’’ character (‘‘c-nonalactone’’-like) but did not change the age-related intensification of the ‘‘cabbage’’ note (‘‘dimethyltrisulphide’’-like). Perception of the remaining six compounds (‘‘furaneol’’-, ‘‘ethyl butyrate’’-, ‘‘2-methoxypyrazine’’-, ‘‘acetylpyrazine’’-, ‘‘b-damascenone’’- and ‘‘ethyl cinnamate’’-like) did not evolve with ageing or pH. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Beer; pH; Ageing; Sensory analysis 1. Introduction Oneofthemainconcernsofbrewersistopreservethe organoleptic stability of beer during ageing. A key fac- tor influencing beer ageing and its stability is pH (Bamforth, 2001). From a sensory standpoint, if the pH of fresh beer decreases below 4.0, sharp, acid, bitter, and drying effects increase rapidly in intensity, with a markedly enhanced metallic after-palate for pH values below 3.7. On the other hand, above 4.0, palate effects relate to increased mouth-coating, with higher scores for biscuity and toasted characters, and even soapy and caustic notes if the pH rises above 4.4 (Taylor, 1990). Increasing the pH proved to be an interesting way to reduce formation of trans-2-nonenal, responsible for an unpleasant cardboard note in aged beer. Retention of trans-2-nonenal by amino acids and proteins during ageing is enhanced at higher pH, explaining why a lesser cardboard flavour is perceived (Lermusieau, No€ el, Li egeois, & Collin, 1999; No€ el et al., 1999). A higher pH also makes it possible to control the apparition of b-damascenone (cooked apple-like) (Che- vance, Guyot-Declerck, Dupont, & Collin, 2002) and dimethyltrisulphide (cabbage-like) through ageing. Unfortunately, methional (cooked potato-like) produc- tion is enhanced under these conditions (Gijs, Chevance, Jerkovic, & Collin, 2002). To highlight the overall flavour consequences of pH modification on beer ageing, sensory analysis (and especially Quantitative Descriptive Analysis) appears as aprimetechniquebasedonacomparativedescriptionof the organoleptic properties of several products (Stone, Sidel, Oliver, Woolsey, & Singleton, 1974). This ap- proach requires two steps: first a vocabulary genera- tion step, which involves obtaining a consensual descriptor list from the panel members, and then a quantitative intensity assessment of each selected term * Corresponding author. Tel.: +32-10-47-29-13; fax: +32-10-47-21- 78. E-mail address: collin@inbr.ucl.ac.be (S. Collin). 0950-3293/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodqual.2004.04.007 Food Quality and Preference 16 (2005) 157–162 www.elsevier.com/locate/foodqual