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In 2022, Dusart et al. analyzed and compared flavor compounds of a bottle of 2015 Rodenbach Vintage (unblended oak aged Old Ale), a 2021 bottle of Rodenbach Grand Cru (blend of 1/3 young beer and 2/3 oak aged Old Ale), and a 2021 bottle of Liefmans Goudenband (stainless steel aged Old Ale blended with young beer). They reported that iso-alpha acid content was low in all three bottles, as expected. Specifically, the Rodenbach Vintage had no detectable iso-cohumulone and only 0.25 mg/L iso-humulone. The Rodenbach Grand Cru had around 1.2 mg/L each of iso-cohumulone/iso-humulone, and the Liefmans had around half that amount. Interestingly, the Liefmans bottle had around 1.5 mg/L of tetrahydroisohumulones, eluding the use of tetra iso-alpha hop extract, which has been found to increase head retention in sour beers <ref name="Dusart_2022" />.
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 heating barrels (vanillan, acetovanillone, syringalde-hyde, and eugenol). Surprisingly, the Liefmans bottle also had some of these phenols (vanillan and lactones), indicating that perhaps some of these came from the specialty malts used <ref name="Dusart_2022" />.
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