A. MUÑOZ INSA (1), M. Gastl (1), T. Becker (1); (1) Brewing and Beverage Technology, Freising, Germany

Quality
Wednesday, June 4 - 1:00 p.m.-2:45 p.m.
Level 3, Crystal Room

Lightstruck flavor is a widely known off-flavor in beer. It occurs in beer exposed to sunlight during storage. The main initiate substrate in this reaction is isohumulone, the isomerized form of the alpha-acid humulone from hops. The photodecomposition of isohumulone in the presence of riboflavin results in the formation of 3-methyl-2-buten-1-thiol (among other compounds). So far, other substances are known to initiate or inhibit lightstruck flavor formation. Whereas riboflavin, cysteine, and methionine are considered initiators, tryptophan and polyphenols work as off-flavor formation inhibitors. Tannin extract is a polyphenol-enriched hop product. It is obtained from the water-soluble fraction during the ethanol extraction process. The addition of tannin extract increases the polyphenol content in wort and beer. It contains mainly low molecular weight polyphenols with anti-oxidative properties (catechin, 2-MPPG, rutin, astragalin, and epigallocatechin gallate). Certain polyphenols are able to protect beer against light-induced oxidation by quenching the riboflavin triplet involved in the formation of 3-methyl-2-buten-1-thiol. Maximizing the content of polyphenols in beer gives a possibility to prevent lightstruck formation. The aim of this study was to specify suitable hop products to reduce lightstruck flavor perception in beer. Brewing trials were carried out with single hop product batches, and the finished beer was exposed to light. The beer with addition of tannin extract showed the lowest lightstruck flavor sensorial perception. Therefore it was selected for further trials. Time of addition and tannin extract dosage during boiling were adapted to maximize both the percentage of added polyphenols dissolving in wort and the total content of polyphenols in the finished beer. To validate the results and the impact of polyphenol content on lightstruck flavor formation, beers with 200, 100, 50, and 0% of the found tannin extract concentration were produced. To all beers an equal concentration of iso-extract was added during boiling to promote lightstruck flavor formation. After exposure to light, the tasting results conclude that the higher the tannin extract dosage the lower the lightstruck perception. Furthermore the effect of tannin extract addition on beer standard attributes was also evaluated. The amount of tannin extract had little to no influence on analytical beer attributes, but the sensorial profile was slightly altered.

Alicia Muñoz Insa was born in 1983 in Spain. She graduated with a Dipl.-Ing. degree from the Technical University of Madrid and carried out her diploma thesis at the Technical University of Munich. Since then she has been a Ph.D. student at the Chair of Brewing and Beverage Technology, TUM, working in the field of beverages from alternative cereals.