Greg Rahn, Hamilton College
Co-author(s): Tim Elgren, Hamilton College, USA; Mike Adler, The Matt Brewing Company, USA
ABSTRACT: Vicinal diketones (specifically 2,3-butanedione [diacetyl] and 2,3-pentanedione) are chemical compounds mainly produced during fermentation of wort. They are produced as a by-product of valine synthesis, when alpha-acetolactate and alpha-acetohydroxybutyrate are decarboxylated and are later enzymatically reduced to acetoin and 3-hydroxy-2-pentanone. However, diacetyl can also arise due to bacterial contamination without the development of 2,3-pentanedione. Having quantification of both compounds completed quickly and easily is much more useful than the standard 7 days that a complete microbiological examination would take. They can play a role in beer maturation indices as they are among the last processes that occur during fermentation. Current decisions as to adequate beer aging and storage are typically time-based. If evaluation of these maturation markers occurred in real time, adjustments in temperature or holding time in a fermentation vessel could be made to both enhance the quality of the finished product and to reduce the time that the beer needs to mature. The end result of both is a superior product and better tank utilization, which makes this an invaluable tool in adjusting fermentation profiles. In order to assess potential bacterial contamination of newly fermented wort and monitor these same chemical markers as proxies for beer maturation, accurate and precise updated methodology was sought. Existing methods (EBC Method 9.24.2) based on gas chromatography and electron capture detection had labor-intensive sample preparation steps and potential interferences from endogenous compounds. It also suffered in that an experienced scientist was needed to carry out the procedures. Our goal was to simplify the method, especially the sample preparation portion, make it less technical so someone less skilled (undergraduate students) could perform it, yet ensure the integrity of the results through direct comparison of samples analyzed using both methods. This updated method uses automated static headspace electron capture detection (ECD) with “dilute-and-shoot” sample preparation and monitors low ppb levels of both vicinal diketones using 2,3-hexanedione as an internal standard. The use of this internal standard ensures quantitative accuracy since it compensates for any and all unanticipated method shortfalls. When the virtues of this new method were realized through direct sample read-back comparisons, a 3-day validation of it was performed. This validation comprised the statistical evaluation of sample results from student prepared standards, quality control samples, and spiked and real samples. In addition, stability assessments of stored, in-process, and prepared samples were made to further ensure the accuracy of sample result reporting. This poster will detail the updated methodology, discuss the accuracy and precision of it through an in-depth evaluation of the sample results generated during the course of the validation, and demonstrate how analysis of real process samples leads to informed decisions regarding beer maturity.
Greg Rahn is currently an instrumentation specialist in the Department of Chemistry at Hamilton College in Clinton, NY. He received a B.S. degree in chemistry in 1981 at the State University of NY College at Cortland. He joined the Hamilton staff in 2008 after more than 25 years of developing and implementing analytical services in the environmental and pharmaceutical industries. With general expertise in analytical methodologies, his primary expertise is in the area of mass spectrometry.