How does this predict fermentation progress?

The calculator uses a sigmoid (S-curve) model that mimics real fermentation kinetics. After a lag phase where yeast acclimatise, fermentation accelerates through a log phase, then gradually slows as sugars are consumed. Temperature and yeast strain affect the curve shape.

Why does my actual gravity differ from the prediction?

Many factors affect real fermentation: yeast health, pitch rate, oxygen levels, nutrient availability, and wort composition. This model provides an estimate based on typical behaviour. Always verify with actual hydrometer readings.

The lag phase is the initial period after pitching where yeast are adapting to the wort environment. They absorb oxygen, synthesise sterols, and begin budding. Visible signs of fermentation (airlock activity, krausen) typically appear after the lag phase ends, usually 12-24 hours.

How does temperature affect fermentation speed?

Higher temperatures accelerate yeast metabolism and fermentation. Ales at 20C ferment roughly twice as fast as lagers at 10C. However, higher temperatures also increase ester and fusel alcohol production, so faster is not always better.

BrewCalcs

Fermentation Curve Tracker

Track and predict fermentation progress over time.

Original Gravity (OG)

Gravity reading before fermentation

Target Final Gravity (FG)

Gravity reading after fermentation

Yeast Strain

Fermentation Temperature

Temperature for this process

Days Since Pitch

Number of days

How We Calculate This

Sigmoid Fermentation Model

Progress = 1 / (1 + e^(-k x (t - t50))) where t is effective fermentation time adjusted for lag phase and temperature, k controls the steepness, and t50 is the half-completion time.

Expected Gravity

Current SG = OG - (OG - Expected FG) x Progress. The expected FG is derived from the yeast strain attenuation percentage.

Frequently Asked Questions

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Last updated: 2026-03-01

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