If you were yeast, attenuation would simply be how much of your restaurant meal you actually consumed:
- 100 percent attenuation means you cleaned your plate.
- 75 percent attenuation means you took home about a quarter of your dinner in a doggy bag.
- 50 percent attenuation means you probably should have split an entrée with your dining partner.
- 0 percent attenuation means you lost your appetite after ordering.
A highly attenuative yeast strain consumes more wort sugars than a strain that exhibits lesser attenuation. While each yeast is unique, Belgian strains tend to attenuate a lot, American strains moderately, and English strains less enthusiastically.
But we have to be careful: Attenuation is how much sugar the yeast eats, but this isn’t what we measure. Brewers use the hydrometer to measure a beer’s original and final gravities, which, in turn, indicate the density of a solution. Wort density increases with the amount of sugar dissolved in it, so density is an accurate proxy for the _real extract _of a sugar solution.