Daan Saison

Instrumental measurement of beer taste attributes using an electronic tongue

The present study deals with the evaluation of the electronic tongue multisensor system as an analytical tool for the rapid assessment of taste and flavour of beer. Fifty samples of Belgian and Dutch beers of different types (lager beers, ales, wheat beers, etc.), which were characterized with respect to the sensory properties, were measured using the electronic tongue (ET) based on potentiometric chemical sensors developed in Laboratory of Chemical Sensors of St. Petersburg University. The analysis of the sensory data and the calculation of the compromise average scores was made using STATIS. The beer samples were discriminated using both sensory panel and ET data based on PCA, and both data sets were compared using Canonical Correlation Analysis. The ET data were related to the sensory beer attributes using Partial Least Square regression for each attribute separately. Validation was done based on a test set comprising one-third of all samples. The ET was capable of predicting with good precision 20 sensory attributes of beer including such as bitter, sweet, sour, fruity, caramel, artificial, burnt, intensity and body.

Optimisation of a complete method for the analysis of volatiles involved in the flavour stability of beer by solid-phase microextraction in combination with gas chromatography and mass spectrometry

Headspace solid-phase microextraction combined with gas chromatography and mass spectrometry was used for the quantification of 32 volatiles which represent the typical chemical reactions that can occur during beer ageing. Detection was accomplished by employing on-fibre derivatisation using o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and normal HS-SPME extraction. The procedures were optimised for SPME fibre selection, PFBHA loading temperature and time, extraction temperature and time, and effect of salt addition. Interference of matrix effects was overcome by calibrating according to the standard addition method and by using internal standards. Afterwards, the method was validated successfully and was applied to study the flavour stability of different beer types.

Determination of carbonyl compounds in beer by derivatisation and headspace solid-phase microextraction in combination with gas chromatography and mass spectrometry.

Headspace solid-phase microextraction (SPME) followed by gas chromatography and mass spectrometry was applied for quantification of 41 chemically diverse carbonyl compounds in beer. Therefore, in-solution derivatisation with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) combined with SPME was optimised for fibre selection, PFBHA concentration, extraction temperature and time and ionic strength. Afterwards, the method was calibrated and validated successfully and extraction efficiency was compared to sampling with on-fibre derivatisation. In-solution derivatisation enabled the detection of several compounds that were poorly extracted with on-fibre derivatisation such as 5-hydroxymethylfurfural, acrolein, hydroxyacetone, acetoin, glyoxal and methylglyoxal. Others, especially (E)-2-nonenal, were extracted better with on-fibre derivatisation.

Screening and evaluation of the glucoside hydrolase activity in Saccharomyces and Brettanomyces brewing yeasts

Aims:  The aim of this study was to select and examine Saccharomyces and Brettanomyces brewing yeasts for hydrolase activity towards glycosidically bound volatile compounds.

Decrease of Aged Beer Aroma by the Reducing Activity of Brewing Yeast

The flavor profile of beer is subject to changes during storage. Since, possibly, yeast has an influence on flavor stability, the aim of this study was to examine if there is a direct impact of brewing yeast on aged aroma. This was achieved by refermentation of aged beers. It was shown that several aged aroma notes, such as cardboard, ribes, Maillard and Madeira, were removed almost entirely by brewing yeast, independently of the yeast or the beer type. This was explained by the reduction of aldehydes, mainly (E)-2-nonenal, Strecker aldehydes, 5-hydroxymethylfurfural and diacetyl, to their corresponding alcohols. Furthermore, it became evident that the reducing capacity of brewing yeast is high, but that yeast strain and compound specific residual concentrations remained in the refermented beer independently of the initial concentration. Finally, it appeared that aldehydes were not only reduced but also formed during refermentation.

Contribution of monophenols to beer flavour based on flavour thresholds, interactions and recombination experiments

Although monophenols are known to contribute to the flavour of many foods and beverages, little is known about their influence on beer flavour. Therefore, the contribution of 11 monophenols to the overall beer flavour was studied by determining their flavour thresholds. Large differences in sensitivity were observed between individual tasters. Next, flavour interactions between monophenols were examined in nine binary mixtures, which showed that strong interactions like synergy and antagonism occur. Based on these results, the flavour contribution of the monophenols was estimated by calculating flavour units. These proved to be rather low for most of the studied monophenols. However, recombination experiments demonstrated that monophenols enriched beer flavour with spicy, smokey and vanilla flavour aspects. This showed how monophenols might influence overall flavour, even at sub-threshold concentrations.

Determination of volatile monophenols in beer using acetylation and headspace solid-phase microextraction in combination with gas chromatography and mass spectrometry

Monophenols are widely spread compounds contributing to the flavour of many foods and beverages. They are most likely present in beer, but so far, little is known about their influence on beer flavour. To quantify these monophenols in beer, we optimised a headspace solid-phase microextraction method coupled to gas chromatography-mass spectrometry. To improve their isolation from the beer matrix and their chromatographic properties, the monophenols were acetylated using acetic anhydride and KHCO(3) as derivatising agent and base catalyst, respectively. Derivatisation conditions were optimised with attention for the pH of the reaction medium. Additionally, different parameters affecting extraction efficiency were optimised, including fibre coating, extraction time and temperature and salt addition. Afterwards, we calibrated and validated the method successfully and applied it for the analysis of monophenols in beer samples.

Decrease of 4-Vinylguaiacol during Beer Aging and Formation of Apocynol and Vanillin in Beer

In this study the decrease of 4-vinylguaiacol (4VG) during beer aging was investigated and the products that arise from it were identified. Two compounds, vanillin and apocynol, were identified in beer model solutions after forced aging and in naturally aged beers by GC-MS and HPLC-ECD analyses. Both account for up to 85% of the decrease of 4VG. Only in the presence of substantial amounts of oxygen in the bottle headspace was vanillin detected. Apocynol [4-(1-hydroxyethyl)-2-methoxyphenol] was found to be the main degradation product, and its formation was shown to be highly dependent on the beer pH. Because both apocynol and vanillin have a clear vanilla-like aroma, the decrease of 4-vinylguaiacol during beer aging might impart a shift from a clove-like aroma in fresh specialty beers (such as wheat beers and other top-fermented blond or dark ales) to a sweeter, more vanilla-like flavor impression of aged specialty beers.

Release and Evaporation of Volatiles during Boiling of Unhopped Wort

The release and evaporation of volatile compounds was studied during boiling of wort. The observed parameters were boiling time, boiling intensity, wort pH, and wort density. The effect of every parameter was discussed and approached chemically, with an eye on beer-aging processes. The results indicated that pH highly influenced the release of flavor compounds and that the formation of Strecker aldehydes was linear with boiling time. However, because of evaporation of volatiles, information about the applied thermal load on wort is lost when using a volatile heat load indicator. The thiobarbituric acid (TBA) method, which includes the nonvolatile precursors of volatile aging compounds, proved to be a more reliable method to determine all kinds of heat load on wort. Finally, it was discussed how the obtained insights could help to understand the mechanism of beer aging.

Optimisation of specialty malt volatile analysis by headspace solid-phase microextraction in combination with gas chromatography and mass spectrometry.

The objective of this study was to develop a technique for analysing 14 flavour components, relevant for specialty malts. Therefore, a method was developed for the analysis of these components in dry ground malt using headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. A procedure was optimised for the optimal amount of sample, fibre selection, extraction temperature and extraction time. Afterwards, the method was calibrated and validated by the quantification of the specialty malt flavour components in a colour, a caramel and a roasted malt.