Beer color is a key quality factor as it is an important sensory attribute and defines the type of beer. If you are a commercial brewer, having a consistent color to your beer is not only key to your brand, but it could also indicate production problems.
Testing beer during the brewing process can help us quantitatively look at the fermentation. It allows for the detection of adulterants and false declarations and provides information for the label, such as the bitterness units and alcohol content. The American Society of Brewing Chemists, the European Brewing Convention and the Central European Commission of Brewing Analysis are a few of the large organizations that publish analytical methods for brewers to use.
In this article we will discuss UV-Visible spectroscopic methods that are used to confirm the quality of bottled beer as well as to evaluate quality during the brewing process.
Analysis via UV-Vis Spectroscopy
UV-Visible spectroscopy is a well-established analytical technique used in the food and beverage industry for testing in the quality control stage. The UV-Vis spectrophotometer was outfitted with software that provides the most important beer methods pre-programmed into the software, enabling simple sample analysis and results calculations.
UV-Visible spectroscopy measures the absorption or reflectance of light in the ultraviolet and /or visible region of the spectrum. In the most basic terms, spectrophotometers enable photometric comparisons of relative light intensities across the ultraviolet and visible spectrums. Directing a controlled, constant intensity light source (halogen, deuterium, or xenon) across the spectrum or at a specific wavelength through a sample easily can confirm known or calculate unknown characteristics of the sample. The incident light (I0) can be redirected backward as reflection, suffer an energy loss as absorption, and pass through transparent or translucent samples as transmission. (Read more about UV-Vis spectrophotometers.)
The Relationship Among Beer Ingredients, Processing, and Colors
There are four main ingredients in making beer: malt (partially germinated cereal grain), hops (the flowers, or cones, of a plant called Humulus lupulus), yeast (a unicellular fungi), and water (H2O). The color of beer is mainly due to the use of these different raw materials during the fermentation process and two important chemical reactions that make the grains in the fermentation process go from pale yellow to jet black: the Maillard reaction and caramelization. The Maillard reaction is a chemical reaction that occurs in the presence of heat between amino acids and reducing sugars in food, causing a change in color and flavor. Caramelization is a slow cooking process that occurs when sugar is cooked over low heat, causing a change in both appearance and flavor.
Color in many cases gives some indication of taste, thus customer preference. Lighter beer typically features light grainy flavors, whereas dark beers tend to showcase cocoa and coffee flavors. Color can also change as the beer ages and various components oxidize. Oxidation is a problem in beer production, often leading to off flavors because it is hard to control what the oxidation will do over time.
Therefore, it is critical in a production environment that color is consistent batch to batch. A color shift in a product can indicate what went wrong: a change in raw materials, too much heat at a step, or a pH change at a particular step in the fermentation process.
There are a couple of popular methods to measure color. The beer is first degassed, then the absorbance at 700 nm is measured to determine the absence of turbidity or anything that would scatter light. The simplest color measurement is performed at 430 nm which then places it on a beer color spectrum.
A second method to test beer color is the tristimulus color test which is a representation of color in a three-dimensional color space. This method is a better representation of the perceived color as it uses the absorbance across the visible range as opposed to only using the absorbance at a 430 nm. Many beers that have the same color as determined by the single wavelength method can differ significantly in appearance. By measuring the full visible spectrum, the color of these beers can be further differentiated from one another.
You can get more details about the analyses and results, including the beer color spectrum charts, equations, and the parameters and instruments used for the experiment by watching the webinar: UV-Vis Spectroscopy Techniques in Food and Beverage Analysis.
Whether your customers like your beer warm or cold, lager or ale, make sure that the color in the bottle is the color they expect.
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