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→Rodenbach vs Liefmans Analysis
The phenols 4-ethylguaiacol (4EG) and 4-ethylphenol (4EP) were found in the range of 54-385 µg/l, with the Rodenbach Vintage (unblended Old Ale) having the highest amounts. These levels were still less than typical lambic/gueuze levels. The 4EG levels in Liefmans was only 54 µg/l, compared to the 236 µg/l in Rodenbach Grand Cru and 384 µg/l in Rodenbach Vintage. Liefmans had a fairly high level of 4EP (123 µg/l), but it was still below the flavor threshold of 150 µg/l. In addition, Liefmans had high levels of of 4-vinyl precursors, indicating that ''Brettanomyces'' is not present during the Liefmans brewing process. The scientists suggested that the detected 4EP came from the small amount of torrefied malt used in the Liefmans brewing process, which has been shown to produce small amounts of 4EP <ref name="Dusart_2022" /><ref>[https://pubs.acs.org/doi/10.1021/jf5015654 Scholtes, C.; Nizet, S.; Collin, S. Guaiacol and 4-Methylphenol as Specific Markers of Torrefied Malts. Fate of Volatile Phenols in Special Beers through Aging. J. Agric. Food Chem. 2014, 62, 9522–9528. DOI: 10.1021/jf5015654.]</ref>. Both Rodenbach beers had detectable lactones and other phenols associated with toasting barrels (vanillin, acetovanillone, syringalde-
hyde, and eugenol). Surprisingly, the Liefmans bottle also had some of these phenols (vanillin and lactones), indicating that perhaps some of these came from the specialty malts used <ref name="Dusart_2022" />.
Esters and alcohols were also measured in all three bottles by the scientists. Ethyl acetate, which is a byproduct of yeast fermentation (especially ''[[Brettanomyces]]'' fermentation) and has an odor threshold of 30 mg/L in beer, was considerably high in all three beers: Liefmans had around 100 mg/L, Rodenbach Grand Cru had around 132 mg/L, and Rodenbach Vintage had 237 mg/L. By comparison, clean ales have around 8-48 mg/L, pasteurized gueuzes have around 33-67 mg/L, and unpasteurized gueuzes have around 61-167 mg/L. Noticeably, the Rodenbach Vintage had considerably high ethyl acetate, even when compared to gueuze. As expected, isoamyl acetate was below odor threshold (1.2 mg/L) in the Rodenbach beers, but above odor threshold in the Liefmans (1.73 mg/L). Isoamyl alcohol was above odor threshold in all three beers. The ester 2-phenylethyl acetate was also below threshold in the Rodenbach beers but not the Liefmans, while its alcohol precursor was high in the Rodenbach. Both esters, isoamyl acetate and 2-phenylethyl acetate, are known to be degraded into ethyl acetate by ''Brettanomyces''. Ethyl hexanoate, ethyl octanoate, and ethyl decanoate esters had levels similar to typical ''Saccharomyces'' fermentations. The Liefmans bottle reached the odor threshold level for oct-1-en-3-ol, which has an earthy/mushroom/musty odor and is considered an off flavor in beer <ref name="Dusart_2022" />.
The short chain fatty acids [[isovaleric acid]] and hexanoic acid were also measured. Isovaleric acid can be produced by ''Brettanomyces''. It can also be produced by the oxidation of hop acids. The levels of isovaleric acid in the Liefmans and Rodenbach Grand Cru was around the same as it is for regular ales (0.98 mg/L and 0.96 mg/L, while the Rodenbach Vintage reached the odor threshold (1.5 mg/L in beer) of isovaleric acid at 1.53 mg/L. By comparison, gueuze has been measured to have up to 2-3 mg/L of isovaleric acid. Hexanoic acid (also known as caproic acid, and is fatty/sweaty/cheesy/goaty), however, was found at much higher levels in all three beers. At an odor threshold of 8 mg/L in beer, Liefmans measured 10 mg/L, Rodenbach Grand Cru measured 11.26 mg/L, and Rodenbach Vintage measured 11.8 mg/L <ref name="Dusart_2022" />. Pentanoic, octanoic, and decnaoic acids were found below odor threshold <ref name="Dusart_2022" />.
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