Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX
pubs.acs.org/jchemeduc
Quantifying Beer Bitterness: An Investigation of the Impact of Sample Preparation Rebecca A. Hunter* and Eric J. Dompkowski Department of Chemistry, The Citadel, 171 Moultrie Street, Charleston, South Carolina 29409, United States
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S Supporting Information *
ABSTRACT: Much of analytical chemistry involves the analysis of complex mixtures, where careful attention to sample preparation and method selectivity is required to avoid interferents and obtain accurate data. As this type of analysis is very different from simple colorimetric analysis that most students are exposed to in general chemistry, this laboratory exercise was developed to help students discover the importance of sample preparation, specifically extraction and pH adjustment, for quantifying the “bitterness” derived from iso-α-acid content in beer. In this exercise, students deviate from the standard UV−vis absorbance method and compare calculated bitterness (i.e., iso-α-acid concentration) to the beer manufacturer’s reported bitterness, helping them clarify how the standard method works and why the beer must be “cleaned up” prior to analysis. KEYWORDS: Second-Year Undergraduate, Analytical Chemistry, Laboratory Instruction, Hands-On Learning/Manipulatives, Quantitative Analysis, Equilibrium, UV−Vis Spectroscopy acid content has a significant impact on the flavor profile of beer, the estimated concentration of iso-α-acids is relevant to both brewers and consumers and is typically reported as a unitless figure known as International Bitterness Units (IBU), where 1 IBU is equivalent to ∼1 mg L−1 iso-α-acid. The standard method for determining the IBU of beer requires the extraction of iso-α-acids and other bittering substances from acidified beer using iso-octane.15 This extraction is very efficient, with an expected partition coefficient of >10 when the aqueous phase has a pH
