By definition, a stuck fermentation is a fermentation that has stopped before all the available sugar in the wine has been converted to alcohol and CO2. If the bubbles in your airlock slow down before your wine has reached terminal gravity (usually 1.000 or lower), you may have a stuck fermentation. Were you to give up on the wine at this point, it would taste semi-sweet and generally pretty bad. Not to worry, there are ways to fix this. Before we get into how to fix it, let's make sure that you have a stuck fermentation.
How to tell if you have a stuck fermentation
Is the specific gravity of your wine no longer falling, or tremendously sluggish? If you take Hydrometer readings for three consecutive days, and the reading remains the same and is higher than 1.000, it's probably stuck. Make sure you have a good airtight seal at your Airlock. Ensure that the airlock is firmly seated in the Bung, and the bung is securely seated in the mouth of the Carboy. If there was not an airtight seal, you would not see bubbles out of your airlock. Is the temperature of your fermentation area between 65 and 75 °F? If it is too cold, the yeast can't do it's job (or does it very slowly). Fortunately, stuck fermentations are pretty rare. But when they do happen, it's important to make corrections right away and get the fermentation going again for optimum results.
How to fix a stuck fermentation
- Simply move the fermenter to an area that is room temperature, or 68-70 °F. In most cases, too low a temperature is the cause of a stuck fermentation, and bringing the temp up is enough to get it going again.
- Open up the fermenter, and rouse the yeast by stirring it with a sanitized spoon. Sometimes putting the yeast back in suspension will get it going again.
- Add some Yeast Energizer to the wine. Add 1/2 teaspoon per gallon of wine, and stir well. NOTE: While it may seem like a good idea, Midwest does NOT recommend adding Yeast Nutrient at this point. This may result in leftover vitamins that can stimulate spoilage microbes.
- Rack the wine off of the old yeast, and pitch some fresh yeast in, preferably a highly active strain such as Lavlin EC-1118 or Red Star Premier Cuvee.
If none of these tips get the fermentation going again, as a last resort, you can pitch a yeast starter. Do this by pulling a half gallon of must out of your fermenter. Add 1.5 to 2 teaspoons yeast energizer and a packet of yeast (Lavlin EC-1118 or Red Star Premier Cuvee). Stir this mixture up well, and place in a warm area. Once you see a vigorous fermentation, add it back to the original must.
See our Bottle Knowledge section for more information on How to Make Wine at Home