When diluting a hydroalcoholic mixture with water, the final volume is lower than the sum of the volume of water + the starting volume.
This article explains its origin. He presents a study which demonstrates that in the case where analysis by distillation requires dilution, it is nevertheless possible to obtain good precision in the measurement of the alcohol level.
The official method for determining the alcohol content of a spirit requires prior distillation to eliminate residues that could distort the density measurement. However, distillation does not completely eliminate all volatile compounds other than ethanol.
What about measurements made with automatic or semi-automatic devices, very selective for the analysis of ethanol, such as near infrared analyzers?
The analytical parameter “Obscuration” of a spirit corresponds to the difference between the real alcoholic strength by volume and the gross alcoholic strength by volume.
Where does this “Obscuration” come from?
To achieve the accuracy provided by the manufacturer, it is important to follow the rules for using an alcoholmeter.
To maintain this accuracy, it is equally important to follow certain maintenance instructions.