Fermentation Tracker

Plan your fermentation timeline, log gravity readings, and troubleshoot issues. Track ales, lagers, and specialty styles with temperature guidance.

Gravity Readings

How to Use the Fermentation Tracker

  1. Set your beer style: Choose ale or lager to get the appropriate fermentation temperature range and timeline recommendations for your brew.
  2. Log gravity readings: Enter your original gravity (OG) and subsequent specific gravity readings over time. The tool calculates apparent attenuation and estimated alcohol by volume (ABV).
  3. Track the timeline: The tracker shows expected fermentation phases — active fermentation, diacetyl rest (for lagers), conditioning, and packaging — with recommended temperatures for each phase.
  4. Monitor completion: The tool helps you determine when fermentation is complete by tracking stable gravity readings over consecutive days.

Understanding Beer Fermentation

Fermentation is the metabolic process by which yeast converts sugars in wort into alcohol and carbon dioxide. After brewing and cooling the wort, yeast is pitched (added) and begins consuming the fermentable sugars produced during mashing. Ale yeasts (Saccharomyces cerevisiae) ferment at warmer temperatures (18 to 24 degrees Celsius) and typically complete in 1 to 2 weeks. Lager yeasts (Saccharomyces pastorianus) ferment cooler (7 to 13 degrees Celsius) and require extended cold conditioning (lagering) for several weeks to develop their characteristic clean profile.

Gravity readings measure the density of your beer relative to water and indicate how much sugar remains unfermented. Original gravity (OG) is measured before fermentation begins, and final gravity (FG) is measured when fermentation is complete. The difference between OG and FG reveals how much sugar was consumed, allowing you to calculate ABV using the formula: ABV approximately equals (OG - FG) multiplied by 131.25. Stable gravity readings over two to three days indicate that fermentation is complete.

Temperature control is the single most important factor in producing quality beer. Fermenting too warm can produce excessive esters and fusel alcohols, creating fruity or solvent-like off-flavors. Fermenting too cold can stall fermentation or cause yeast to go dormant. A diacetyl rest — raising the temperature near the end of fermentation — allows yeast to reabsorb diacetyl, a buttery off-flavor common in lagers. Stuck fermentation, where yeast stops working before consuming all sugars, can be caused by old yeast, insufficient nutrients, or temperature shock, and may require repitching or gentle warming to restart.

Frequently Asked Questions

How long does beer fermentation take?
Ales typically ferment in 7-14 days at 18-22°C. Lagers take 2-4 weeks at 10-14°C, followed by 2-6 weeks of lagering at 0-2°C. High-gravity beers (OG > 1.070) may take 3+ weeks. Kveik strains can finish in 3-5 days at 30-40°C.
What is a diacetyl rest?
A diacetyl rest involves raising the fermentation temperature near the end of primary fermentation (typically for lagers) to 16-18°C for 2-3 days. This allows yeast to reabsorb diacetyl (a buttery off-flavor). It is done when gravity is 2-5 points above expected FG.
What causes stuck fermentation?
Common causes: under-pitching yeast, old/dead yeast, temperature too low, poor wort aeration, high alcohol toxicity (>12%), lack of yeast nutrients, or abrupt temperature drops. Fix by raising temperature, adding yeast nutrient, or pitching active yeast starter.
How do I know fermentation is done?
Take gravity readings 2-3 days apart. If the reading does not change by more than 0.001 SG, fermentation is likely complete. The beer should also be at or near your expected final gravity. For lagers, ensure the diacetyl rest is completed before cold crashing.
Why is temperature control important?
Temperature directly affects yeast behavior. Too warm: excessive esters (fruity), fusel alcohols (hot/solvent), and stress. Too cold: sluggish fermentation, incomplete attenuation, and diacetyl. Different styles need different temperature ranges for optimal flavor profiles.
What is lagering?
Lagering is cold storage (0-2°C / 32-36°F) of fermented lager beer for 2-6 weeks. This allows yeast and proteins to settle, rounds off flavors, and produces the clean, crisp character associated with lagers.
How do I know when fermentation is complete?
Fermentation is complete when you get the same specific gravity reading on three consecutive days. Visual signs include the airlock slowing to a stop, the krausen (foam cap) falling, and the beer clearing. Always confirm with a hydrometer rather than relying on visual cues alone.
What is a diacetyl rest?
A diacetyl rest is a technique used primarily for lagers where the fermentation temperature is raised to around 18 degrees Celsius for 2 to 3 days near the end of fermentation. This allows the yeast to reabsorb diacetyl, a compound that produces an undesirable buttery flavor, resulting in a cleaner-tasting beer.
What causes stuck fermentation?
Stuck fermentation can be caused by several factors: old or under-pitched yeast, insufficient wort nutrients, temperature shock (rapid cooling), or excessively high original gravity. Solutions include warming the fermenter slightly, rousing the yeast by gently swirling, adding yeast nutrient, or repitching with fresh, healthy yeast.

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