Sounds like H2S. Has fermentation stopped? Do you detect a rotten egg smell? If, so, you might try to introduce copper into the wine to take up some of the Sulfur. What I have done successfully is to take the copper ground wire out of a three wire cable (Romex) and fashion a whisk with it. You will need about 6 feet of wire. Stir the wine well with the wire whisk and let the wire hang in the wine over night. Should take up the Sulfur. To restart fermentation take about a quart of wine, warm it on the range (do not boil it) to about 100 degrees, add a tsp of yeast and a tbsp of sugar and get it working vigorously, then introduce it into the wine slowly, stirring slowly.