Hydrometer doesn't check the alcohol content. It measures the density of the liquid, but the density is function of the concentration of everything that is dissolved - alcohol, sugars, salts and so on. No way to determine alcohol content from a single density measurement. At best, assuming everything else is kept constant you could do some comparison - this sample contains more, this sample contains less. But there is no way to keep everything else constant while cooking different foods.
Chromatography is IMHO the only viable option.