Brix

The °Bx is traditionally used in the wine, sugar, carbonated beverage, fruit juice, fresh produce, maple syrup, and honey industries.

In the early 1800s, Karl Balling, followed by Adolf Brix, and finally the Normal-Commissions under Fritz Plato, prepared pure sucrose solutions of known strength, measured their specific gravities and prepared tables of percent sucrose by mass vs. measured specific gravity.

Similarly, a vintner could enter the specific gravity of his must into the Brix table to obtain the °Bx, which is the concentration of sucrose by percent mass.

In modern times, hydrometers are still widely used, but where greater accuracy is required, an electronic oscillating U-tube meter may be employed.

Whichever means is used, the analyst enters the tables with specific gravity and takes out (using interpolation if necessary) the sugar content in percent by mass.

The ICUMSA tables are based on more recent measurements on sucrose, fructose, glucose and invert sugar, and they tabulate true density and weight in air at 20 °C against mass fraction.

Dissolution of sucrose and other sugars in water changes not only its specific gravity but its optical properties, in particular its refractive index and the extent to which it rotates the plane of linearly polarized light.

Formulas derived from the NBS table[4] above: Approximate (R2=0.999 98) values can be computed from: where SG is the apparent specific gravity of the solution at 20 °C/20 °C.

The Plato scale can be approximated with a mean average error of less than 0.02°P with the following equation:[7] or with even higher accuracy (average error less than 0.00053°P with respect to the ASBC tables) from the best-fit polynomial:[7] The difference between the °Bx and °P as calculated from the respective polynomials is: The difference is generally less than ±0.0005 °Bx or °P with the exception being for weak solutions.

Disagreements of this order of magnitude can be expected as the NBS and the ASBC used slightly different values for the density of air and pure water in their calculations for converting to apparent specific gravity.

Many refractometers have built in "Automatic Temperature Compensation" (ATC), which is based on knowledge of the way the refractive index of sucrose changes.

For example, the refractive index of a sucrose solution of strength less than 10 °Bx is such that a 1 °C change in temperature would cause the Brix reading to shift by about 0.06 °Bx.

It is important, therefore, that users of refractometers either make sure the sample and prism of the instrument are both close to 20 °C or, if that is difficult to ensure, readings should be taken at 2 temperatures separated by a few degrees, the change per degree noted and the final recorded value referenced to 20 °C using the Bx vs. Temp slope information.

In the first are the Abbe-based instruments in which a drop of the sample solution is placed on a prism; the result is observed through an eyepiece.

Due to higher accuracy and the ability to couple it with other measuring techniques (%CO2 and %alcohol), most soft drink companies and breweries use an oscillating U-tube density meter.

Where it is desirable to know the actual dry solids content, empirical correction formulas can be developed based on calibrations with solutions similar to those being tested.

As a consequence, a refractometer measurement made on a sugar solution once fermentation has begun results in a reading substantially higher than the actual solids content.

(If fermentation has indeed started, a correction can be made by estimating alcohol concentration from the original, pre-fermentation reading, termed "OG" by homebrewers.