Real Extract & Real Attenuation Calculator
Real extract, apparent vs real degree of fermentation from original and final gravity.
How it works
A hydrometer in finished beer reads low because alcohol is less dense than water. Real extract uses the Balling regression to back out the alcohol and report the true residual sugar, then derives the matching attenuation figures. The headline is real extract in degrees Plato; apparent extract is simply the final gravity expressed in Plato for comparison.
RE = 0.1808 × OE + 0.8192 × AE (°Plato)
OE = original extract, AE = apparent extract (FG in Plato)
Sources: Balling real-extract regression, as documented by Brewer's Friend.
A regression estimate. It assumes normal wort and clean fermentation; sugar adjuncts and unusual worts shift the real/apparent relationship slightly.
Frequently asked questions
- What is the difference between real and apparent extract?
- Apparent extract is what a hydrometer reads in finished beer - it sits artificially low because alcohol is lighter than water and drags the reading down. Real extract corrects for that alcohol, so it reflects the true sugar left in the beer. Real extract is always higher than apparent extract.
- Why is real attenuation lower than apparent attenuation?
- Apparent attenuation is inflated by the same alcohol effect that depresses the hydrometer reading. Real attenuation removes that distortion and reports the actual fraction of extract the yeast consumed - typically about 80–82% of the apparent figure.
- What does real degree of fermentation tell me?
- It is the percentage of the original extract that was truly fermented, calculated from real (not apparent) extract. Brewers use it to compare attenuation across recipes without the alcohol artefact skewing the numbers.