Wine Fermentation Schedule Calculator

The Phases of Fermentation

Fermentation isn't a linear process. It follows a biological curve known as the yeast growth cycle:

1. Lag Phase (0-48 hours): Yeast acclimates to the environment, absorbing oxygen and nutrients. Little to no alcohol is produced yet.
2. Exponential Phase (2-5 days): The yeast population explodes. Sugar consumption is rapid, and the must generates significant heat and CO2. This is often called "tumultuous fermentation."
3. Stationary Phase (End of fermentation): Sugar levels deplete, alcohol rises, and yeast begins to die off or go dormant. The rate of bubbling slows down significantly.

Factors Influencing Speed

While sugar (Brix) and temperature are the main drivers, other factors play a huge role:

• Yeast Strain: Some strains, like EC-1118 (Prise de Mousse), are "powerhouses" that ferment quickly and cleanly. Others, especially wild yeasts or strains designed for complex aromatics, work much slower.
• Nutrients: Yeast needs nitrogen (YAN) to build cell walls. Adding nutrients like DAP (Diammonium Phosphate) or organic options like Fermaid O prevents "stuck" fermentations and speeds up the process.
• Temperature: For every 10°C increase, biological activity roughly doubles. However, fermenting too hot (over 30°C/86°F) can kill yeast and create "cooked" flavors.

Monitoring Progress (Brix Drop)

Winemakers track the "Brix drop" per day to ensure things are on track. A healthy red fermentation might drop 3-4 Brix per day during the peak. A slow, cool white fermentation might only drop 1-2 Brix per day.

Warning Signs: If the Brix stops dropping for more than 24 hours while sugar remains, you may have a "stuck fermentation." This can be caused by temperature shock or nutrient deficiency.

The Math Behind the Estimate

This calculator uses a baseline model adjusted for environmental factors. The core formula approximates the days required ($t$) based on deviation from standard conditions:

Where BaseDays is typically 7 for reds and 10 for whites. Nutrients reduce the time by roughly 10-15%.

Next Steps: Racking and Aging

Once the specific gravity reaches 1.000 or less (dry), active fermentation is complete. The next steps are:

• Racking: Siphon the wine off the sediment (lees) into a clean vessel (carboy or barrel).
• Secondary Fermentation (Optional): For many reds and some whites (like Chardonnay), Malolactic Fermentation (MLF) converts tart malic acid into softer lactic acid.
• Aging: The wine matures, integrating flavors and softening tannins.