Rav Henkin in a later responsum on the subject retracts his reservations regarding using grape juice for a different reason. He consulted with Mr. Herzog, of Herzog Winery fame, who demonstrated to him how one can easily fermented even pasteurized grape juice by adding a little sugar and yeast and leaving it exposed, thus refuting the pasteurization argument from a scientific perspective as well.
Just wondering, can we compare the ability for juice to ferment naturally, to when it needs human intervention to make it ferment?
I know many people who, although they use grape juice for
kiddush all year, are
makpid to use wine, or home-squeezed grapes for the 4 cups on
Pesach because of this fermenting reason/problem. I also personally know a well renowned and respected
rav/rabbi who is
makpid to use for the 4
kosos only wine not containing sulfites. Though, I'm not quite sure why, and whether it has to do with the fermenting issue.