Crest silver award: Measuring alcohol content

The aim of this project is to investigate the properties of alcohol/water mixtures, and how these properties can be used to measure alcohol content. The alcohol in drinks is ethanol, C₂H₅OH. However, the ethanol used in the laboratory has been methylated by adding 5% of methanol, CH₃OH. This avoids having to pay duty, because methanol is toxic, so methylated ethanol is not drinkable.  Students complete 30 hours of independent project work, starting by finding out about historical methods of measuring alcohol content.

They then investigate how to measure the specific gravity of a brew using a hydrometer, the difference between specific gravity and density, why these change during fermentation, and how density varies with alcohol content.

Students should then set up a fermentation brew and measure its density as accurately and precisely as possible at intervals, carefully prepare ethanol/water mixtures up to 50% alcohol by volume (ABV), and measure their densities, suggesting reasons for the differences in readings.