Why aging is so different in dry-hopped beers: Fate of their bitterness, flavors, and polyphenols after two years of storage
(2019) 2019 ASBC Meeting — Location: New Orleans, USA (24.June.2019)
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- Abstract
- Dry-hopped (DH) beers have been rising in popularity all over the world in the last decade, partially due to the emergence of a large panel of interesting new hop varieties. Discriminant polyfunctional thiols and terpenols, found well above their sensorial threshold, give a unique profile to these beers, directly linked to the way the dry hopping was applied (hop cultivar, temperature, time, yeast, specific process…). Humulinones are known to impart (up to 28 % for Belgian DH beers) a particular bitterness to them while hop polyphenols reduce their colloidal stability. The aim of the present work is to assess why these beers behave so differently through ageing. 21 DH Belgian beers, including the famous DH trappist already on the market since 1931, have been followed during two years of storage. Besides basic parameters (extracts, alcohol content, color, pH…), our study focused on bitterness (official methods and newly developed HPLC assays more adapted for DH beers), flavors (Solvent Assisted Flavor Evaporation – SAFE and p-hydroxymercuribenzoic acid – pHMB extractions) and polyphenols (colloidal stability measurements and newly developed NP and RP-HPLC-ESI(-)-MS/MS methods). As expected, spectrophotometric bitterness and isohumulones concentrations strongly decreased (up to 16.4 ºBU and 18.2 mg/L isohumulones). trans-Isohumulones revealed much more impacted (up to 92 %) than its cis isomer. A very interesting data was the complete degradation, after two years of storage, of humulones and humulinones, by opposition to hulupones and tetrahydroisohumulones. The sensorial properties of the derived products were investigated. Aroma instability of DH beers is obviously the biggest hurdle for all brewers producing DH beers. Most of the so-pleasant polyfunctional thiols, including 3-sulfanylhexanol and 3-sulfanyl-4-methylpentanol, revealed completely degraded after ageing while half of the fruity ethyl hexanoate and isoamyl acetate disappeared in the same time. Linalool, usually found at very high levels in fresh beers (up to 498 μg/L for our samples), was the only terpenoid which remained above its sensorial threshold after ageing. Its loss correlated to that of geraniol and methyl geranate. Total polyphenols, determined by global methods, remained stable after two years, although drastic chemical transformations occurred among flavanoids. (+)-Catechin, (-)-epicatechin, procyanidins B3, B2, A2, C2 and C1 strongly dropped through ageing, with formation of new bridged compounds responsible of color and colloidal instability. This first review of DH beer ageing will be concluded by original proposals allowing to improve hop aroma, bitterness and colloidal stability of these beers. Their impact will be discussed in relation to other usual stale flavors, including trans-2-nonenal (cardboard), 3-sulfanyl-3-methylbutyl formate (ribes) and sotolon (madeira).
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Citations
Silva Guimarães Ferreira, C. A., & Collin, S. (2019). Why aging is so different in dry-hopped beers: Fate of their bitterness, flavors, and polyphenols after two years of storage. 2019 ASBC Meeting, New Orleans, USA. https://hdl.handle.net/2078.5/109671