Frank-Jürgen Methner (1), Leif-Alexander Garbe (2), Richard Glattfelder (1), Philip Wietstock (1); (1) Technische Universität Berlin, Berlin, Germany; (2) Hochschule Neubrandenburg, Germany
Packaging (Bottles, Draft, and Cans)
Absorption of a selection of hop volatiles representing different polarities and molecular sizes (myrcene, limonene, linalool, alpha-terpineol, geraniol, t-caryophyllene, alpha-humulene) by crown cork liner polymers and can coatings was investigated in model systems and in beer during storage. All volatiles measured were prone to migrate into the closures, and the absorption in a low-density polyethylene (LDPE) liner was demonstrated to fit well Fick’s 2nd law of diffusion for a plane sheet. The extent and rate of diffusion was significantly dissimilar and was greatly dependent on the nature of the volatile. Diffusion coefficients were deduced and were from highest to lowest in cm2/day: limonene, 1.32 × e–5; myrcene, 1.17 × e–5; linalool, 0.84 × e–5; alpha-terpineol, 0.72 × e–5; geraniol, 0.49 × e–5; t-caryophyllene, 0.32 × e–5; alpha-humulene, 0.26 × e–5. The maximum amounts found at equilibrium were in the order limonene > alpha-humulene > t-caryophyllene > myrcene >> linalool > alpha-terpineol > geraniol, although it is noteworthy that the terpene alcohols only diffused in the liner polymer at a maximum rate of 1.4%, while e.g., limonene was found at an amount of 105.7% as related to the initial amounts in the beer. Applying an LDPE liner with oxygen-scavenging functionality, an oxygen barrier liner made up of high-density polyethylene (HDPE), or a liner polymer from a different manufacturer had no significant effect on the composition of volatiles in beers after prolonged storage of 55 days at room temperature; however, significantly higher amounts of myrcene and limonene were found in the oxygen barrier-type crown cork, while all other closures tested contained similar amounts. Can coatings were demonstrated to absorb hop volatiles in a similar pattern as crown cork closures but to a lesser extent. The highest proportion of terpenes was still found in the can coating, but significantly higher percentages of myrcene were found in the beers. A short exposure time to the packaging material already yielded a high migration of certain compounds, which alters the original balance of the flavor compounds and, thus, results in flavor losses and flavor deterioration. This is the first time that the scalping of hop volatiles in beer systems was described by Fick’s second law of diffusion. Outcomes from this study point to the importance of scalping in beer systems and, therefore, will help improve closures and to “rethink” experimental designs when assessing hop aroma.
From 1975 to 1981 Frank-Jürgen Methner studied brewing science at the Technische Universität Berlin (TU Berlin). After graduating with a diploma-engineer, he worked as an operating supervisor at the Schlösser Brauerei in Düsseldorf, Germany. From 1982 to 1986, Frank did his degree dissertation at the TU Berlin, titled “Aroma Formation of Berliner Weissbier with Special Focus on Acids and Esters,” and worked on research projects. From 1987 to 2004, he was director at the Bitburger Brauerei, Bitburg, Germany, with responsibilities in R&D, as well as QA. Since 2004, Frank has held the chair of brewing science at TU Berlin.