A stalled fermentation is one of the most stressful challenges a winemaker can face. However, before taking drastic measures that could impact the delicate flavor profile of your vintage, it is vital to approach the situation with technical precision.
Follow this diagnostic protocol to identify if your wine is truly stuck and how to safely guide it to dryness.
1. Verify with a Hydrometer (Mandatory)
The most common cause of a "false" stuck fermentation is relying on an inappropriate measurement tool. You must use a glass hydrometer to confirm your Specific Gravity (SG) or Brix. Do not use a refractometer once fermentation has begun. While excellent for testing sugar in the vineyard or the initial must, a refractometer measures the refractive index of a liquid. Once yeast begins producing ethanol, the alcohol distorts the light path, leading to a falsely high reading that suggests the wine has stopped fermenting. Unless you are using a complex correction calculator, the refractometer is unreliable for monitoring active wine fermentation. Ensure you have an accurate reading with a hydrometer before proceeding.
2. Temperature Management
Wine yeast strains have specific temperature windows. If your cellar or fermentation area has dropped below the recommended range for your specific strain, the yeast may have entered a dormant state.
Move the fermenter: Shift the vessel to a warmer area or use a heating belt/pad.
Target Range: For most red wines, a temperature of 21–27°C (70–80°F) is often needed to finish the last few degrees of Brix. For whites, ensure you aren't dropping below 15°C (60°F).
Rouse the lees: Gently stir the bottom of the fermenter with a sanitized paddle to bring the yeast back into contact with the remaining sugars.
3. Nutrient Intervention (via MoreWine.com)
By the time a fermentation reaches its final stages, the initial nutrients in the grape must are often depleted. A "stuck" fermentation is frequently a sign of nitrogen or micronutrient starvation.
We recommend utilizing professional-grade additives found at MoreWine.com to revitalize your colony. Adding Fermaid K or Fermaid O provides the essential nitrogen, vitamins, and minerals that yeast require to survive the increasingly toxic (high alcohol) environment of a finishing wine. If you are early in the process, Go-Ferm can also be used during the rehydration of rescue yeast to ensure they are at peak health.
4. Re-Pitching with a "Restart" Yeast
If the gravity has not moved after 48 hours of temperature and nutrient adjustments, you likely need to "restart" the fermentation with a more robust yeast strain.
Select a yeast with a high alcohol tolerance and a neutral sensory profile to ensure the original character of your fruit remains the star. We highly recommend Uvaferm 43—widely considered the industry standard for restarting stuck fermentations due to its ability to ferment in high-alcohol, high-$SO_2$ environments. Alternatively, Lalvin EC-1118 is a reliable, neutral workhorse that can finish even the most difficult fermentations.