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Investigating the evolution of free staling aldehydes throughout the wort production process
M. Ditrych, W. Filipowska, G. De Rouck, B. Jaskula-Goiris, G. Aerts, M. L. Andersen and L. De Cooman

During aging, beer undergoes a variety of unfavourable chemical reactions, which lead to inevitable flavour deterioration. Especially in light lagers and Pilsner styles, many of the off-flavours are associated with the presence of the so-called staling aldehydes. However, the formation of these compounds is not fully understood until now. From the perspective of the brewing process, aldehydes may arise as a result of e.g. fatty acids oxidation, Strecker degradation of amino acids, Maillard reactions, etc. Aldehydes may also be released from the non-volatile precursor forms, the so-called bound state aldehydes. Therefore, to unravel another puzzle piece of beer flavour instability, we have monitored the free staling aldehydes throughout the process of wort production. Levels of 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, hexanal, furfural, methional, phenylacetaldehyde and trans-2-nonenal were quantified. High levels of aldehydes determined in malt and mashing-in samples indicate the malt as the major source of staling aldehydes introduced into the brewing process. Furthermore, a decrease in the levels of free aldehydes was observed over the entire process, with exception of furfural. The highest decrease was observed during boiling. On the other hand furfural increased, not only during boiling, but also during wort clarification. Finally, a relative increase in aldehydes was observed during sparging. In summary, this study identifies the most critical steps during wort production in relation to free aldehyde formation.

Descriptors: staling aldehydes, flavour instability, wort production

BrewingScience, 72 (January/February 2019), pp. 10-17