The most common source of sulfur smell (hydrogen sulfide = H2S) in aging wine is a byproduct of unhappy yeast. Best way that I know to get rid of it is to stir the wine 'vigorously' to aerate it and drive off the sulfur smell. Also, judicious addition of copper sulfate stirred into the wine will remove the smell. Please search the wine FAQ and Lum Eisman's and Jack Keller's and Ben Rotter's excellent sites 'wine defects' areas for instruction on how much coppper sulfate to use. You want to use the miminum effective amount (absolute maximum about 250ppm, typically 50-100ppm).
You haven't mentioned how many times you've racked your wine off the sediment. The more yeast remaining in the wine, the more the potential for hydrogen sulfide generation. I, for one, do sur lie (on the lees) aging of many of my wines, and I have to stir the lees gently about every two weeks to prevent 'unhappy yeast' hydrogen sulfide generation. Please note that maintaining proper free sulfite (SO2) concentration is needed to protect the wine from oxidation, not hydrogen sulfide. Typical recommended levels of free SO2 are 20-50ppm.
The air that gets stirred into your wine is temporary (i.e. gets reacted with the free SO2) and is 'neutralized' by the free SO2 in a day or so. It is constant exposure to air via too much headspace or an incomplete seal of the container that leads to oxidation of the wine.
We learn from our mistakes. Happy winemaking, Gene
Werner
