When choosing a beverage product from the store shelf, consumers not only demand superb taste, but also consistency in the way the beverage looks to the human eye. Color and transparency are essential markers for quality - any imperfection can indicate contamination, impurities in the raw materials, or process variations caused by heating and oxidation.
However, drinks like fruit and vegetable juice, beer, and blended cocktails are difficult for manufacturers to control during production. Natural ingredients like fruit can vary in color. Raw ingredients for beverage blends can include any combination of liquids, solids, and powders, and even a small change in lot-to-lot color can make a big difference in the color of the final mix.
To control the color of liquids for consistent color appearance, you need the right tools to collect color data and the right processes in place to identify and correct color variations.
Tools for Color Measurement of Liquids
1 - A Spectrophotometer
To measure liquids, visual tests are not enough. You need an optimum precision spectrophotometer that takes non-contact measurements to avoid contaminating the color sample and coating the optics, which would skew the measurement and potentially damage the spectrophotometer. Next, you need to determine whether you need a reflectance or transmission spectrophotometer based on the opacity or translucency of the liquid.
To Measure Opaque Liquids
To measure the color of opaque liquids like apple cider, dark beer, and orange juice, you can use a reflectance spectrophotometer. A glass test tube holder is mounted on the front of the device to hold the opaque liquid in the right location for color measurement. The measurement device shines light onto the sample and captures the illumination that reflects back into the optics to quantify the color data.
To Measure Translucent Liquids
A reflectance measurement will not work for clear dyes and beverages like apple juice, white wine, mineral oil, vinegar, olive oil, and light beer, which have color but are usually translucent. The wavelengths of light will go right through the sample instead of bouncing back. To measure translucent liquids, you need a spectrophotometer that can measure in transmission mode.
Transmission spectrophotometers allow you to put a liquid sample inside the instrument in glass test tubes or cuvettes. The device shines visible spectrum illumination through the sample and receivers on the other side capture the percentage of light that passes through at numerous wavelengths. A relatively transparent liquid will absorb some components of white light, while allowing other components to pass through. This data is used to quantify the color of the sample.
To Measure Both Opaque and Translucent Liquids
If you measure both, you don't necessarily need two devices. Many benchtop spectrophotometers are capable of measuring in both reflectance and transmission modes.
Not sure which type of device is best for your liquid color measurement needs? Check out our Transmission vs. Reflection: Which Benchtop is Right? blog.
2 - Quality Control Software
Regardless of whether you're measuring the color of transparent liquids using transmittance measurements or opaque liquids using reflectance measurements, quality control software can help you quantify the resulting values. To do this, you can enter a known standard or CIE colorimetric standard and compare it against the measured sample to see if it passes or fails the set tolerance. The software will plot the standard and sample in a L*a*b* plot in color space as a visual representation of results.
Here's what you can learn from color measurement data.
Is the color accurate?
Color measurement data from QC software can tell you if the color you produced is in tolerance. If the liquid is a blend, you might be able to adjust the type and amount of colorants to change the color, and software can help you quantify what you need to add to bring it into tolerance.
Is the liquid too opaque or transparent?
Color measurement data can tell you not enough light is passing through, indicating you need to filter out pulp or impurities. On the other hand, if the liquid is too transparent, it can help you determine how much to increase the dye.
Does it meet a color scale index or earn a quality grade?
For natural beverages or liquids like gasoline, you can't add additional dyes to change the color. In these cases, color measurement data can tell you if your product meets ASTM defined international standards and color scales for grading. For example, there is a color scale calculation called the OJ index. While a lighter batch of oranges may still produce a delicious juice blend, a pale color can jeopardize USDA approval and leave the consumer questioning the quality. To sell orange juice, you can use the single number from QC software to prove compliance with ASTM standards and justify selling your product for a higher cost.
