hazarding a guess...
Given the potency of Old Rasputin (10 per cent or so, as I recall), it could simply be the alcohol doing a number on the digestive tract. the other strong possibility is that you may have a bit of an allergy to the unmalted barley present in most stouts. while beer is produced using grains (usually barley) which have been malted (that is to say, the starch has been converted to sugar), in most stouts, a proportion of unmalted (albeit heavily-roasted) barley is used, to help darken the colour, and to add some of the bitterness/roast coffee flavours you sometimes get. i also know of some imperial stouts (dogfish head worldwide, if you know it), where substantial amounts of sulphites have been found (and some folks are fairly allergic to sulphites).
the other possibility is if they old rasputin is bottle conditioned, which i believe it is, that means the yeast is still alive/active, which could be causing your tummy to turn somersaults.
happy drinking!
tuqueboy
(tuqueboy has been in a medically -induced coma since, Mon 3 Nov 2008, 17:21, Reply)