Special beer aging : contribution of oxidation related compounds and roasted-like phenols

Since three decades, scientists have produced high amounts of literature on lager beer aging. Yet, our knowledge on top-fermentation beers behavior remains scarce. We started this study by the establishment of an overall picture of a panel of Belgian special beers. Esters, bringing nice freshness and fruity characters revealed quite stable in most beers, even after 12 months whereas a large variability of short chain fatty acid profiles emerged. Only isovaleric acid was found above its sensorial threshold, even after 2 years of aging. Study of theaspirane and sotolon, two unknown aromas for brewers although particularly relevant in oxidized beverages, were also investigated. For sotolon which emerged as responsible of the Madeira off-flavor found in some aged special beers, the key role of acetaldehyde, ascorbic acid and acetoin were highlighted. We also evidenced for the first time 6 interesting theaspirane oxidation derived compounds. Two of them revealed flavor-active: 4-hydroxy-7,8-dihydro-β-ionone exhaling a grenadine aroma and dihydrodehydro-β-ionone, with a nice Sauternes-like aroma (found under free and glucosilated forms in hop). The last part of the thesis was devoted to the torrefied character of Belgian brown beers through aging. Guaiacol and 4-methylphenol, two new markers of the use of torrefied malts, were found still more concentrated after aging, while vanillin displayed different patterns according to the type of beer. Vanillin, guaiacol and 4-methylphenol glucosides were evidenced for the first time in dark malts.