Improvements of the Micro Method for More Rapid and Precise Determination of Vicinal Diketones in Beer

Abstract

The micro method proposed by Owades and Jakovac (18) for determination of vicinal diketones in beer was studied and improved as follows: 1) Temperature during gas sweeping of sample beer with CO₂ was raised to 90° C and the vicinal diketones were trapped after passing through a water-cooled condenser. 2) Percentage dimethylglyoxime formation under the conditions of the original method was found to be only about 85%. More than 60 min was required for complete conversion of vicinal diketones to their oximes. When hydroxylamine hydrochloride solution was used without neutralization, however, 10 min was sufficient for complete conversion. By heating the mixture of distillate and hydroxylamine hydrochloride solution after oxime formation for ca. 15 min in a boiling water bath with a small piece of bubbling stone, most of the ethanol in the mixture, which inhibits color development, was evaporated off. As a result, both the time required for the entire analysis and the variation coefficient were reduced to one half that of the original method. Total concentration of acetohydroxy acids and vicinal diketones could be determined by incubating the sample wort at pH 4.2 and 60°C for 30 min, followed by analysis according to the improved method.

• Acetohydroxy acid
• Beer
• Determination
• Diacetyl
• Vicinal diketone