Fermentation
Apparent and real attenuation
1.050 then 1.010 is 80% apparent attenuation. Your yeast promised 75 to 80%: all is well.
Result
Fill in the values and run the calculation, or try the example.
This is the calculation Krausi uses. Create an account to save it in a recipe or a brew.
Create my accountWhy calculate attenuation?
Attenuation is the share of the wort sugars that the yeast has converted. Each strain has its own, stated by the manufacturer: 70 to 75% for an English yeast, 78 to 85% for a saison yeast.
Comparing the measured attenuation with the stated one answers the question every brewer asks: is fermentation finished? If you are within the range and the gravity no longer moves, you can bottle. If you are ten points below, the yeast is not done, and bottling would be dangerous.
How is attenuation calculated?
Apparent attenuation is calculated directly from the gravities:
apparent attenuation (%) = (OG − FG) / (OG − 1) × 100It is called apparent because alcohol, being less dense than water, skews the hydrometer reading: the beer looks more attenuated than it is. Real attenuation corrects this effect with Balling's formula, in degrees Plato:
real extract = 0.1808 × original extract + 0.8192 × apparent extract
real attenuation (%) = (original extract − real extract) / original extract × 100Yeast manufacturers state the apparent attenuation: that is the one to compare.
Worked example
Values entered
- Original gravity as decimal SG: 1.05
- Final gravity as decimal SG: 1.01
Result from the tool
- Apparent attenuation in %
- 80 %
- Real attenuation in %
- 64.96 %
- Original extract (OE) in °P
- 12.39
- Real extract (RE) in °P
- 4.34
What the tool does not do
- A normal attenuation does not prove that fermentation is finished: compare two readings 48 hours apart.
- Gravities must be read at 20 °C, on a degassed sample.
- Attenuation depends on the mash temperature as much as on the yeast.
Frequently asked questions
What attenuation is normal?
Between 70 and 85% apparent attenuation for most yeasts. Below 65%, look for a cause: temperature too low, too little yeast, or a mash step that was too hot.
Apparent or real attenuation, which one should I look at?
The apparent one: it is the one manufacturers and all brewing software state. The real one is mostly used to calculate calories and to compare very different beers.
And with the assistant?
Send every gravity reading to Krausi by e-mail: he updates the curve and calculates the attenuation each time.
Gravity 1.010 this morning, I started from 1.050.
Reading logged. You are at 80% apparent attenuation, at the top of your yeast's range. If the gravity is the same the day after tomorrow, fermentation is finished.