Barnes, P. S., HunterLab, Reston, VA, USA
Poster
Sensory evaluation is very important in the evaluation of beer. Specifically, color and visual appearance are critical factors in consumer acceptance, while also being an indication of overall quality and process variation. The ASBC method for beer color and turbidity is: ASBC Beer-10, Color of Beer Part A, Spectrophotometric Color Method. The ASBC color metric is based on a spectral absorbance measurement at 430 nm of clarified beer using a UV-VIS spectrophotometer. The ASBC Beer Color scale has a range of approximately 1 to 11 units. The higher the ASBC Beer Color value, the lighter the beer. ASBC turbidity is also based on a spectral method that measures absorbance at two points—one in the blue (430 nm) and one in the red (700 nm) region. If the absorbance is significantly different at these two points, then ASBC turbidity is rated as being “turbid,” if not then the rating is “free of turbidity.” The key industry challenges of appearance measurement for beer are that: the current color measurement method does not reproduce how the eye sees color; a beer color number can be the same for products that are visually different (data and examples discussed); turbidity is generally not quantified, only qualitatively evaluated (data and examples discussed); and visual consistency from lot-to-lot of the same beer type would also be important. An additional global analytical method can be utilized for precise color and turbidity evaluation. This additional analytical method uses well-established colorimetry and color science. Both ASBC color and turbidity metrics use objective quantification as a basis. Both are more consistent than visual evaluation of color and scattering in beer samples. However, for ASBC color, only a single wavelength is used for quantification. The CIE colorimetric scales, defined in the paper, offer a complete quantification of product color. The situation regarding ASBC turbidity is similar. While based on spectral measurement and useful for reporting for product specification, the reported values are based on only two wavelengths. For this situation, either ASTM D1003 transmission haze or NTU turbidity measurement can be utilized. Both report product scattering in a quantifiable scale based on spectrophotometric measurement. The specifications and methods will be discussed. In addition, the talk will describe how color science is used to evaluate and communicate color and provide a more accurate color measurement, including color scales and basic color measurement techniques. Turbidity evaluation and quantification for beer will also be discussed.
Paul Barnes has over 30 years of experience in analytical instrumentation methods. He has spoken to numerous food and beverage industry groups on color science and applications. He holds a B.S. in chemistry from the University of Maryland, College Park, and M.S. degree from Johns Hopkins University.
View Presentation
