Use of an Integrating Cavity Spectrometer to Easily Determine Beer SRM Color Without Filtration, Centrifugation or Numerical Correction

Abstract

Quantification of beer color of craft unfiltered, hazy, seltzer, and fruited beer styles can be problematic due to turbidity and unconventional ingredients. A novel integrating cavity spectrometer (ICS), designed to eliminate the effect of light scatter by the sample was employed to determine if it was able to more accurately quantify beer color compared to a conventional scanning spectrophotometer (CSS). A CSS was employed to measure the absorbance and transmission of 15 filtered and unfiltered craft brewery beer samples to determine the SRM color value and tristimulus color values. The ICS measures absorbance with a 430 nm LED to determine the single-point SRM value for each beer. The SRM values of unfiltered or 0.2 µm filtered beer samples were compared using Bland-Altman analysis and regression fits. Filtered and very clear beers showed strong agreement between the methods and Bland-Altman analysis confirmed their equivalence, particularly for SRM <25. Using the ICS alone, filtered beer versus unfiltered beer showed highly correlated values and narrow limits of agreement, successfully negating the effects of turbidity. In conclusion, SRM determination by ICS is equivalent to standard spectrophotometer single-point methods and superior in accurately determining the SRM color of hazy beers without filtration or centrifugation.

Keywords:

• SRM
• color
• CIE L*a*b*
• integrating cavity spectrometer
• turbidity

Acknowledgments

We wish to acknowledge Olis, Inc. for the CLARiTY 1 instrumentation and the UWEC Department of Chemistry and Biochemistry for support of this work. We are especially grateful to Eric Rykal of Modicum Brewing for his well-crafted beers and ongoing support and wisdom.