I have another theory on astringency in wort and beer. With the make up of Red's water, this may be a candidate.
Tannins are the predominant cause of astringency in brewing. They are complex organic molecules that can complex with metal ions and precipitate out of solution. They also complex with proteins.
For the past several years, I was confused as to why my morning cup of tea tasted better at work than at home. At home I have RO water in the kitchen and at work I have typical Midwestern hard water. On the outset, I assumed that RO water would make better tea since it has very little alkalinity. But invariably, the tea made with the hard tap water was smoother and less astringent even though they are otherwise identical (temp, teabag, etc).
The other week I was reminded of the fact that tannins and metal ions will complex and then it hit me that was what was missing in the RO water. So, I did a quick and unscientific experiment to see if adding calcium to my RO water would make better tasting tea. Before adding the teabag, I dropped in a few pearls of calcium chloride to see if I thought there was a taste improvement. In my opinion, there was!
With this unscientific result, I now need to perform a more scientific analysis of this effect and its perceptions. Calcium chloride is the obvious choice since calcium is moderately flavorless. Gypsum is a candidate, but sulfate introduces its own flavor. Chalk doesn't dissolve adequately, so its out. Magnesium is out too since it adds too much flavor at high concentrations. I figure I'll mix up a couple of CaCl solutions and brew up some strong teas. With some triangle testing with a few subjects, I should be able to discern a cause and effect.
So in Red's case, I think that the calcium content of his brewing water may have been too low to remove much of the tannin that is naturally present in wort. I look forward to hearing what Red has to say with regard to his typical mashing and sparging water calcium content.
By the way, Polyclar will precipitate tannins too.