Using Ascorbic Acid to reduce Hydrogen Sulfide:

I've personally had to deal with this (once in 15 yearsof wine making, only takes once, then never again).  Prevention is best byselecting a yeast with low nutrient requirements, knowing your YAN spec's on themust, or just assuring a good nutrient regiment thru the first half offermentation.  I mix equal parts of DAP and Fermax, add 1/2 of thenutrients just before pitching the yeast andbalance 3-4 days later.  Also if I note a slight smell of sulfuradd more in small doses, wait 12 hours and repeat if necessary.

Unfortunately I had a slight sulfer smell and let itprogress too far subsequently forming poly-mercaptans (disulfides) which will not react with copper. This required a series of ascorbic acid treatments to break the chaindown to a simpler compound that copper sulfate could then address.

First run a bench trial to see if Cu alone will help orif you need to be more aggressive with ascorbic acid. The trouble with H2S is it can magnify in the bottle so treat itimmediately it won't go away.

The bench test will help determine if the problem can be resolved easily withcopper.

Here's a good site for details on treating this issue:

http://www.bcawa.ca/winemaking/h2s.htm

One other thing I've learned to treat H2S problems-  After the ascorbic acid / copper sulfate treatment, stir old (expired) ordead wine yeast into the finished wine (200 grams / barrel of old yeast).  AnOld wine maker taught me this.  Theyeast rehydrate themselves and suck up the copper and drop out of suspension. Then rack off the lee's.