I've been having trouble getting my latest vintage of cabernet sauvignon fully fermented.
Secondary fermentation stopped with about 3 percent unfermented sugar a few months ago. I added heat pads around the three 5-gallon carboys to get fermentation started again. That seemed to work well. My hydrometer tests showed very close to 1.00 specific gravity.
I racked the wine, added oak chips and put the carboys in the cool cellar at the end of December and left it alone to hibernate for the winter.
I took a taste of the cabernet last month while messing with some other wines and was surpised at how sweet it tasted. I took new hydrometer readings and found that there was still a bit of residual sugar in all three carboys.
I started a batch of a high-powered yeast — Red Star Premier Curvee — and added some of that with yeast energizer to all three carboys and brought the heat back up to about 75 degrees. That was about two weeks ago. I removed the heat to return it to 50 degree cellar temperatures last week.
I racked the three carboys again Sunday, took hydrometer readings and tastes. The wines are getting close to where they should be, but there's still some slow fermentation going on and a hint of sweetness, especially in one of the carboys.
I haven't decided at this point whether to add yeast again or let them slowly take care of themselves.