Color is often used as an indication of quality and freshness for food products; this especially applies to orange juice where a red-orange color is preferred. The HunterLab ColorFlex EZ instrument is widely used in the citrus industry to objectively measure the color of juices.
Originally citrus juice manufactures used subjective methods for evaluating sample color. They would perform visual comparisons of orange juice in a standard glass tube to a set of United States Department of Agriculture (USDA) plastic comparators also in glass tubes. The results of this method were often inconsistent and unreliable.
In the 1950s and 1960 several companies were performing research in the hopes of developing an instrument to objectively measure the color of orange juice. In the beginning HunterLab developed the D45 Citrus Meter. Although these meters can still be found in the industry today, HunterLab no longer manufactures this instrument. The current HunterLab instrument used for the measurement of orange juice is the ColorFlex EZ. This compact spectrophotometer is used to measure the color of fresh and concentrated orange, grapefruit, and lemon juice. Measurements are still taken with samples contained in the same kind of glass tube that was used for the early visual evaluations.
The ColorFlex EZ citrus reports Citrus Red (CR), Citrus Yellow (CY), and Citrus Number (CN.) These citrus values are all calculated from XYZ CIE Tristimulus Values. These quantitative values allow citrus producers to accurately evaluate the quality of their products.