🍷 Brix

Degree Brix (°Bx) expresses the soluble solids content of grape juice as a percentage by mass of sucrose (saccharose). The OIV method for soluble solids in grape juice (resolution OIV-OENO 662F-2023, based on Compendium method OIV-MA-AS2-02) estimates them from the refractive index of the sample at 20 °C and covers concentrations from 10.0 to 69.2 °Bx.

The Abbe refractometer must measure at 20 °C plus or minus 5 °C and have a scale showing either percentage by mass of sucrose to 0.1 % or refractive index to four decimal places; an electronic refractometer is also acceptable and needs no temperature correction if it compensates automatically. Readings taken away from 20 °C are corrected with a temperature table, and a second OIV table converts the result to grams per litre and grams per kilogram. The sample is filtered, and at least two determinations are made on the same prepared sample.

The earlier text of method OIV-MA-AS2-02 (Oeno 21/2004, revised by Oeno 466/2012) deals with grape musts, concentrated musts and rectified concentrated musts in the same way. Rectified concentrated must is made up from 200 g to 500 g with water before reading, and the sugar concentration is expressed as invert sugar to one decimal place.

According to Oregon State University Extension (Osborne, 2023), winemakers use Brix to estimate the potential ethanol of the finished wine, but it is not equal to fermentable sugars: glucose and fructose are often higher than the Brix value. For a more accurate estimate the publication gives potential ethanol (% v/v) as the sum of glucose and fructose in g/L divided by 16.83. Yeast strain and fermentation temperature also affect the final ethanol.