What is apparent attenuation?

Apparent attenuation is the percentage of sugars consumed by yeast during fermentation, as measured by a hydrometer. Most ale yeasts attenuate between 70-80%, while some Belgian strains and saison yeasts can exceed 85%.

What affects final gravity?

Mash temperature (higher = less fermentable wort), yeast strain and health, fermentation temperature, grain bill composition (more crystal/caramel malts = higher FG), and adjuncts like lactose which are unfermentable.

How do I know fermentation is complete?

Take gravity readings on consecutive days. When the reading is stable for 2-3 days, fermentation is likely complete. Most ales finish within 7-14 days, lagers may take 3-6 weeks.

What if my FG is too high?

A higher-than-expected FG can indicate stuck fermentation. Try raising temperature slightly, rousing the yeast, or adding a more attenuative yeast. Check that you had healthy yeast and proper pitch rate.

Where do I find my yeast attenuation percentage?

Check the yeast manufacturer website or packet. Wyeast, White Labs, and Fermentis all publish attenuation ranges for each strain. Most ale yeasts fall between 70-80% apparent attenuation. Use the midpoint of the range as a starting estimate.

BrewCalcs

Final Gravity Calculator — Estimate FG

Estimate your expected final gravity based on original gravity and yeast attenuation.

Original Gravity (OG)

Yeast Attenuation

Check your yeast packet for typical range

How We Calculate This

The FG Formula

Final gravity is estimated using: FG = 1 + ((OG - 1) x (1 - attenuation/100)). This takes the original gravity points and reduces them by the yeast attenuation percentage to estimate where fermentation will finish.

Yeast Attenuation Ranges

Different yeast strains have different attenuation ranges: English Ale 70-75%, American Ale 73-77%, Belgian Ale 74-82%, Saison 85-95%, Lager 73-77%. The actual attenuation depends on wort fermentability and fermentation conditions.

Frequently Asked Questions

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Attenuation Calculator

Calculate apparent and real attenuation of your fermentation.

Last updated: 2025-02-20

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.