Another one to track down ... yesterday MH mentioned on the Imperial Rome list this claim, from the Star:

The term “toasting” was said to have come into being during the Roman era. The Romans customarily dropped a piece of toasted bread in wine to make it more palatable – in those days, wine had only just been discovered and could not have been very good; the carbon in burnt bread would have absorbed some of the harsher elements and would have been discarded after soaking.

The Star originates in Malaysia and, as an aside, it's one of the news sources I look at but generally avoid for Explorator because the editorial standards often seem suspect. Still, it is clear that this particular claim is well-bruited about the web. It's mentioned, e.g., in an article about toast at Interesting Thing of the Day (which is generally well-researched ... generally) and at, among numerous other places.

Whatever the case, this explanation doesn't seem to 'get' the non-sequitur aspect of this supposed origin tale (how do you go from putting burnt bread in a cup of wine to praising the guest of honour and raising the glass?), but can anyone cite a source for this 'custom' of putting burnt bread into wine? I mean we're already cutting the wine with water in ancient times ... when did we start putting stuff in it?