Quantifying Beer Bitterness: An Investigation of the Impact of Sample Preparation

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-alpha-acid content in beer. In this exercise, students deviate from the standard UV-vis absorbance method and compare calculated bitterness (i.e., iso-alpha-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.