Restart Stuck Fermentations

All home winemakers wish — and strive — for fermentations that go smoothly and completely to the desired finish, usually dry wine. When things go wrong, a frequent problem is a stuck or sluggish fermentation. In his classic Knowing and Making Wine, Emile Peynaud refers to these conditions as “fermentation stoppage” and calls that a sign of “stoppage in the growth and the death of yeasts.” There you have it. If there is still fermentable sugar left, but your yeast stops growing or dies, you have a stuck fermentation. The signs of stuck fermentation depend upon the kind of wine being made. For red wine from fresh or frozen grapes fermenting on the skins, normal fermentation produces a “cap” of floating inflated skins that needs to be punched down or pumped over two or three times a day. At the end of a good fermentation, the cap will come up more slowly, it will be softer, and you can see puddles of wine among the skins when punch-down time comes around. When those conditions prevail, a hydrometer check should show