Surprisingly, much of it appears to be accurate. Tannins can cause irritation, though more notably of the bladder (interstitial cystitis) than the stomach, and brewing finer coffee at lower temperature does indeed result in a lower tannin content. Ingesting coffee beans does in fact cause some indigestion via increased production of stomach acid, as well, and in addition to all of this caffeine works by the following two neural mechanisms:
* it blocks the adenosine receptor type 1, whose primary function is to decrease blood pressure and heart rate in preparation for sleeping
* it blocks the glycine receptor, whose primary purpose is to slow muscle contraction (strychnine also blocks this receptor, albeit far more strongly...)
So the claims about the effects of coffee are, well, surprisingly accurate, though finding most of this information was hard and I wish I had peer-reviewed sources:
Google Scholar seems to be getting slowly less useful; repeated searches for information on brewing methods turned up mostly information about roasting methods.
