Analytical Session
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.
ation 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.
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