The Oxford Companion to Beer definition of
Balling Scale is a measurement (expressed as °Balling) of the concentration of dissolved solids (mainly sugars) in a brewery wort. The concentration of dissolved sugars in the wort is an indicator of the potential alcoholic strength of the beer, as it is those sugars that the yeast will ferment into alcohol. The solids concentration can be measured most simply by using a hydrometer, an instrument used for measuring the specific gravity of a liquid (see hydrometer). Alternatively, the solids concentration of wort can be measured using a refractometer, an instrument for measuring the refractive index of a liquid.
The measurement scale was devised by the German chemist Karl Balling, who in 1843 established a set of tables relating the weight percentage of sucrose solutions to the specific gravity of the solution at a temperature of 17.5°C (63.5°F). The Balling scale has been largely superseded by the Brix and Plato scales, although all three scales are essentially the same. See plato gravity scale. The Balling and Brix scales are more commonly used in the wine industry to measure the sugar concentration in grape must and are rarely used in commercial brewing, whereas the Plato scale or specific gravity measurement is used to measure wort solids concentration. British brewers use the specific gravity figure multiplied by 1,000 to express wort “gravity”; a specific gravity of 1.048 becomes 1048 or 48 “degrees of gravity.” As an approximation, by dividing the degrees of gravity by four a figure for °Plato, °Balling, or °Brix can be derived, that is, 48 degrees of gravity approximates to 12 °Plato, Brix, or Balling. This, in turn, represents a sugar solution of approximately 12% by weight.