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Brix & Refractive Index

What is Brix?

The Brix scale is a popular scale derived from the refractive index of a solution at 20 degrees Celsius (68 Fahrenheit). It was originally created by determining the percentage of sucrose (by weight) dissolved in a sucrose & water solution. In other words, dissolving 10g of sucrose in 90g of water would produce a 10% Brix solution. This simple scale has been used since the 19th century to quickly and accurately determine the concentration of a variety of liquids. Brix has also served as a foundation in the creation and use of many standardized scales used across different industries, including pharmaceuticals, cosmetics, automotive, and R & D.

One of the most common uses for Brix today is determining dissolved solids (sugar levels) in fresh produce. There is a direct correlation between a plant’s Brix value and its taste, nutritional density, and overall quality. Brix is also widely used in food and beverage processing. Changing the Brix even by a small amount can make a big difference between batches, so high-precision refractometers are used to maintain product consistency in the Quality Control lab.


The Brix scale has been adapted to other industries as well. Machining shops typically use Brix refractometers to determine the concentration of cutting oils and lubricants. Many fire departments also use Brix to check the concentration of fire-fighting foam. A farm, winery, condiment maker, fire department and machine shop could all use the same refractometer!

The Brix measurement of a liquid fluctuates according to temperature. The Brix of a cold sample will measure higher than the same sample at room-temperature. When measured hot, the Brix reading will be lower. To maintain consistent readings, we recommend to use a refractometer that features Automatic Temperature Compensation (ATC). ATC automatically adjusts the reading based on temperature, and displays the Brix as it would be at 20 Celsius. Without ATC, samples and measurements should be at room temperature (a temperature conversion table should be used in conjunction with non-ATC refractometers).

What is Refractive Index?

When light goes to medium x through air with a refractive index of air in the atmospheric pressure assumed as 1, the ratio of the of the sine of incident angle α against the interface to the sine of refractive angle ß is called the refractive index of the medium. Since the refractive index changes due to the temperature, and wavelength of light, it is expressed as follows:

For example, the refractive index of water at 20°C for the D line is expressed as n20/D= 1.33299 (generally it is expressed in the form of nD=1.33299).

Note: The refractive index measured by setting the refractive index of vacuum to 1 is called the absolute refractive index, but it is generally scarcely used.

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