Analyzing the Color of Beer with Spectrophotometry
With the naked eye, it is obvious that beer ranges in color from a translucent light yellow color and to a dark brown, almost black opaque color. The color of finished beer is determined by a multitude of different factors in the chemistry of its makeup and ingredients; which makes it difficult to predict in advance. For a long time, the final color was given a number that corresponded to something known as the Series 52 Lovibond Scale by matching it to a set of colored glass. There were a few problems with this method, one being that the hue of the glass was not always uniform from being manufactured at different factories. Also, relying on a visual evaluation proved to be somewhat accurate due to varying perceptions and instances of colorblindness. Due to these inconsistencies, this standard of measurement was eventually abandoned.
However, beer color is still routinely analyzed and assessed using a specific scale known as the Standard Reference Method. Major breweries have a more strict color requirement than craft brewers, but also have less instances of color changes since they continually manufacture the same beers.
In order to determine the SRM of a beer, a spectrophotometer is used to measure the depletion of light at 430 nm through a cm of beer. The beer is then assigned an SRM degree ranging from 2 to 40+ to grade its color intensity, with 2 as the lighter spectrum of beer and 40+ as the very darkest of beers. For home brewers without a spectrophotometer, a visual reference card was created to match to the beer. The card is printed on photographic paper and is pretty accurate for comparison of color to the SRM scale. The scale also correlates each color to common beers in order for people to understand where a certain type of beer should fall on the color scale. For example, a 2 would most likely fit the color of a pale lager and an example of its color would be a Michelob Ultra (with an actual rating of around 1.7.
Almost all large-scale breweries do rely on the spectrophotometer to determine the exact color of the beer they are producing. This ensures the beer adheres to a quality standard, as well as guaranteeing that different batches of the same beer are equal in color to each other.
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