Specific Gravity: A ratio of the density of a liquid compared to water. Water has a Specific Gravity of 1. In brewing, Specific Gravity measures the amount of sugars dissolved in the wort and the remaining sugars and alcohol after fermentation. Yeast consume the sugars and produce alcohol, which is lighter than water. Specific Gravity is therefore less after fermentation. The difference can be calculated into alcohol percentage and yeast attenuation.