From carbonated soft drinks, fruit/vegetable juices, and milk to coffee, tea, hot chocolate, as well as spirits – beverages can be opaque, translucent or transparent, and will require different instrumentation and techniques for successful color measurement.
Opaque Liquids usually have a high solids content, are impenetrable by light, and are usually characterized by a high Brix value. These type samples are best measured using Directional 45/0° reflectance instrumentation. This is the geometry that most closely matches how the human eye sees color.
Translucent Liquids possess a medium level of solids content, along with a lower Brix value and allow light to pass through, but only diffusely, so that objects on the other side cannot be clearly distinguished. Both reflective and transmittance measurement modes may work well depending on the translucency of the sample. As a rule of thumb,
- If at the path length that your customer will view the sample, you can see slight details of your thumb or finger through the liquid, the transmittance is the preferred measurement method.
- If you cannot see slight details, then reflectance measurement using directional 45°/0° is preferred, though it is also possible to use diffuse d/8° sphere geometry.
Path length is defined as the thickness of the sample from where the light enters to where it exits the sample. A simple test to determine the translucency is to pour the liquid into a clear container that simulates the thickness that the sample will normally be viewed, and hold your thumb on the back of the container and look through the sample.
Transparent Liquids have a very low, or zero, solids content and allow light to pass through with little or no interruption or distortion so that objects on the other side can be clearly seen. These liquids can only be measured using transmission instrumentation.