I just cracked open the first bottles of the first brew I have brewed with *modified* water, and was a bit surprised with the results... Against the most likely very sensible advice of Altbier bitte (http://www.brewersfriend.com/forum/viewtopic.php?f=3&t=82), I added CaCl to the tap water available here, in an attempt to reduce the overall bitterness of the beer I have been brewing. The good news is, it seems to have worked. This batch is overall less bitter than the last ~4-5 batches, even though the recipe is much the same but the IBUs are higher. And, even better, the beer is mighty tasty! (this brew is >7%, which balances out the higher malty flavor resulting from the higher Cl content) The one thing that is bugging me though, is the slight butterscotch flavor/aroma that has become noticeable. I don't really have any experience with diacetyl, so I am not sure if that is what I am dealing with. But the flavor/aroma of butterscotch is fairly distinctive in this brew, even though it is pretty much the same recipe as that past 4 brews, with only a change in the water chemistry (and hop variety). normally my water looks like this: Ca Mg SO Na Cl HCO 76 15 166 27 44 55 w/+ 7g CaCl, it looks like this: Ca Mg SO Na Cl HCO 131 15 166 27 140 55 Could this be the reason for the (potential) diacetyl flavors, or am I barking up the wrong tree?