stuck ferm

Dan,

Stuck fermentations can be due to a lack of nitrogen, excessively low or high temperatures, the lack of an essential yeast nutrient, the use of damaged yeast, etc. Whatever the cause, a stuck fermentation should be restarted as quickly as possible.

Use a thermometer to make sure the temperature of the stuck fermentation is neither too high nor too low. Then get some air into the stuck fermentation. Sometimes a little splashing and bubbling will be enough to rejuvenate the yeast and restart a stuck wine. If nitrogen deficiency is expected, diammonium phosphate should be added to the stuck wine. If the fermentation stopped early with lots of sugar remaining, the additional nitrogen may restart fermentation. On the other hand, when little sugar remains, the stuck fermentation should be re-inoculated with a fresh batch of alcohol tolerant yeast (Prise de Mousse or Pasteur Champagne) after the nitrogen addition.

Sometimes, more effort is required to restart a stuck fermentation. The following method is often successful IF the original problem has been corrected. (1) Make a gallon of starter using either Pasteur Champagne or Prise de Mousse yeast. (2) When the starter is active, add a gallon of the stuck wine. (3) Wait until the starter becomes active again, and then add two gallons of stuck wine. (4) Wait until the starter is active again then add four gallons of stuck wine. (5) Continue this doubling process until all of the stuck wine has been added.

Once active fermentation is underway, the wine should be monitored carefully by measuring Brix twice a day. When the hydrometer is steady and reads less than zero, the wine should be tested with a Clinitest tablet to be sure all the sugar is gone.

Good luck, Lum Del Mar, California, USA