Attenuation measures how much of the fermentable sugars were consumed by yeast. This calculator determines both apparent and real attenuation, plus real extract and calorie content.

Starting gravity of wort (e.g., 1.055)
Gravity after fermentation complete (e.g., 1.012)

📚 Understanding Attenuation

Attenuation is the percentage of sugars converted to alcohol and CO₂ during fermentation. Higher attenuation means more sugar was consumed, resulting in a drier beer with lower residual sweetness.

Apparent vs Real Attenuation

Apparent Attenuation (AA)

Calculated from gravity readings using a hydrometer. Appears higher than actual because alcohol is less dense than water, making the beer seem more attenuated than it really is.

Formula: AA = ((OG - FG) / (OG - 1)) × 100

Real Attenuation (RA)

The actual percentage of extract consumed by yeast. Corrects for alcohol's lower density to show true sugar consumption.

Formula: RA = ((OE - RE) / OE) × 100

Typical Attenuation Ranges

Low (65-70%)
Full-bodied, sweet beers - English ales, Scottish ales, some Belgian styles
Medium (70-77%)
Most ales - American ales, IPAs, amber ales, standard fermentation
High (77-85%)
Dry, crisp beers - Saisons, Belgian strong ales, brut IPAs, champagne yeast
Very High (85%+)
Extremely dry - Brut IPA with enzymes, some wild fermentations

Factors Affecting Attenuation

  • Yeast strain: Each strain has characteristic attenuation (e.g., WLP001 75-80%)
  • Mash temperature: Lower temps (148-150°F) = higher attenuation
  • Grain bill: More simple sugars = higher attenuation
  • Fermentation temperature: Must be in yeast's optimal range
  • Yeast health: Fresh, properly pitched yeast attenuates better
  • Wort aeration: Proper oxygen helps yeast work efficiently

Troubleshooting Low Attenuation

  • Stuck fermentation? Check if gravity stable for 3+ days
  • Temperature too low? Raise temp gradually to yeast's upper range
  • Under-pitched? Add more yeast or make a starter
  • Old yeast? Check manufacture date and viability
  • Insufficient aeration? Yeast needs oxygen at start
  • High mash temp? Creates more unfermentable sugars

Increasing Attenuation

  • Lower mash temperature (148-150°F for highly fermentable wort)
  • Use highly attenuative yeast (US-05, WLP001, Saison strains)
  • Ensure proper pitch rate and yeast health
  • Ferment at optimal temperature for strain
  • Add simple sugars (dextrose) - 100% fermentable
  • Use enzymes (amylase) to break down complex sugars

Frequently Asked Questions

What is the difference between apparent and real attenuation?

Apparent attenuation is calculated from hydrometer readings and appears higher because alcohol is less dense than water. Real attenuation corrects for alcohol's lower density to show the true percentage of sugars consumed by yeast. For example, 75% apparent attenuation typically equals about 61% real attenuation.

What is a good attenuation percentage for beer?

Most ales target 70-77% apparent attenuation, while lagers often achieve 75-82%. Lower attenuation (65-70%) produces fuller-bodied, sweeter beers like English ales. Higher attenuation (77-85%) creates drier, crisper beers like saisons and brut IPAs. The ideal range depends on your beer style.

Why is my beer not attenuating properly?

Common causes of low attenuation include insufficient yeast pitch rate, low fermentation temperature, old or unhealthy yeast, inadequate wort aeration, high mash temperature (creating unfermentable sugars), or using specialty malts that limit fermentability. Check that your gravity has been stable for 3+ days before troubleshooting.

How can I increase attenuation in my beer?

To increase attenuation: lower your mash temperature to 148-150°F, use highly attenuative yeast strains (like US-05 or saison yeasts), ensure proper yeast pitch rate and health, ferment at optimal temperatures, add simple sugars like dextrose, or use amylase enzymes to break down complex sugars. Proper oxygenation at pitching also helps.

Does higher attenuation mean higher alcohol content?

Yes, higher attenuation typically means higher alcohol content for the same original gravity, because more sugars have been converted to alcohol. However, it also means less residual sweetness and a drier finish. The relationship between attenuation and ABV depends on your starting gravity.

Can I use this calculator for wine or mead?

While this calculator uses beer-specific formulas, the concept of attenuation applies to all fermented beverages. Wine and mead typically achieve higher attenuation (often 85-100%) because they contain more simple sugars. The ABV and calorie calculations will still be accurate for any fermented beverage.