I couldn't resist this and it was really rather pleasant. So I thought finding out about specific gravity might be appropriate. It turns out specific gravity is actually the relative density ie the density of the brew divided by the density of water. That is more complicated than it sounds because water has different densities at different temperatures. Since it is a ratio, I'm not clear whether that is affected by the temperature or not. Specific gravity measurements are used to calculate the alcohol concentration of the beer. Since specific gravity is a ratio, it has no units.
