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It is great to be able to contribute to a discussion of such significance.
Like John Wisemen, I have oft succumbed to the pleasures of drinking
Guinness in Ireland. I know that it is exported all over the world but
unless you have tried it in the country of its origin you will not
appreciate what a drink it is.

Back to the point.  I was reading how after drinking Guinness John didn't
get the reaction he expected from it and wonder if the method of
manufacture of the malt has anything to do with it.  As has been pointed
out, the barley grains are allowed to just germinate so that the starch
is converted into fermentable sugar.  The grains are then roasted before
these sugars are extracted.  The malt barley used in Guinness is roasted
at a temperature considerably higher than normal beers and this leads to
the much darker colour and burnt taste of the drink.  It may be that this
heat causes a much increased breakdown of the proteins than would
otherwise be the case.

Another contributor has pointed out that the proteins would normally be
filtered out of a beer (clear US type beer that is) but even then I would
guess that some of the shorter peptide sequences could persist and cause
problems. I believe but am not sure (See I admit I do not know
everything.) that Guinness, like a number of other specialist brews, is
filtered less enthusiastically than most of its rivals and will still
contain some yeast etc.

I have worked up quite a thirst writing all this - perhaps just a small
one before going to bed.

To John, Michael, Karen, Joe and all  --  Cheers.

Paul Shattock