Degrees Brix (symbol °Bx) is a measurement of the dissolved sugar-to-water mass ratio of a liquid. It is measured with a saccharimeter that measures specific gravity of a liquid or more easily with a refractometer. A 25 °Bx solution is 25% (s/w), with 25 grams of sugar per 100 grams of solution. Or, to put it another way, there are 25 grams of sucrose sugar and 75 grams of water in the 100 grams of solution.
The Balling scale was developed by German chemist Karl Balling. It refers to the concentration of a dissolved solids (mostly sucrose) , as the weight percentage sucrose at 17.5 °C.
The Plato scale which measures in Plato degrees is also a refinement of the Balling scale. It uses a reference temperature of 17.5 °C and a slightly different modulus, with the approximation 260*(1 - 1/g), where g is the specific gravity of the solution at 17.5 °C.
Brix is used in the food industry for measuring the approximate amount of sugars in fruits, vegetables, juices, wine, soft drinks and in the starch and sugar manufacturing industry. Different countries use the scales in different industries; in the UK brewing is measured with specific gravity X 1000, European brewers use Plato degrees, and US industries use a mix of specific gravity, Brix, degrees Baumé and Plato degrees.
Since Brix is related to the concentration of dissolved solids (mostly sucrose) in a fluid it is therefore related to the specific gravity of the liquid. Because the specific gravity of sucrose solutions is well known, it can also be measured by refractometers.
Modern Brix meters are digital refractometers that calculate the Brix value based on refractive index. These meters are typically portable, splashproof and very simple to use, so that they can be operated easily with little training directly on location. More and more often Brix is measured to determine ideal harvesting times of fruit and vegetables so that products arrive at the consumers in a perfect state or are ideal for subsequent processing steps such as vinification.
When a refractometer is used, it is correct to report the result as "refractometric dried substance" (RDS). One might speak of a liquid as being 20 °Bx RDS. This is a measure of percent by weight of TOTAL dried solids and, although not technically the same as Brix degrees determined through a specific gravity method, renders an accurate measurement of sucrose content since the majority of dried solids are in fact sucrose. When an infrared Brix sensor is used, it measures the vibrational frequency of the sugar molecules, giving a Brix degrees measurement. This will not be the same measurement as Brix degrees using a density measurement because it will specifically measure dissolved sugar concentration instead of all dissolved solids. The index of refraction and density of mixtures such as ethanol and water are calculated using the Gladstone-Dale relation.
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