[Ansire2333]

How to measure the amount of ethanol in a aqeous solution?

[Ansire2333]

The solution contains sugar and yeast. Basically a fermenting liquid.

[Borek]

There is no simple, cheap method.

Common approach is to measure the density - while it doesn't tell exactly what is the composition, it allows comparing with other batches and keeping track of changes during fermentation. If memory serves me well for many typical cases there are tables that tell how the density changes and what is the ethanol concentration (they are not universal, as amount of sugar is the second unknown).

[Corribus]

This may be helpful.

https://www.nist.gov/how-do-you-measure-it/how-do-you-measure-percentage-alcohol-beer-wine-and-other-beverages

You can basically measure density or measure sugar (since loss of sugar = gain in ethanol).