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Theses Year : 2020

On the Origins and Formation Kinetics of Worty Flavours in Alcohol-Free Beers

Sur les origines et cinétique de formation des arômes à moût de bière dans la bière sans alcool

Abstract

The interest of consumers towards alcohol-free beer (AFB) has increased over the last few years due to several motivations. However, some of them, such as those brewed by cold contact fermentation (CCF) show a characteristic aroma reminiscent of wort or malt, lacking the appreciated fruity flavour of their alcoholic counterparts. From the current literature, the Strecker aldehydes methional, 2- and 3-methylbutanal are responsible for this aroma. The aim of this PhD project was to identify the role of odour-active compounds in AFB and their contribution to the worty character, as well as to study the formation kinetics of them during malt kilning. By means of the sensomic approach, five key aroma compounds were identified, among 27 odour-active compounds. These were methional (boiled potato-like aroma), 3-methylbutanal (cocoa-like), (E)-β-damascenone (apple, jam-like), 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone (curry, spicy-like), and phenylacetaldehyde (floral, honey-like). As a part of the sensomic method, perception thresholds of the odour-active compounds were determined in an AFB-like matrix. Differences were observed between our threshold values, both ortho- and retronasal, and the values from the literature in water and ethanol/water mixtures. Moreover, the calculation method employed (best estimate threshold BET or logistic regression) and the presence of false positives had a significant impact on the final results. In the next part of the project, the formation of (E)-β-damascenone and Strecker aldehydes during malt kilning (isothermal curing stage at 65, 78 or 90 °C) was investigated. The former increased over time in malts kilned at 78 and 90 °C, whilst at 65 °C the trend was not very clear. During mashing and wort boiling, the amount of (E)-β-damascenone was affected by a compromise between formation and degradation/evaporation. The formation of five Strecker aldehydes (the four mentioned above and 2-methylpropanal) was monitored during the curing stage of malt kilning too. These compounds are formed during thermal processes by the Maillard reaction between reducing sugars and amino acids. Multi-response kinetic modelling was used to fit the analytical results to a mechanistic mathematical model. The model developed showed the importance of the formation of two intermediate compounds in the reaction of glucose and amino acids. The first group of intermediates was Amadori rearrangement products (ARP), whereas the second was a pool of short chain dicarbonyls, such as glyoxal and methylglyoxal, that were not determined analytically. The results from the kinetic parameters demonstrated the high sensitivity of the degradation of ARP to changes in temperature because of its high activation energy. The outcomes from this PhD may have a great importance for brewers and brewing scientists. The understanding of the role of flavour compounds in AFB is the starting point to design mitigation strategies for the formation of worty off-flavours and thus improve the beer’s organoleptic characteristics and consumer acceptability.
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Dates and versions

tel-03839875 , version 1 (04-11-2022)

Identifiers

  • HAL Id : tel-03839875 , version 1

Cite

José A. Piornos. On the Origins and Formation Kinetics of Worty Flavours in Alcohol-Free Beers. Food and Nutrition. University of Reading, 2020. English. ⟨NNT : ⟩. ⟨tel-03839875⟩

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