A Modified Procedure for Alcohol Determination by Dichromate Oxidation

Abstract

The chemical oxidation method for alcohol determination in wine after microdistillation of the samples is used routinely in many winery laboratories. However, analysts often experience a number of difficulties with the procedure, including use of the distilling apparatus and indicator endpoint when dichromate is titrated with ferrous ammonium sulfate. The procedure was modified to avoid some of the problems. Five ml of wine were distilled in a Cash volatile acid still, operated to ensure complete condensation and recovery of alcohol distillate in a 50-ml volume. Two ml of distillate were oxidized at 60°C with 10 ml of dichromate solution (34 g potassium dichromate plus 325 ml sulfuric acid per liter). Alcohol concentration was determined spectrophotometrically at 600 nm, according to Caputi et al. [Am. J. Enol. Vitic. 19:160-5 (1968)]. The method as modified provided acceptable speed, precision, and accuracy for routine analysis of wine alcohol.