Impact of fermentable and non-fermentable sugars on oxidative processes during brewing, SO2 formation, palate fullness, and flavor stability

Technical Session 08: Sensory Session
Thomas Kunz, Technische Universität Berlin, Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany
Co-author(s): Torsten Seewald, Niklas Brandt, Christof Reinhardt, and Frank-Jürgen Methner, Technische Universität Berlin, Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany

ABSTRACT: The aim of this study was to investigate the influences of fermentable and commonly used unfermentable sugars, usually added during wort boiling to increase the beer’s palate fullness, on oxidative processes during wort boiling, the SO2 formation, palate fullness, flavor, and formation of specific aging compounds. The first results demonstrate that the increase of osmotic pressure by addition of non-fermentable sugars is responsible for higher SO2 formation during fermentation. Addition up to 2% prior to fermentation leads to a better palate fullness and higher concentration of antioxidant substances like SO2 without notable influence on flavor or sweetness directly after filling. Otherwise, a previous investigation showed that sugars behave differently at low pH than the generally known behavior described by Fehling, resulting in a sugar type specific influence on oxidative processes during brewing and beer storage. The newly developed “Chapon” method (MBAA 2011) demonstrates that at low pH (4.2), the strongest reducing potential results from isomaltulose followed by fructose, Vitalose®, and maltotriose. The low reduction potential of the so called “reducing sugar” glucose at low pH can be explained by the inhibited formation of the open-chain aldehyde structure. In contrast, fructose possesses a higher ability to generate the open-chain-structure, resulting in stronger reducing properties. In this context the increasing reducing potential of the “non-reducing sugar” sucrose results from the acid hydrolyzed formation of invert sugar. Additional investigations at higher temperatures (90°C) and pH (5.2) provide evidence about the behavior of fermentable and unfermentable sugars during wort boiling. As a result the strong reducing potential of maltotriose in comparison to maltose is remarkable. In addition, the partial unexpected reduction potentials of sugars in the pH range of wort and beer have a direct influence on oxidative processes. In correlation to the measured reduction potential, the sugars show the same effect on oxidative processes during wort boiling as specific intermediate Maillard reaction products with reductone/endiol structure, resulting in an acceleration of radical generation (EPR spectroscopy) by the Fenton-/Haber-Weiss reaction mechanism and the formation of specific aging compounds (GC-MS oxygen indicator: 3-/2-methylbutanal). This phenomenon is demonstrably caused by the rapid reduction of Fe3+ to Fe2+ in direct dependence with the reduction properties, resulting in a higher activation of oxygen and stronger radical generation. In consideration of the reduction properties, the sugar profile of the wort should be characterized by a low content of fructose and maltotriose. In the case of non-fermentable sugars addition during wort boiling is disadvantageous. Our recommendation is direct addition before fermentation to avoid the negative effects on radical generation and to use the positive effect on SO2 formation during fermentation. Additional experiments provide information on the influences of the types of unfermentable sugar used on oxidative processes, aging compounds, and taste during storage.

After qualifying as a certified technician in preservation engineering (1991–1993), Thomas Kunz completed his basic studies in chemistry at the University of Applied Sciences, Isny (1994–1995), and his basic studies in food chemistry at Wuppertal University (1995–1998), before studying food technology at the University of Applied Sciences, Trier (1998–2002). After graduating, he worked as a chartered engineer in the area of ESR spectroscopy at the Institute of Bio Physics at Saarland University (2002–2004). Since January 2005, he has been employed as a Ph.D. student at the Research Institute of Brewing Sciences, Berlin Institute of Technology (Technische Universität Berlin). His main research focus lies in analyzing radical reaction mechanisms in beer and other beverages using ESR spectroscopy.