I last had (several) FES in the Caribbean about 10 years ago. Since they recently starting exporting to the US, I picked up a six pack at BevMo. While I still enjoy it greatly, I recall it having a pleasantly sour finish that is lacking in the current beers.
I remember reading that Guinness used to export some sort of un-fermented, hopped wort to regional breweries in Africa and the Caribbean where they would complete the brewing process. Is it possible that wort had a lactobaccilus infection that gave the stout some sour notes? Is this something I could reproduce using the "sour mash" technique in the current Zymurgy issue?