Included is a letter as well as some graphs that I believe will make up a body of evidence sufficient to clear up the question of non-linearity in the measurement of beer color using absorbance measurements. I hope you will print it as it reveals some important misconceptions with the technique of spectrophotometry. However, the application of Beer's Law to the determinations of beer color is yet to be clarified. Beer does conform to Beer's Law and Mr. Ed Hitchcock is correct in his assertion that the non-linearity observed in absorbance curves of dark beer dilutions is due to measurement error caused by limitations in the technique of spectrophotometry.
Spectrophotometers measure the intensity of a beam of light that exists in a sample.
In practice this is not observed due to limitations in the spectrophotometer itself. These devices split intense white light into the spectrum of wavelengths using a prism or diffraction grating. Mechanical imperfections cause individual wavelengths to become contaminated with light of other wavelengths. This contaminating light is called stray light and may include wavelengths that do not interact with the sample. The error is magnified by the log transformation causing depression in the observed absorbance values when compared to the expected absorbance values.