Work out apparent attenuation instantly with clear inputs, formula shown and shareable results.
Apparent attenuation is the percentage drop in gravity points, but it overstates true fermentation because ethanol is less dense than water and depresses the hydrometer reading. Real attenuation is about 0.81 times apparent. Unfermentable dextrins set a floor below which gravity cannot fall.
Apparent attenuation
AA % = (OG points - FG points) x 100 / OG points
Real attenuation
RA % = apparent attenuation x 0.81
High mash temperature produces more unfermentable dextrins, and under-pitching, low oxygen, poor nutrient status or low fermentation temperature all cause the yeast to stall early.
Yes, with a very fermentable wort from a low-temperature mash or with added simple sugars. It can also signal a diastaticus or wild yeast contamination, which is a package safety risk.