We all know that the subject of corks v screwcaps is a horribly political one. There are now factions, especially in New Zealand where screwcaps are already so prevalent, which either do or do not claim that using screwcaps can lead to reduction and therefore hydrogen sulfide, in wine (look it up in The Oxford Companion to Wine!).
In response to the screwcaps-lead-to-reduction argument, Alistair Maling MW, Group Winemaker at Villa Maria in NZ which has gone entirely over to screwcap for reds as well as whites, chips in with the following explanation for the occurrence of hydrogen sulfide in some screwcapped wines:
Hydrogen sulfide...