Originally Posted by brighamj
I actually have a theory as to what may have happened. If I'm right, it is all operator error.
I brew on a single tier, three kettle set-up. When I'm done with my saccharification rest and I bring the temp up to the high 160's for the mashout, I think I may have adopted the possibly bad habit of turning the burner on under the mash kettle. I am unsure if I did this on all of the bad batches or not -- bad memory. I know I did on at least one.
My thought is that by using the burner in conjunction with the HERMS, in an effort to raise the temperature more quickly, I may be raising the temperature of the bottom of the grain bed to a level where tannins are being extracted.
There is 1.5" between the bottom of the kettle and the false bottom (bottom of the grain bed), with a single exit point for the mash. If there are any "eddies" in this bottom layer, it may explain the heat differential.
The temperature probe is inches above the false bottom, and perhaps there are in fact layers of heat differential.
If it's tannins, that would completely depend on water PH and potentially be due to over-sparging. If it was heat alone could leach tannins, then decoction mashing (where you pull off some grain/liquid and boil it, then return to the mash) would result in heavily tannic, astringent beers instead of the rich malty hoffbrau haus beers. So if tannins are the problem, it was probably that your sparge water wasn't acidic enough to compensate for reduced acidity in the mash post pulling first runnings.
You may have also scorched the wort, but that would give a burnt bitterness which you'd probably be able to taste.
Other than that, the double heating sounds like a reasonable approach.
Originally Posted by anico4704
I would try building some RO water from scratch, sounds like a water issue to me .
^ This from a sparge water perspective.